| 1 | .ds [[ \fR\z[\h'.15m'[\fP |
| 2 | .ds ]] \fR\z]\h'.15m']\fP |
| 3 | .ND "4 June 1979" |
| 4 | . .TM 79-1273-6 39199 39199-11 |
| 5 | .RP |
| 6 | .TL |
| 7 | The Programming Language EFL |
| 8 | .AU "MH 2C-570" 2059 |
| 9 | Stuart I. Feldman |
| 10 | .AI |
| 11 | .MH |
| 12 | .OK |
| 13 | Fortran |
| 14 | Preprocessors |
| 15 | Ratfor |
| 16 | .AB |
| 17 | .PP |
| 18 | EFL is a clean, general purpose computer language intended to encourage |
| 19 | portable programming. |
| 20 | It has a uniform and readable syntax and good data and control flow structuring. |
| 21 | EFL programs can be translated into efficient Fortran code, |
| 22 | so the EFL programmer can take advantage of the ubiquity of Fortran, |
| 23 | the valuable libraries of software written in that language, and the portability |
| 24 | that comes with the use of a standardized language, |
| 25 | without suffering from Fortran's many failings as a language. |
| 26 | It is especially useful for numeric programs. |
| 27 | The EFL language permits the programmer to express |
| 28 | complicated ideas in a comprehensible way, |
| 29 | while permitting access to the power of the Fortran environment. |
| 30 | EFL can be viewed as a descendant of B. W. Kernighan's Ratfor [1]; |
| 31 | the name originally stood for `Extended Fortran Language'. |
| 32 | The current version of the EFL compiler is written in |
| 33 | portable C. |
| 34 | .AE |
| 35 | .CS 35 0 35 0 0 1 |
| 36 | .SH |
| 37 | .ds ~ \\v'.25m'\\s+2~\\s-2\\v'-.25m' |
| 38 | .if n .ls 2 |
| 39 | .EQ |
| 40 | delim @@ |
| 41 | .EN |
| 42 | .NH 1 |
| 43 | INTRODUCTION |
| 44 | .NH 2 |
| 45 | Purpose |
| 46 | .PP |
| 47 | EFL is a clean, general purpose computer language intended to encourage |
| 48 | portable programming. |
| 49 | It has a uniform and readable syntax and good data and control flow structuring. |
| 50 | EFL programs can be translated into efficient Fortran code, |
| 51 | so the EFL programmer can take advantage of the ubiquity of Fortran, |
| 52 | the valuable libraries of software written in that language, and the portability |
| 53 | that comes with the use of a standardized language, |
| 54 | without suffering from Fortran's many failings as a language. |
| 55 | It is especially useful for numeric programs. |
| 56 | Thus, the EFL language permits the programmer to express |
| 57 | complicated ideas in a comprehensible way, |
| 58 | while permitting access to the power of the Fortran environment. |
| 59 | .NH 2 |
| 60 | History |
| 61 | .PP |
| 62 | EFL can be viewed as a descendant of B. W. Kernighan's Ratfor [1]; |
| 63 | the name originally stood for `Extended Fortran Language'. |
| 64 | A. D. Hall designed the initial version of the language and wrote a preliminary version of a compiler. |
| 65 | I extended and modified the language and wrote a full compiler (in C) for it. |
| 66 | The current compiler is much more than a simple preprocessor: |
| 67 | it attempts to diagnose all syntax errors, to provide readable Fortran output, |
| 68 | and to avoid a number of niggling restrictions. To achieve this goal, a sizable two-pass translator is needed. |
| 69 | .NH 2 |
| 70 | Notation |
| 71 | .PP |
| 72 | In examples and syntax specifications, |
| 73 | .B boldface |
| 74 | type is used to indicate literal words and punctuation, such as |
| 75 | \fBwhile\fR. |
| 76 | Words in |
| 77 | .I italic |
| 78 | type |
| 79 | indicate an item in a category, such as an |
| 80 | .I expression. |
| 81 | A construct surrounded by double brackets represents a list of one or more of those items, separated by commas. |
| 82 | Thus, the notation |
| 83 | .DS C |
| 84 | \fI\*([[ item \*(]]\fR |
| 85 | .DE |
| 86 | could refer to any of the following: |
| 87 | .DS B |
| 88 | .I |
| 89 | item |
| 90 | item\fB, \fIitem |
| 91 | \fIitem\fB, \fIitem\fB, \fIitem\fR |
| 92 | .DE |
| 93 | .PP |
| 94 | The reader should have a fair degree of familiarity with some procedural language. |
| 95 | There will be occasional references to Ratfor and to Fortran |
| 96 | which may be ignored if the reader is unfamiliar with those languages. |
| 97 | .bp |
| 98 | .NH 1 |
| 99 | LEXICAL FORM |
| 100 | .NH 2 |
| 101 | Character Set |
| 102 | .PP |
| 103 | The following characters are legal in an EFL program: |
| 104 | .KS |
| 105 | .TS |
| 106 | center; |
| 107 | ll. |
| 108 | \fIletters \fBa b c d e f g h i j k l m\fI |
| 109 | \fBn o p q r s t u v w x y z\fI |
| 110 | digits \fB0 1 2 3 4 5 6 7 8 9\fI |
| 111 | white space \fIblank tab\fI |
| 112 | quotes \fB\' "\fI |
| 113 | sharp \fB#\fI |
| 114 | continuation \fB\(ru\fI |
| 115 | braces \fB{ }\fI |
| 116 | parentheses \fB( )\fI |
| 117 | other \fB, ; : . + \- \(** /\fI |
| 118 | \fB= < > & \*~ | $\fI |
| 119 | .TE |
| 120 | .KE |
| 121 | Letter case (upper or lower) is ignored except within strings, |
| 122 | so `\fBa\fR' and `\fBA\fR' are treated as the same character. |
| 123 | All of the examples below are printed in lower case. |
| 124 | An exclamation mark (`\fB!\fR') may be used in place of a tilde (`\fB\*~\fR'). |
| 125 | Square brackets (`[' and `]') may be used in place of braces (`{' and `}'). |
| 126 | .NH 2 |
| 127 | Lines |
| 128 | .PP |
| 129 | EFL is a line-oriented language. |
| 130 | Except in special cases (discussed below), |
| 131 | the end of a line marks the end of a token and the end of a statement. |
| 132 | The trailing portion of a line may be used for a comment. |
| 133 | There is a mechanism for diverting input from one source file to another, |
| 134 | so a single line in the program may be replaced by a number of lines from the other file. |
| 135 | Diagnostic messages are labeled with the line number of the file on which they are detected. |
| 136 | .NH 3 |
| 137 | White Space |
| 138 | .PP |
| 139 | Outside of a character string or comment, |
| 140 | any sequence of one or more spaces or tab characters acts as a single space. |
| 141 | Such a space terminates a token. |
| 142 | .NH 3 |
| 143 | Comments |
| 144 | .PP |
| 145 | A comment may appear at the end of any line. |
| 146 | It is introduced by a sharp (#) character, |
| 147 | and continues to the end of the line. |
| 148 | (A sharp inside of a quoted string does not mark a comment.) |
| 149 | The sharp and succeeding characters on the line are discarded. |
| 150 | A blank line is also a comment. |
| 151 | Comments have no effect on execution. |
| 152 | .NH 3 |
| 153 | Include Files |
| 154 | .PP |
| 155 | It is possible to insert the contents of a file at a point in the source text, |
| 156 | by referencing it in a line like |
| 157 | .DS C |
| 158 | .B |
| 159 | include joe |
| 160 | .R |
| 161 | .DE |
| 162 | No statement or comment may follow an |
| 163 | .B include |
| 164 | on a line. |
| 165 | In effect, the |
| 166 | .B include |
| 167 | line is replaced by the lines in the named file, |
| 168 | but diagnostics refer to the line number in the included file. |
| 169 | \fBInclude\fRs may be nested at least ten deep. |
| 170 | .NH 3 |
| 171 | Continuation |
| 172 | .PP |
| 173 | Lines may be continued explicitly by using the underscore (\fB_\fR) character. |
| 174 | If the last character of a line (after comments and trailing white space have been stripped) is an underscore, |
| 175 | the end of line and the initial blanks on the next line are ignored. |
| 176 | Underscores are ignored in other contexts (except inside of quoted strings). |
| 177 | Thus |
| 178 | .DS B |
| 179 | 1_000_000_ |
| 180 | 000 |
| 181 | .DE |
| 182 | equals @10 sup 9@. |
| 183 | .PP |
| 184 | There are also rules for continuing lines automatically: |
| 185 | the end of line is ignored whenever it is obvious that the statement is not complete. |
| 186 | To be specific, a statement is continued if the last token on a line is an operator, comma, |
| 187 | left brace, or left parenthesis. |
| 188 | (A statement is not continued just because of unbalanced braces or parentheses.) |
| 189 | Some compound statements are also continued automatically; |
| 190 | these points are noted in the sections on executable statements. |
| 191 | .NH 3 |
| 192 | Multiple Statements on a Line |
| 193 | .PP |
| 194 | A semicolon terminates the current statement. |
| 195 | Thus, it is possible to write more than one statement on a line. |
| 196 | A line consisting only of a semicolon, or a semicolon following a semicolon, forms a null statement. |
| 197 | .NH 2 |
| 198 | Tokens |
| 199 | .PP |
| 200 | A program is made up of a sequence of tokens. |
| 201 | Each token is a sequence of characters. |
| 202 | A blank terminates any token other than a quoted string. |
| 203 | End of line also terminates a token unless explicit continuation (see above) is signaled by an underscore. |
| 204 | .NH 3 |
| 205 | Identifiers |
| 206 | .PP |
| 207 | An identifier is a letter or a letter followed by letters or digits. |
| 208 | The following is a list of the reserved words that have special meaning in EFL. |
| 209 | They will be discussed later. |
| 210 | .KF |
| 211 | .TS |
| 212 | center; |
| 213 | lll . |
| 214 | .B |
| 215 | array exit precision |
| 216 | automatic external procedure |
| 217 | break false read |
| 218 | call field readbin |
| 219 | case for real |
| 220 | character function repeat |
| 221 | common go return |
| 222 | complex goto select |
| 223 | continue if short |
| 224 | debug implicit sizeof |
| 225 | default include static |
| 226 | define initial struct |
| 227 | dimension integer subroutine |
| 228 | do internal true |
| 229 | double lengthof until |
| 230 | doubleprecision logical value |
| 231 | else long while |
| 232 | end next write |
| 233 | equivalence option writebin |
| 234 | .R |
| 235 | .TE |
| 236 | .KE |
| 237 | The use of these words is discussed below. |
| 238 | These words may not be used for any other purpose. |
| 239 | .NH 3 |
| 240 | Strings |
| 241 | .PP |
| 242 | A character string is a sequence of characters surrounded by quotation marks. |
| 243 | If the string is bounded by single-quote marks ( \fB\'\fR ), it may contain double |
| 244 | quote marks ( \fB"\fR ), and vice versa. |
| 245 | A quoted string may not be broken across a line boundary. |
| 246 | .DS |
| 247 | .B |
| 248 | \'hello there\' |
| 249 | "ain\'t misbehavin\'" |
| 250 | .R |
| 251 | .DE |
| 252 | .NH 3 |
| 253 | Integer Constants |
| 254 | .PP |
| 255 | An integer constant is a sequence of one or more digits. |
| 256 | .DS B |
| 257 | .B |
| 258 | 0 |
| 259 | 57 |
| 260 | 123456 |
| 261 | .R |
| 262 | .DE |
| 263 | .NH 3 |
| 264 | Floating Point Constants |
| 265 | .PP |
| 266 | A floating point constant contains a dot and/or an exponent field. |
| 267 | An |
| 268 | .I "exponent field" |
| 269 | is a letter |
| 270 | .B d |
| 271 | or |
| 272 | .B e |
| 273 | followed by an optionally signed integer constant. |
| 274 | If |
| 275 | @I@ |
| 276 | and |
| 277 | @J@ |
| 278 | are integer constants and |
| 279 | @E@ |
| 280 | is an exponent field, then a floating constant has one of the following forms: |
| 281 | .DS B |
| 282 | .I |
| 283 | \fB.\fPI |
| 284 | I\fB.\fP |
| 285 | I\fB.\fPJ |
| 286 | IE |
| 287 | I\fB.\fPE |
| 288 | \fB.\fPIE |
| 289 | I\fB.\fPJE |
| 290 | .R |
| 291 | .DE |
| 292 | .NH 3 |
| 293 | Punctuation |
| 294 | .PP |
| 295 | Certain characters are used to group or separate objects in the language. |
| 296 | These are |
| 297 | .TS |
| 298 | center; |
| 299 | ll. |
| 300 | parentheses ( ) |
| 301 | braces { } |
| 302 | comma , |
| 303 | semicolon ; |
| 304 | colon : |
| 305 | end-of-line |
| 306 | .TE |
| 307 | The end-of-line is a token (statement separator) |
| 308 | when the line is neither blank nor continued. |
| 309 | .NH 3 |
| 310 | Operators |
| 311 | .PP |
| 312 | The EFL operators are written as sequences of one or more |
| 313 | non-alphanumeric characters. |
| 314 | .DS B |
| 315 | + \- \(** / \(**\(** |
| 316 | < <= > >= == \*~= |
| 317 | && |\|| & | |
| 318 | += \-= \(*= /= \(**\(**= |
| 319 | &&= |\||= &= |= |
| 320 | \-> . $ |
| 321 | .DE |
| 322 | A dot (`\fB.\fR') is an operator when it qualifies a structure element name, |
| 323 | but not when it acts as a decimal point in a numeric constant. |
| 324 | There is a special mode (see the Atavisms section) |
| 325 | in which some of the operators may be represented by a string consisting of a dot, an identifier, and a dot |
| 326 | (\fIe.g., \fB.lt.\fR ). |
| 327 | .NH 2 |
| 328 | Macros |
| 329 | .PP |
| 330 | EFL has a simple macro substitution facility. |
| 331 | An identifier may be defined to be equal to a string of tokens; |
| 332 | whenever that name appears as a token in the program, |
| 333 | the string replaces it. |
| 334 | A macro name is given a value in a |
| 335 | .B define |
| 336 | statement like |
| 337 | .DS |
| 338 | define count n += 1 |
| 339 | .DE |
| 340 | Any time the name |
| 341 | .B count |
| 342 | appears in the program, it is replaced by the statement |
| 343 | .DS C |
| 344 | .B |
| 345 | n += 1 |
| 346 | .R |
| 347 | .DE |
| 348 | A |
| 349 | .B define |
| 350 | statement must appear alone on a line; |
| 351 | the form is |
| 352 | .DS C |
| 353 | \fBdefine \fIname \fIrest-of-line\fR |
| 354 | .DE |
| 355 | Trailing comments are part of the string. |
| 356 | .NH 1 |
| 357 | PROGRAM FORM |
| 358 | .NH 2 |
| 359 | Files |
| 360 | .PP |
| 361 | A |
| 362 | .I file |
| 363 | is a sequence of lines. |
| 364 | A file is compiled as a single unit. |
| 365 | It may contain one or more procedures. |
| 366 | Declarations and options that appear outside of a procedure |
| 367 | affect the succeeding procedures on that file. |
| 368 | .NH 2 |
| 369 | Procedures |
| 370 | .PP |
| 371 | Procedures are the largest grouping of statements in EFL. |
| 372 | Each procedure has a name by which it is invoked. |
| 373 | (The first procedure invoked during execution, known as the |
| 374 | .I main |
| 375 | procedure, |
| 376 | has the null name.) |
| 377 | Procedure calls and argument passing are discussed in Section 8. |
| 378 | .NH 2 |
| 379 | Blocks |
| 380 | .PP |
| 381 | Statements may be formed into groups inside of a procedure. |
| 382 | To describe the scope of names, it is convenient to introduce the ideas of |
| 383 | .I block |
| 384 | and of |
| 385 | .I "nesting level." |
| 386 | The beginning of a program file is at nesting level zero. |
| 387 | Any options, macro definitions, |
| 388 | or variable declarations there are also at level zero. |
| 389 | The text immediately following a |
| 390 | .B procedure |
| 391 | statement is at level 1. |
| 392 | After the declarations, |
| 393 | a left brace marks the beginning of a new block and increases the nesting level by 1; |
| 394 | a right brace drops the level by 1. |
| 395 | (Braces inside declarations do not mark blocks.) |
| 396 | (See Section 7.2). |
| 397 | An |
| 398 | .B end |
| 399 | statement marks the end of the procedure, level 1, and the return to level 0. |
| 400 | A name |
| 401 | (variable or macro) |
| 402 | that is defined at level |
| 403 | @k@ |
| 404 | is defined throughout that block and in all deeper nested levels in which that name is not |
| 405 | redefined or redeclared. |
| 406 | Thus, a procedure might look like the following: |
| 407 | .DS B |
| 408 | .ta .7i 1.4i 2.1i 2.8i |
| 409 | .B |
| 410 | # block 0 |
| 411 | procedure george |
| 412 | real x |
| 413 | x = 2 |
| 414 | . . . |
| 415 | if(x > 2) |
| 416 | { # new block |
| 417 | integer x # a different variable |
| 418 | do x = 1,7 |
| 419 | write(,x) |
| 420 | . . . |
| 421 | } # end of block |
| 422 | end # end of procedure, return to block 0 |
| 423 | .DE |
| 424 | .NH 2 |
| 425 | Statements |
| 426 | .PP |
| 427 | A statement is terminated by end of line or by a semicolon. |
| 428 | Statements are of the following types: |
| 429 | .DS B |
| 430 | Option |
| 431 | Include |
| 432 | Define |
| 433 | .sp .3 |
| 434 | Procedure |
| 435 | End |
| 436 | .sp .3 |
| 437 | Declarative |
| 438 | Executable |
| 439 | .DE |
| 440 | The |
| 441 | .B option |
| 442 | statement is described in Section 10. |
| 443 | The |
| 444 | .B include, |
| 445 | .B define, |
| 446 | and |
| 447 | .B end |
| 448 | statements have been described above; |
| 449 | they may not be followed by another statement on a line. |
| 450 | Each procedure begins with a |
| 451 | .B procedure |
| 452 | statements and finishes with an |
| 453 | .B end |
| 454 | statement; these are discussed in Section 8. |
| 455 | Declarations describe types and values of variables and |
| 456 | procedures. |
| 457 | Executable statements cause specific actions to be taken. |
| 458 | A block is an example of an executable statement; it is made up |
| 459 | of declarative and executable statements. |
| 460 | .NH 2 |
| 461 | Labels |
| 462 | .PP |
| 463 | An executable statement may have a |
| 464 | .I label |
| 465 | which may be used in a branch statement. |
| 466 | A label is an identifier followed by a colon, as in |
| 467 | .DS B |
| 468 | .B |
| 469 | .ta 1i |
| 470 | read(, x) |
| 471 | if(x < 3) goto error |
| 472 | . . . |
| 473 | error: fatal("bad input") |
| 474 | .R |
| 475 | .DE |
| 476 | .NH 1 |
| 477 | DATA TYPES AND VARIABLES |
| 478 | .PP |
| 479 | EFL supports a small number of basic (scalar) types. |
| 480 | The programmer may define objects made up of variables of basic type; |
| 481 | other aggregates may then be defined in terms of previously defined aggregates. |
| 482 | .NH 2 |
| 483 | Basic Types |
| 484 | .PP |
| 485 | The basic types are |
| 486 | .DS B |
| 487 | \fBlogical |
| 488 | \fBinteger |
| 489 | \fBfield(\fIm\|\fB:\fIn\|\fB) |
| 490 | \fBreal |
| 491 | \fBcomplex |
| 492 | \fBlong real |
| 493 | \fBlong complex |
| 494 | \fBcharacter(\fIn\|\fB) |
| 495 | .R |
| 496 | .DE |
| 497 | A logical quantity may take on the two values true and false. |
| 498 | An integer may take on any whole number value in some machine-dependent range. |
| 499 | A field quantity is an integer restricted to a particular closed interval |
| 500 | @([m:n])@. |
| 501 | A `real' quantity is a floating point approximation to a real or rational number. |
| 502 | A long real is a more precise approximation to a rational. |
| 503 | (Real quantities are represented as single precision floating point numbers; |
| 504 | long reals are double precision floating point numbers.) |
| 505 | A complex quantity is an approximation to a complex number, and is represented as a pair of reals. |
| 506 | A character quantity is a fixed-length string of @n@ characters. |
| 507 | .NH 2 |
| 508 | Constants |
| 509 | .PP |
| 510 | There is a notation for a constant of each basic type. |
| 511 | .LP |
| 512 | A logical may take on the two values |
| 513 | .DS B |
| 514 | .B |
| 515 | true |
| 516 | false |
| 517 | .R |
| 518 | .DE |
| 519 | An integer or field constant is a fixed point constant, |
| 520 | optionally preceded by a plus or minus sign, as in |
| 521 | .DS B |
| 522 | .B |
| 523 | 17 |
| 524 | \-94 |
| 525 | +6 |
| 526 | 0 |
| 527 | .R |
| 528 | .DE |
| 529 | A long real (`double precision') constant is a floating point constant containing an exponent field that |
| 530 | begins with the letter |
| 531 | .B d. |
| 532 | A real (`single precision') constant is any other floating point constant. |
| 533 | A real or long real constant may be preceded by a plus or minus sign. |
| 534 | The following are valid |
| 535 | .B real |
| 536 | constants: |
| 537 | .DS B |
| 538 | .B |
| 539 | 17.3 |
| 540 | \-.4 |
| 541 | 7.9e\-6 @(~=~7.9 times 10 sup -6 )@ |
| 542 | 14e9 @(~=~1.4 times 10 sup 10 )@ |
| 543 | .R |
| 544 | .DE |
| 545 | The following are valid |
| 546 | .B "long real" |
| 547 | constants |
| 548 | .DS B |
| 549 | .B |
| 550 | 7.9d\-6 @(~=~7.9 times 10 sup -6 )@ |
| 551 | 5d3 |
| 552 | .R |
| 553 | .DE |
| 554 | .LP |
| 555 | A character constant is a quoted string. |
| 556 | .NH 2 |
| 557 | Variables |
| 558 | .PP |
| 559 | A variable is a quantity with a name and a location. |
| 560 | At any particular time the variable may also have a value. |
| 561 | (A variable is said to be |
| 562 | .I undefined |
| 563 | before it is initialized or assigned its first value, |
| 564 | and after certain indefinite operations are performed.) |
| 565 | Each variable has certain attributes: |
| 566 | .NH 3 |
| 567 | Storage Class |
| 568 | .PP |
| 569 | The association of a name and a location is either |
| 570 | transitory or permanent. |
| 571 | Transitory association is achieved when arguments are passed to procedures. |
| 572 | Other associations are permanent (static). |
| 573 | (A future extension of EFL may include dynamically allocated variables.) |
| 574 | .NH 3 |
| 575 | Scope of Names |
| 576 | .PP |
| 577 | The names of |
| 578 | common areas |
| 579 | are global, |
| 580 | as are procedure names: |
| 581 | these names may be used anywhere in the program. |
| 582 | All other names are local to the block in which they are declared. |
| 583 | .NH 3 |
| 584 | Precision |
| 585 | .PP |
| 586 | Floating point variables are either of normal or |
| 587 | .B long |
| 588 | precision. |
| 589 | This attribute may be stated independently of the basic type. |
| 590 | .NH 2 |
| 591 | Arrays |
| 592 | .PP |
| 593 | It is possible to declare rectangular arrays (of any dimension) of values of the same type. |
| 594 | The index set is always a cross-product of intervals of integers. |
| 595 | The lower and upper bounds of the intervals must be constants for arrays that are local or |
| 596 | .B common. |
| 597 | A formal argument array may have intervals that are of length equal to one of the other formal arguments. |
| 598 | An element of an array is denoted by the array name followed by a parenthesized comma-separated list of integer values, |
| 599 | each of which must lie within the corresponding interval. |
| 600 | (The intervals may include negative numbers.) |
| 601 | Entire arrays may be passed as procedure arguments or in input/output lists, |
| 602 | or they may be initialized; |
| 603 | all other array references must be to individual elements. |
| 604 | .NH 2 |
| 605 | Structures |
| 606 | .PP |
| 607 | It is possible to define new types which are made up of elements of other types. |
| 608 | The compound object is known as a |
| 609 | .I structure; |
| 610 | its constituents are called |
| 611 | .I members |
| 612 | of the structure. |
| 613 | The structure may be given a name, |
| 614 | which acts as a type name in the remaining statements within the scope of its declaration. |
| 615 | The elements of a structure may be of any type |
| 616 | (including previously defined structures), |
| 617 | or they may be arrays of such objects. |
| 618 | Entire structures may be passed to procedures or be used in input/output lists; |
| 619 | individual elements of structures may be referenced. |
| 620 | The uses of structures will be detailed below. |
| 621 | The following structure might represent a symbol table: |
| 622 | .DS B |
| 623 | .B |
| 624 | .ta .7i 1.4i 2.1i |
| 625 | struct tableentry |
| 626 | { |
| 627 | character(8) name |
| 628 | integer hashvalue |
| 629 | integer numberofelements |
| 630 | field(0:1) initialized, used, set |
| 631 | field(0:10) type |
| 632 | } |
| 633 | .DE |
| 634 | .NH 1 |
| 635 | EXPRESSIONS |
| 636 | .PP |
| 637 | Expressions are syntactic forms that yield a value. |
| 638 | An expression may have any of the following forms, recursively applied: |
| 639 | .DS B |
| 640 | .I |
| 641 | primary |
| 642 | \fB(\fI expression \fB)\fI |
| 643 | unary-operator expression |
| 644 | expression binary-operator expression |
| 645 | .DE |
| 646 | In the following table of operators, |
| 647 | all operators on a line have equal precedence |
| 648 | and have higher precedence than operators on later lines. |
| 649 | The meanings of these operators are described in sections 5.3 and 5.4. |
| 650 | .DS B |
| 651 | .B |
| 652 | \-> . |
| 653 | \(**\(** |
| 654 | \(** / \fIunary\fB + \- ++ \-\- |
| 655 | + \- |
| 656 | < <= > >= == \*~= |
| 657 | & && |
| 658 | | |\|| |
| 659 | $ |
| 660 | = += \-= \(**= /= \(**\(**= &= |= &&= |\||= |
| 661 | .R |
| 662 | .DE |
| 663 | Examples of expressions are |
| 664 | .DS B |
| 665 | .B |
| 666 | a<b && b<c |
| 667 | \-(a + sin(x)) / (5+cos(x))\(**\(**2 |
| 668 | .R |
| 669 | .DE |
| 670 | .NH 2 |
| 671 | Primaries |
| 672 | .PP |
| 673 | Primaries are the basic elements of expressions, as follows: |
| 674 | .NH 3 |
| 675 | Constants |
| 676 | .PP |
| 677 | Constants are described in Section 4.2. |
| 678 | .NH 3 |
| 679 | Variables |
| 680 | .PP |
| 681 | Scalar variable names are primaries. |
| 682 | They may appear on the left or the right side of an assignment. |
| 683 | Unqualified names of aggregates (structures or arrays) |
| 684 | may only appear as procedure arguments and in input/output lists. |
| 685 | .NH 3 |
| 686 | Array Elements |
| 687 | .PP |
| 688 | An element of an array is denoted by the array name followed by a parenthesized list of subscripts, |
| 689 | one integer value for each declared dimension: |
| 690 | .DS B |
| 691 | .B |
| 692 | a(5) |
| 693 | b(6,\|\-3,\|4) |
| 694 | .R |
| 695 | .DE |
| 696 | .NH 3 |
| 697 | Structure Members |
| 698 | .PP |
| 699 | A structure name followed by a dot followed by the name of a member of that structure constitutes a reference to |
| 700 | that element. |
| 701 | If that element is itself a structure, the reference may be further qualified. |
| 702 | .DS B |
| 703 | .B |
| 704 | a.b |
| 705 | x(3).y(4).z(5) |
| 706 | .R |
| 707 | .DE |
| 708 | .NH 3 |
| 709 | Procedure Invocations |
| 710 | .PP |
| 711 | A procedure is invoked by an expression of one of the forms |
| 712 | .DS B |
| 713 | \fIprocedurename \fB( )\fR |
| 714 | \fIprocedurename \fB( \fIexpression\fB )\fR |
| 715 | \fIprocedurename \fB( \fIexpression-1\fB, \fI...\fB, \fIexpression-n \fB)\fR |
| 716 | .DE |
| 717 | The |
| 718 | .I procedurename |
| 719 | is either the name of a variable |
| 720 | declared |
| 721 | .B external |
| 722 | or it is the name of a |
| 723 | function known to the EFL compiler (see Section 8.5), |
| 724 | or it is the actual name of a procedure, as it appears in a |
| 725 | .B procedure |
| 726 | statement. |
| 727 | If a |
| 728 | .I procedurename |
| 729 | is declared |
| 730 | .B external |
| 731 | and is an argument of the current procedure, |
| 732 | it is associated with the procedure name passed as actual argument; |
| 733 | otherwise it is the actual name of a procedure. |
| 734 | Each |
| 735 | .I expression |
| 736 | in the above is called an |
| 737 | .I "actual argument". |
| 738 | Examples of procedure invocations are |
| 739 | .DS B |
| 740 | .B |
| 741 | f(x) |
| 742 | work() |
| 743 | g(x, y+3, 'xx') |
| 744 | .R |
| 745 | .DE |
| 746 | When one of these procedure invocations is to be performed, |
| 747 | each of the actual argument expressions is first evaluated. |
| 748 | The types, precisions, and bounds of actual and formal arguments should agree. |
| 749 | If an actual argument is a variable name, array element, or structure member, |
| 750 | the called procedure is permitted to use the corresponding formal argument as the left side |
| 751 | of an assignment or in an input list; |
| 752 | otherwise it may only use the value. |
| 753 | After the formal and actual arguments are associated, |
| 754 | control is passed to the first executable statement of the procedure. |
| 755 | When a |
| 756 | .B return |
| 757 | statement is executed in that procedure, |
| 758 | or when control reaches the |
| 759 | .B end |
| 760 | statement of that procedure, |
| 761 | the function value is made available as the value of the procedure invocation. |
| 762 | The type of the value is determined by the attributes of |
| 763 | the |
| 764 | .I procedurename |
| 765 | that are declared or implied in the calling procedure, |
| 766 | which must agree with the attributes declared for the function in its procedure. |
| 767 | In the special case of a generic function, |
| 768 | the type of the result is also affected by the type of the argument. |
| 769 | See Chapter 8 for details. |
| 770 | .NH 3 |
| 771 | Input/Output Expressions |
| 772 | .PP |
| 773 | The EFL input/output syntactic forms |
| 774 | may be used as integer primaries that have |
| 775 | a non-zero value |
| 776 | if an error occurs during the input or output. |
| 777 | See Section 7.7. |
| 778 | .NH 3 |
| 779 | Coercions |
| 780 | .PP |
| 781 | An expression of one precision or type may be converted to another by an expression of the form |
| 782 | .DS C |
| 783 | \fIattributes \fB( \fIexpression \fB)\fR |
| 784 | .DE |
| 785 | At present, the only |
| 786 | .I attributes |
| 787 | permitted are precision and basic types. |
| 788 | Attributes are separated by white space. |
| 789 | An arithmetic value of one type may be coerced to any other arithmetic type; |
| 790 | a character expression of one length may be coerced to a character expression of another length; |
| 791 | logical expressions may not be coerced to a nonlogical type. |
| 792 | As a special case, |
| 793 | a quantity of |
| 794 | .B complex |
| 795 | or |
| 796 | .B "long complex" |
| 797 | type may be constructed from two integer or real quantities |
| 798 | by passing two expressions (separated by a comma) in the coercion. |
| 799 | Examples and equivalent values are |
| 800 | .DS B |
| 801 | .B |
| 802 | integer(5.3) = 5 |
| 803 | long real(5) = 5.0d0 |
| 804 | complex(5,3) = @5+3i@ |
| 805 | .R |
| 806 | .DE |
| 807 | Most conversions are done implicitly, |
| 808 | since most binary operators permit operands of different arithmetic types. |
| 809 | Explicit coercions are of most use when it is necessary to convert the type of an actual argument |
| 810 | to match that of the corresponding formal parameter in a procedure call. |
| 811 | .NH 3 |
| 812 | Sizes |
| 813 | .PP |
| 814 | There is a notation which yields the amount of memory required to store a datum |
| 815 | or an item of specified type: |
| 816 | .DS B |
| 817 | \fBsizeof ( \fIleftside\fB ) |
| 818 | \fBsizeof ( \fIattributes\fB ) |
| 819 | .R |
| 820 | .DE |
| 821 | In the first case, |
| 822 | .I leftside |
| 823 | can denote a variable, array, array element, or structure member. |
| 824 | The value of |
| 825 | .B sizeof |
| 826 | is an integer, which gives the size in arbitrary units. |
| 827 | If the size is needed in terms of the size of some specific unit, this |
| 828 | can be computed by division: |
| 829 | .DS B |
| 830 | .B |
| 831 | sizeof(x) / sizeof(integer) |
| 832 | .R |
| 833 | .DE |
| 834 | yields the size of the variable |
| 835 | .B x |
| 836 | in integer words. |
| 837 | .PP |
| 838 | The distance between consecutive elements of an array may not equal |
| 839 | .B sizeof |
| 840 | because certain data types require final padding on some machines. |
| 841 | The |
| 842 | .B lengthof |
| 843 | operator gives this larger value, again in arbitrary units. |
| 844 | The syntax is |
| 845 | .DS B |
| 846 | \fBlengthof ( \fIleftside\fB ) |
| 847 | \fBlengthof ( \fIattributes\fB ) |
| 848 | .R |
| 849 | .DE |
| 850 | .NH 2 |
| 851 | Parentheses |
| 852 | .PP |
| 853 | An expression surrounded by parentheses is itself an expression. |
| 854 | A parenthesized expression must be evaluated before an expression of which it is a part is evaluated. |
| 855 | .NH 2 |
| 856 | Unary Operators |
| 857 | .PP |
| 858 | All of the unary operators in EFL are prefix operators. |
| 859 | The result of a unary operator has the same type as its operand. |
| 860 | .NH 3 |
| 861 | Arithmetic |
| 862 | .PP |
| 863 | Unary |
| 864 | .B + |
| 865 | has no effect. |
| 866 | A unary |
| 867 | .B \- |
| 868 | yields the negative of its operand. |
| 869 | .PP |
| 870 | The prefix operator |
| 871 | .B ++ |
| 872 | adds one to its operand. |
| 873 | The prefix operator |
| 874 | .B \-\- |
| 875 | subtracts one from its operand. |
| 876 | The value of either expression is the result of the addition or subtraction. |
| 877 | For these two operators, the operand must be a scalar, |
| 878 | array element, or structure member of arithmetic type. |
| 879 | (As a side effect, the operand value is changed.) |
| 880 | .NH 3 |
| 881 | Logical |
| 882 | .PP |
| 883 | The only logical unary operator is complement |
| 884 | (\fB\*~\fR). |
| 885 | This operator is defined by the equations |
| 886 | .DS B |
| 887 | .B |
| 888 | \*~ true = false |
| 889 | \*~ false = true |
| 890 | .R |
| 891 | .DE |
| 892 | .NH 2 |
| 893 | Binary Operators |
| 894 | .PP |
| 895 | Most EFL operators have two operands, separated by the operator. |
| 896 | Because the character set must be limited, |
| 897 | some of the operators are denoted by strings of two or three special characters. |
| 898 | All binary operators except exponentiation are left associative. |
| 899 | .NH 3 |
| 900 | Arithmetic |
| 901 | .PP |
| 902 | The binary arithmetic operators are |
| 903 | .KS |
| 904 | .TS |
| 905 | center; |
| 906 | ll. |
| 907 | + addition |
| 908 | @-@ subtraction |
| 909 | \(** multiplication |
| 910 | / division |
| 911 | \(**\(** exponentiation |
| 912 | .TE |
| 913 | .KE |
| 914 | Exponentiation is right associative: |
| 915 | a\(**\(**b\(**\(**c = a\(**\(**(b\(**\(**c) = @a sup {(b sup c )}@ |
| 916 | The operations have the conventional meanings: |
| 917 | @8+2~=~10@, |
| 918 | @8-2 ~=~ 6@, |
| 919 | @8\(** 2 ~=~ 16@, |
| 920 | @8/2~=~ 4@, |
| 921 | @8 \(**\(** 2 ~=~ 8 sup 2 ~=~ 64@. |
| 922 | .PP |
| 923 | The type of the result of a binary operation |
| 924 | @A~op~B@ |
| 925 | is determined by the types of its operands: |
| 926 | .KS |
| 927 | .TS |
| 928 | center; |
| 929 | l|lllll . |
| 930 | Type of B |
| 931 | .sp .5 |
| 932 | Type of A integer real long real complex long complex |
| 933 | _ |
| 934 | integer integer real long real complex long complex |
| 935 | real real real long real complex long complex |
| 936 | long real long real long real long real long complex long complex |
| 937 | complex complex complex long complex complex long complex |
| 938 | long complex long complex long complex long complex long complex long complex |
| 939 | .TE |
| 940 | .KE |
| 941 | If the type of an operand differs from the type of the result, |
| 942 | the calculation is done as if the operand were first coerced to the type of the result. |
| 943 | If both operands are integers, the result is of type integer, and is computed exactly. |
| 944 | (Quotients are truncated toward zero, so |
| 945 | @8/3 = 2@.) |
| 946 | .NH 3 |
| 947 | Logical |
| 948 | .PP |
| 949 | The two binary logical operations in EFL, |
| 950 | .B and |
| 951 | and |
| 952 | .B or, |
| 953 | are defined by the truth tables: |
| 954 | .KS |
| 955 | .TS |
| 956 | center; |
| 957 | cccc |
| 958 | aaaa . |
| 959 | A B A and B A or B |
| 960 | _ |
| 961 | false false false false |
| 962 | false true false true |
| 963 | true false false true |
| 964 | true true true true |
| 965 | .R |
| 966 | .TE |
| 967 | .R |
| 968 | .KE |
| 969 | Each of these operators comes in two forms. |
| 970 | In one form, the order of evaluation is specified. |
| 971 | The expression |
| 972 | .DS C |
| 973 | .B |
| 974 | a && b |
| 975 | .R |
| 976 | .DE |
| 977 | is evaluated by first evaluating |
| 978 | .B a ; |
| 979 | if it is false then the expression is false and |
| 980 | .B b |
| 981 | is not evaluated; |
| 982 | otherwise the expression has the value of |
| 983 | .B b. |
| 984 | The expression |
| 985 | .DS C |
| 986 | .B |
| 987 | a |\|| b |
| 988 | .R |
| 989 | .DE |
| 990 | is evaluated by first evaluating |
| 991 | .B a; |
| 992 | if it is true then the expression is true and |
| 993 | .B b |
| 994 | is not evaluated; |
| 995 | otherwise the expression has the value of |
| 996 | .B b. |
| 997 | The other forms of the operators |
| 998 | (\fB&\fR for \fBand\fR and \fB|\fR for \fBor\fR) |
| 999 | do not imply an order of evaluation. |
| 1000 | With the latter operators, |
| 1001 | the compiler may speed up the code by |
| 1002 | evaluating the operands in any order. |
| 1003 | .NH 3 |
| 1004 | Relational Operators |
| 1005 | .PP |
| 1006 | There are six relations between arithmetic quantities. |
| 1007 | These operators are not associative. |
| 1008 | .KS |
| 1009 | .TS |
| 1010 | center; |
| 1011 | ccs |
| 1012 | lll. |
| 1013 | EFL Operator Meaning |
| 1014 | _ |
| 1015 | < < less than |
| 1016 | <= @<=@ less than or equal to |
| 1017 | == @=@ equal to |
| 1018 | \*~= @!=@ not equal to |
| 1019 | > > greater than |
| 1020 | >= @>=@ greater than or equal |
| 1021 | .TE |
| 1022 | .KE |
| 1023 | Since the complex numbers are not ordered, the only relational operators that may take complex operands |
| 1024 | are |
| 1025 | \fB==\fR |
| 1026 | and |
| 1027 | \fB\*~=\fR . |
| 1028 | The character collating sequence is not defined. |
| 1029 | .NH 3 |
| 1030 | Assignment Operators |
| 1031 | .PP |
| 1032 | All of the assignment operators are right associative. |
| 1033 | The simple form of assignment is |
| 1034 | .DS C |
| 1035 | \fIbasic-left-side \fB= \fIexpression\fR |
| 1036 | .DE |
| 1037 | A |
| 1038 | .I basic-left-side |
| 1039 | is a scalar variable name, array element, or structure member of basic type. |
| 1040 | This statement computes the expression on the right side, and stores that value |
| 1041 | (possibly after coercing the value to the type of the left side) |
| 1042 | in the location named by the left side. |
| 1043 | The value of the assignment expression is the value assigned to the left side after coercion. |
| 1044 | .PP |
| 1045 | There is also an assignment operator corresponding to each binary arithmetic and logical operator. |
| 1046 | In each case, |
| 1047 | @a ~op = ~ b@ |
| 1048 | is equivalent to |
| 1049 | @a ~=~ a ~ op~ b@. |
| 1050 | (The operator and equal sign must not be separated by blanks.) |
| 1051 | Thus, |
| 1052 | .B n+=2 |
| 1053 | adds 2 to n. |
| 1054 | The location of the left side is evaluated only once. |
| 1055 | .NH 2 |
| 1056 | Dynamic Structures |
| 1057 | .PP |
| 1058 | EFL does not have an address (pointer, reference) type. |
| 1059 | However, there is a notation for dynamic structures, |
| 1060 | .DS B |
| 1061 | \fIleftside \fB\-> \fIstructurename\fR |
| 1062 | .DE |
| 1063 | This expression is a structure with the shape implied by |
| 1064 | .I structurename |
| 1065 | but starting at the location of |
| 1066 | .I leftside. |
| 1067 | In effect, this overlays the structure template at the specified location. |
| 1068 | The |
| 1069 | .I leftside |
| 1070 | must be a variable, array, array element, or structure member. |
| 1071 | The type of the |
| 1072 | .I leftside |
| 1073 | must be one of the types in the structure declaration. |
| 1074 | An element of such a structure is denoted in the usual way using the dot operator. |
| 1075 | Thus, |
| 1076 | .DS C |
| 1077 | .B |
| 1078 | place(i) \-> st.elt |
| 1079 | .R |
| 1080 | .DE |
| 1081 | refers to the |
| 1082 | .B elt |
| 1083 | member of the |
| 1084 | .B st |
| 1085 | structure starting at the |
| 1086 | @i sup th@ |
| 1087 | element of the array |
| 1088 | .B place. |
| 1089 | .NH 2 |
| 1090 | Repetition Operator |
| 1091 | .PP |
| 1092 | Inside of a list, an element of the form |
| 1093 | .DS C |
| 1094 | \fIinteger-constant-expression \fB$\fI constant-expression\fR |
| 1095 | .DE |
| 1096 | is equivalent to the appearance of the |
| 1097 | .I expression |
| 1098 | a number of times equal to the first expression. |
| 1099 | Thus, |
| 1100 | .DS C |
| 1101 | .B |
| 1102 | (3, 3$4, 5) |
| 1103 | .R |
| 1104 | .DE |
| 1105 | is equivalent to |
| 1106 | .DS C |
| 1107 | .B |
| 1108 | (3, 4, 4, 4, 5) |
| 1109 | .R |
| 1110 | .DE |
| 1111 | .NH 2 |
| 1112 | Constant Expressions |
| 1113 | .PP |
| 1114 | If an expression is built up out of operators (other than functions) and constants, |
| 1115 | the value of the expression is a constant, and may be used anywhere a constant is required. |
| 1116 | .NH 1 |
| 1117 | DECLARATIONS |
| 1118 | .PP |
| 1119 | Declarations statement describe the meaning, shape, and size of named |
| 1120 | objects in the EFL language. |
| 1121 | .NH 2 |
| 1122 | Syntax |
| 1123 | .PP |
| 1124 | A declaration statement is made up of attributes and variables. |
| 1125 | Declaration statements are of two form: |
| 1126 | .DS B |
| 1127 | .I |
| 1128 | attributes variable-list |
| 1129 | attributes { declarations } |
| 1130 | .R |
| 1131 | .DE |
| 1132 | In the first case, each name in the |
| 1133 | .I variable-list |
| 1134 | has the specified attributes. |
| 1135 | In the second, each name in the declarations also has the specified attributes. |
| 1136 | A variable name may appear in more than one variable list, |
| 1137 | so long as the attributes are not contradictory. |
| 1138 | Each name of a nonargument variable may be accompanied by an initial value specification. |
| 1139 | The |
| 1140 | .I declarations |
| 1141 | inside the braces are one or more declaration statements. |
| 1142 | Examples of declarations are |
| 1143 | .DS B |
| 1144 | .B |
| 1145 | integer k=2 |
| 1146 | .sp .5 |
| 1147 | long real b(7,3) |
| 1148 | .sp .5 |
| 1149 | common(cname) |
| 1150 | { |
| 1151 | integer i |
| 1152 | long real array(5,0:3) x, y |
| 1153 | character(7) ch |
| 1154 | } |
| 1155 | .R |
| 1156 | .DE |
| 1157 | .ne 1i |
| 1158 | .NH 2 |
| 1159 | Attributes |
| 1160 | .NH 3 |
| 1161 | Basic Types |
| 1162 | .PP |
| 1163 | The following are basic types in declarations |
| 1164 | .DS |
| 1165 | .B |
| 1166 | logical |
| 1167 | integer |
| 1168 | field(@m:n@) |
| 1169 | character(@k@) |
| 1170 | real |
| 1171 | complex |
| 1172 | .R |
| 1173 | .DE |
| 1174 | In the above, the quantities @k@, @m@, and @n@ denote integer constant expressions with the properties |
| 1175 | @k>0@ and @n>m@. |
| 1176 | .NH 3 |
| 1177 | Arrays |
| 1178 | .PP |
| 1179 | The dimensionality may be declared by an |
| 1180 | .B array |
| 1181 | attribute |
| 1182 | .EQ C |
| 1183 | bold array( b sub 1 , ..., b sub n bold ) |
| 1184 | .EN |
| 1185 | Each of the @b sub i@ |
| 1186 | may either be a single integer expression or a pair of integer expressions separated by a colon. |
| 1187 | The pair of expressions form a lower and an upper bound; the single expression is an upper bound with |
| 1188 | an implied lower bound of 1. |
| 1189 | The number of dimensions is equal to |
| 1190 | @n,@ |
| 1191 | the number of bounds. |
| 1192 | All of the integer expressions must be constants. |
| 1193 | An exception is permitted only if all of the variables associated with an |
| 1194 | array declarator are formal arguments of the procedure; in this case, each bound |
| 1195 | must have the property that |
| 1196 | @upper - lower + 1@ |
| 1197 | is equal to a formal argument of the procedure. |
| 1198 | (The compiler has limited ability to simplify expressions, but it will recognize |
| 1199 | important cases such as |
| 1200 | .B "(0:n\-1)". |
| 1201 | The upper bound for the last dimension |
| 1202 | @(b sub n )@ |
| 1203 | may be marked by an asterisk |
| 1204 | ( \fB\(**\fR ) |
| 1205 | if the size of the array is not known. |
| 1206 | The following are legal @bold array@ attributes: |
| 1207 | .DS B |
| 1208 | .B |
| 1209 | array(5) |
| 1210 | array(5, 1:5, \-3:0) |
| 1211 | array(5, \(**) |
| 1212 | array(0:m\-1, m) |
| 1213 | .R |
| 1214 | .DE |
| 1215 | .NH 3 |
| 1216 | Structures |
| 1217 | .PP |
| 1218 | A structure declaration is of the form |
| 1219 | .DS B |
| 1220 | \fBstruct \fIstructname \fB{ \fI declaration statements \fB}\fR |
| 1221 | .DE |
| 1222 | The |
| 1223 | .I structname |
| 1224 | is optional; if it is present, it acts as if it were the name of a type in the rest of its scope. |
| 1225 | Each name that appears inside the |
| 1226 | .I declarations |
| 1227 | is a |
| 1228 | .I member |
| 1229 | of the structure, and has a special meaning when used to qualify any variable declared with the structure type. |
| 1230 | A name may appear as a member of any number of structures, |
| 1231 | and may also be the name of an ordinary variable, |
| 1232 | since a structure member name is used only in contexts where the parent type is known. |
| 1233 | The following are valid structure attributes |
| 1234 | .DS B |
| 1235 | .B |
| 1236 | struct xx |
| 1237 | { |
| 1238 | integer a, b |
| 1239 | real x(5) |
| 1240 | } |
| 1241 | |
| 1242 | struct { xx z(3); character(5) y } |
| 1243 | .R |
| 1244 | .DE |
| 1245 | The last line defines a structure containing an array of three @bold xx 's@ |
| 1246 | and a character string. |
| 1247 | .NH 3 |
| 1248 | Precision |
| 1249 | .PP |
| 1250 | Variables of floating point |
| 1251 | (@bold real@ or @bold complex@) type may be declared to be |
| 1252 | @bold long@ |
| 1253 | to ensure they have higher precision than ordinary floating point variables. |
| 1254 | The default precision is |
| 1255 | \fBshort\fR. |
| 1256 | .NH 3 |
| 1257 | Common |
| 1258 | .PP |
| 1259 | Certain objects called |
| 1260 | .I common\ areas |
| 1261 | have external scope, |
| 1262 | and may be referenced by any procedure that has a declaration for the name using a |
| 1263 | .DS C |
| 1264 | \fBcommon ( \fI commonareaname \fB)\fR |
| 1265 | .DE |
| 1266 | attribute. |
| 1267 | All of the variables declared with a particular \fBcommon\fR attribute are in the same |
| 1268 | block; the order in which they are declared is significant. |
| 1269 | Declarations for the same block in differing procedures must have the variables in the same order and with the |
| 1270 | same types, precision, and shapes, though not necessarily with the same names. |
| 1271 | .NH 3 |
| 1272 | External |
| 1273 | .PP |
| 1274 | If a name is used as the procedure name in a procedure invocation, |
| 1275 | it is implicitly declared to have the |
| 1276 | .B external |
| 1277 | attribute. |
| 1278 | If a procedure name is to be passed as an argument, it is necessary to declare |
| 1279 | it in a statement of the form |
| 1280 | .DS B |
| 1281 | \fBexternal \*([[ \fIname \fB\*(]]\fR |
| 1282 | .DE |
| 1283 | If a name has the external attribute and it is a formal argument of |
| 1284 | the procedure, |
| 1285 | then it is associated with a procedure identifier passed as an actual argument |
| 1286 | at each call. |
| 1287 | If the name is not a formal argument, then that name is the actual name |
| 1288 | of a procedure, as it appears in the corresponding |
| 1289 | .B procedure |
| 1290 | statement. |
| 1291 | .NH 2 |
| 1292 | Variable List |
| 1293 | .PP |
| 1294 | The elements of a variable list in a declaration |
| 1295 | consist of a name, |
| 1296 | an optional dimension specification, |
| 1297 | and an optional initial value specification. |
| 1298 | The name follows the usual rules. |
| 1299 | The dimension specification is the same form and meaning as the parenthesized list in an |
| 1300 | .B array |
| 1301 | attribute. |
| 1302 | The initial value specification is an equal sign (\fB=\fR) followed by a constant expression. |
| 1303 | If the name is an array, the right side of the equal sign may be a parenthesized list of constant expressions, |
| 1304 | or repeated elements or lists; the total number of elements in the list must not exceed the number of elements of the |
| 1305 | array, which are filled in column-major order. |
| 1306 | .NH 2 |
| 1307 | The Initial Statement |
| 1308 | .PP |
| 1309 | An initial value may also be specified for a simple variable, |
| 1310 | array, array element, or member of a structure |
| 1311 | using a statement of the form |
| 1312 | .DS B |
| 1313 | \fBinitial \*([[ \fIvar \fB= \fIval \*(]]\fR |
| 1314 | .DE |
| 1315 | The @var@ may be a variable name, array element specification, or member of structure. |
| 1316 | The right side follows the same rules as for an initial value specification |
| 1317 | in other declaration statements. |
| 1318 | .NH 1 |
| 1319 | EXECUTABLE STATEMENTS |
| 1320 | .PP |
| 1321 | Every useful EFL program contains executable statements \(em |
| 1322 | otherwise it would not do anything and would not need to be run. |
| 1323 | Statements are frequently made up of other statements. |
| 1324 | Blocks are the most obvious case, |
| 1325 | but many other forms contain statements as constituents. |
| 1326 | .PP |
| 1327 | To increase the legibility of EFL programs, |
| 1328 | some of the statement forms can be broken without an explicit continuation. |
| 1329 | A square (\fR\(sq\fP) in the syntax represents a point where the end of a line will be ignored. |
| 1330 | .NH 2 |
| 1331 | Expression Statements |
| 1332 | .NH 3 |
| 1333 | Subroutine Call |
| 1334 | .PP |
| 1335 | A procedure invocation that returns no value is known as a subroutine call. |
| 1336 | Such an invocation is a statement. |
| 1337 | Examples are |
| 1338 | .DS B |
| 1339 | .B |
| 1340 | work(in, out) |
| 1341 | run(\|) |
| 1342 | .R |
| 1343 | .DE |
| 1344 | .PP |
| 1345 | Input/output statements (see Section 7.7) |
| 1346 | resemble procedure invocations |
| 1347 | but do not yield a value. |
| 1348 | If an error occurs |
| 1349 | the program stops. |
| 1350 | .NH 3 |
| 1351 | Assignment Statements |
| 1352 | .PP |
| 1353 | An expression that is a simple assignment (\fB=\fR) or |
| 1354 | a compound assignment (\fB+=\fR etc.) is a statement: |
| 1355 | .DS B |
| 1356 | .B |
| 1357 | a = b |
| 1358 | a = sin(x)/6 |
| 1359 | x \(**= y |
| 1360 | .R |
| 1361 | .DE |
| 1362 | .NH 2 |
| 1363 | Blocks |
| 1364 | .PP |
| 1365 | A block is a compound statement that acts as a statement. |
| 1366 | A block begins with a left brace, |
| 1367 | optionally followed by declarations, |
| 1368 | optionally followed by executable statements, |
| 1369 | followed by a right brace. |
| 1370 | A block may be used anywhere a statement is permitted. |
| 1371 | A block is not an expression and does not have a value. |
| 1372 | An example of a block is |
| 1373 | .DS B |
| 1374 | .B |
| 1375 | { |
| 1376 | integer i # this variable is unknown outside the braces |
| 1377 | .sp .3 |
| 1378 | big = 0 |
| 1379 | do i = 1,n |
| 1380 | if(big < a(i)) |
| 1381 | big = a(i) |
| 1382 | } |
| 1383 | .R |
| 1384 | .DE |
| 1385 | .NH 2 |
| 1386 | Test Statements |
| 1387 | .PP |
| 1388 | Test statements permit execution of certain statements conditional on the truth of a predicate. |
| 1389 | .NH 3 |
| 1390 | If Statement |
| 1391 | .PP |
| 1392 | The simplest of the test statements is the |
| 1393 | .B if |
| 1394 | statement, of form |
| 1395 | .DS C |
| 1396 | \fBif ( \fIlogical-expression\fB ) \fR\(sq\fP \fIstatement\fR |
| 1397 | .DE |
| 1398 | The logical expression is evaluated; |
| 1399 | if it is true, then the |
| 1400 | .I statement |
| 1401 | is executed. |
| 1402 | .NH 3 |
| 1403 | If-Else |
| 1404 | .PP |
| 1405 | A more general statement is of the form |
| 1406 | .DS B |
| 1407 | \fBif ( \fIlogical-expression \fB) \fR\(sq\fP \fI statement-1 \fR\(sq\fP \fBelse \fR\(sq\fP \fI statement-2 \fR |
| 1408 | .DE |
| 1409 | If the expression is |
| 1410 | .B true |
| 1411 | then |
| 1412 | .I statement-1 |
| 1413 | is executed, otherwise |
| 1414 | .I statement-2 |
| 1415 | is executed. |
| 1416 | Either of the consequent statements may itself be an |
| 1417 | .B if-else |
| 1418 | so a completely nested test sequence is possible: |
| 1419 | .DS B |
| 1420 | .B |
| 1421 | if(x<y) |
| 1422 | if(a<b) |
| 1423 | k = 1 |
| 1424 | else |
| 1425 | k = 2 |
| 1426 | else |
| 1427 | if(a<b) |
| 1428 | m = 1 |
| 1429 | else |
| 1430 | m = 2 |
| 1431 | .R |
| 1432 | .DE |
| 1433 | An |
| 1434 | .B else |
| 1435 | applies to the nearest preceding un-\fBelse\fRd \fBif\fR. |
| 1436 | A more common use is as a sequential test: |
| 1437 | .DS B |
| 1438 | .B |
| 1439 | if(x==1) |
| 1440 | k = 1 |
| 1441 | else if(x==3 | x==5) |
| 1442 | k = 2 |
| 1443 | else |
| 1444 | k = 3 |
| 1445 | .R |
| 1446 | .DE |
| 1447 | .NH 3 |
| 1448 | Select Statement |
| 1449 | .PP |
| 1450 | A multiway test on the value of a quantity is succinctly stated as a |
| 1451 | .B select |
| 1452 | statement, which has the general form |
| 1453 | .DS B |
| 1454 | \fBselect( \fIexpression\fB ) \fR\(sq\fP \fIblock\fR |
| 1455 | .DE |
| 1456 | Inside the block |
| 1457 | two special types of labels are recognized. |
| 1458 | A prefix of the form |
| 1459 | .DS B |
| 1460 | \fBcase \fI\*([[ constant \*(]] \fB:\fR |
| 1461 | .DE |
| 1462 | marks the statement to which control is passed if the |
| 1463 | expression |
| 1464 | in the select has a value equal to one of the case constants. |
| 1465 | If the expression equals none of these constants, but there is |
| 1466 | a label |
| 1467 | .B default |
| 1468 | inside the select, |
| 1469 | a branch is taken to that point; |
| 1470 | otherwise the statement following the right brace is executed. |
| 1471 | Once execution begins at a |
| 1472 | .B case |
| 1473 | or |
| 1474 | .B default |
| 1475 | label, it continues until the next |
| 1476 | .B case |
| 1477 | or |
| 1478 | .B default |
| 1479 | is encountered. |
| 1480 | The |
| 1481 | .B else-if |
| 1482 | example above is better written as |
| 1483 | .DS B |
| 1484 | .B |
| 1485 | select(x) |
| 1486 | { |
| 1487 | case 1: |
| 1488 | k = 1 |
| 1489 | case 3,5: |
| 1490 | k = 2 |
| 1491 | default: |
| 1492 | k = 3 |
| 1493 | } |
| 1494 | .R |
| 1495 | .DE |
| 1496 | Note that control does not `fall through' to the next case. |
| 1497 | .NH 2 |
| 1498 | Loops |
| 1499 | .PP |
| 1500 | The loop forms provide the best way of repeating a statement |
| 1501 | or sequence of operations. |
| 1502 | The simplest (\fBwhile\fR) form is theoretically sufficient, but it is very convenient to have |
| 1503 | the more general loops available, since each expresses a mode of control |
| 1504 | that arises frequently in practice. |
| 1505 | .NH 3 |
| 1506 | While Statement |
| 1507 | .PP |
| 1508 | This construct has the form |
| 1509 | .DS C |
| 1510 | \fBwhile ( \fIlogical-expression\fB ) \fR\(sq\fP \fIstatement\fR |
| 1511 | .DE |
| 1512 | The expression is evaluated; if it is true, the statement is executed, and then the test is performed again. |
| 1513 | If the expression is false, execution proceeds to the next statement. |
| 1514 | .NH 2 |
| 1515 | For Statement |
| 1516 | .PP |
| 1517 | The |
| 1518 | .B for |
| 1519 | statement is a more elaborate looping construct. |
| 1520 | It has the form |
| 1521 | .DS C |
| 1522 | \fBfor ( \fIinitial-statement \fB, \fR\(sq\fP \fIlogical-expression \fB, \fR\(sq\fP \fI iteration-statement \fB) \fR\(sq\fP \fIbody-statement |
| 1523 | .DE |
| 1524 | Except for the behavior of the |
| 1525 | .B next |
| 1526 | statement (see Section 7.6.3), this construct is equivalent to |
| 1527 | .DS B |
| 1528 | \fIinitial-statement |
| 1529 | \fBwhile ( \fIlogical-expression\fB ) |
| 1530 | { |
| 1531 | \fIbody-statement |
| 1532 | \fIiteration-statement |
| 1533 | } |
| 1534 | .DE |
| 1535 | This form is useful for general arithmetic iterations, and for various pointer-type operations. |
| 1536 | The sum of the integers from 1 to 100 can be computed by the fragment |
| 1537 | .DS B |
| 1538 | .B |
| 1539 | n = 0 |
| 1540 | for(i = 1, i <= 100, i += 1) |
| 1541 | n += i |
| 1542 | .R |
| 1543 | .DE |
| 1544 | Alternatively, the computation could be done by the single statement |
| 1545 | .DS B |
| 1546 | .B |
| 1547 | for( { n = 0 ; i = 1 } , i<=100 , { n += i ; ++i } ) |
| 1548 | ; |
| 1549 | .R |
| 1550 | .DE |
| 1551 | Note that the body of the |
| 1552 | .B for |
| 1553 | loop is a null statement in this case. |
| 1554 | An example of following a linked list will be given later. |
| 1555 | .NH 3 |
| 1556 | Repeat Statement |
| 1557 | .PP |
| 1558 | The statement |
| 1559 | .DS B |
| 1560 | \fBrepeat \fR\(sq\fP \fIstatement\fR |
| 1561 | .DE |
| 1562 | executes the statement, then does it again, without any termination test. |
| 1563 | Obviously, a test inside the |
| 1564 | .I statement |
| 1565 | is needed to stop the loop. |
| 1566 | .NH 3 |
| 1567 | Repeat...Until Statement |
| 1568 | .PP |
| 1569 | The |
| 1570 | .B while |
| 1571 | loop performs a test before each iteration. |
| 1572 | The statement |
| 1573 | .DS B |
| 1574 | \fBrepeat \fR\(sq \fIstatement \fR\(sq \fBuntil ( \fIlogical-expression \fB) |
| 1575 | .DE |
| 1576 | executes the |
| 1577 | .I statement, |
| 1578 | then evaluates the logical; |
| 1579 | if the logical is |
| 1580 | true the loop is complete; |
| 1581 | otherwise control returns to the |
| 1582 | .I statement. |
| 1583 | Thus, the body is always executed at least once. |
| 1584 | The |
| 1585 | .B until |
| 1586 | refers to the nearest preceding |
| 1587 | .B repeat |
| 1588 | that has not been paired with an |
| 1589 | .B until. |
| 1590 | In practice, this appears to be the least frequently used looping construct. |
| 1591 | .NH 3 |
| 1592 | Do Loops |
| 1593 | .PP |
| 1594 | The simple arithmetic progression is a very common one in numerical applications. |
| 1595 | EFL has a special loop form for ranging over an ascending arithmetic sequence |
| 1596 | .DS B |
| 1597 | \fBdo \fIvariable \fB= \fIexpression-1, expression-2, expression-3\fR |
| 1598 | \fIstatement\fR |
| 1599 | .DE |
| 1600 | The variable is first given the value |
| 1601 | .I expression-1. |
| 1602 | The statement is executed, then |
| 1603 | .I expression-3 |
| 1604 | is added to the variable. |
| 1605 | The loop is repeated until the variable exceeds |
| 1606 | .I expression-2. |
| 1607 | If |
| 1608 | .I expression-3 |
| 1609 | and the preceding comma are omitted, the increment is taken to be 1. |
| 1610 | The loop above is equivalent to |
| 1611 | .DS B |
| 1612 | t2 = expression-2 |
| 1613 | t3 = expression-3 |
| 1614 | for(variable = expression-1 , variable <= t2 , variable += t3) |
| 1615 | statement |
| 1616 | .DE |
| 1617 | (The compiler translates EFL |
| 1618 | .B do |
| 1619 | statements into Fortran |
| 1620 | DO statements, |
| 1621 | which are in turn usually compiled into excellent code.) |
| 1622 | The |
| 1623 | .B do |
| 1624 | .I variable |
| 1625 | may not be changed inside of the loop, |
| 1626 | and |
| 1627 | .I expression-1 |
| 1628 | must not exceed |
| 1629 | .I expression-2. |
| 1630 | The sum of the first hundred positive integers could be computed by |
| 1631 | .DS B |
| 1632 | .B |
| 1633 | n = 0 |
| 1634 | do i = 1, 100 |
| 1635 | n += i |
| 1636 | .R |
| 1637 | .DE |
| 1638 | .NH 2 |
| 1639 | Branch Statements |
| 1640 | .PP |
| 1641 | Most of the need for branch statements in programs can be |
| 1642 | averted by using the loop and test constructs, |
| 1643 | but there are programs where they are very useful. |
| 1644 | .NH 3 |
| 1645 | Goto Statement |
| 1646 | .PP |
| 1647 | The most general, and most dangerous, branching statement is the simple unconditional |
| 1648 | .DS B |
| 1649 | \fBgoto \fIlabel\fR |
| 1650 | .DE |
| 1651 | After executing this statement, the next statement performed is the one following the given label. |
| 1652 | Inside of a |
| 1653 | .B select |
| 1654 | the case labels of that block may be used as labels, as in the following example: |
| 1655 | .KS |
| 1656 | .B |
| 1657 | .TS |
| 1658 | center; |
| 1659 | lll . |
| 1660 | select(k) |
| 1661 | { |
| 1662 | case 1: |
| 1663 | error(7) |
| 1664 | |
| 1665 | case 2: |
| 1666 | k = 2 |
| 1667 | goto case 4 |
| 1668 | |
| 1669 | case 3: |
| 1670 | k = 5 |
| 1671 | goto case 4 |
| 1672 | |
| 1673 | case 4: |
| 1674 | fixup(k) |
| 1675 | goto default |
| 1676 | |
| 1677 | default: |
| 1678 | prmsg("ouch") |
| 1679 | } |
| 1680 | .TE |
| 1681 | .KE |
| 1682 | .R |
| 1683 | (If two |
| 1684 | .B select |
| 1685 | statements are nested, |
| 1686 | the case labels of the outer |
| 1687 | .B select |
| 1688 | are not accessible from the inner one.) |
| 1689 | .NH 3 |
| 1690 | Break Statement |
| 1691 | .PP |
| 1692 | A safer statement is one which transfers control to the statement following the current |
| 1693 | .B select |
| 1694 | or loop form. |
| 1695 | A statement of this sort is almost always needed in a |
| 1696 | .B repeat |
| 1697 | loop: |
| 1698 | .DS B |
| 1699 | .B |
| 1700 | repeat |
| 1701 | { |
| 1702 | \fIdo a computation |
| 1703 | if\|( finished ) |
| 1704 | \fBbreak\fI |
| 1705 | } |
| 1706 | .R |
| 1707 | .DE |
| 1708 | More general forms permit controlling a branch out of more than one construct. |
| 1709 | .DS C |
| 1710 | .B |
| 1711 | break 3 |
| 1712 | .R |
| 1713 | .DE |
| 1714 | transfers control to the statement following the third loop and/or |
| 1715 | .B select |
| 1716 | surrounding the statement. |
| 1717 | It is possible to specify which type of construct |
| 1718 | (\fBfor\fR, \fBwhile\fR, \fBrepeat\fR, \fBdo\fR, or \fBselect\fR) |
| 1719 | is to be counted. |
| 1720 | The statement |
| 1721 | .DS C |
| 1722 | .B |
| 1723 | break while |
| 1724 | .R |
| 1725 | .DE |
| 1726 | breaks out of the first surrounding |
| 1727 | .B while |
| 1728 | statement. |
| 1729 | Either of the statements |
| 1730 | .DS B |
| 1731 | .B |
| 1732 | break 3 for |
| 1733 | break for 3 |
| 1734 | .R |
| 1735 | .DE |
| 1736 | will transfer to the statement after the third enclosing |
| 1737 | .B for |
| 1738 | loop. |
| 1739 | .NH 3 |
| 1740 | Next Statement |
| 1741 | .PP |
| 1742 | The |
| 1743 | .B next |
| 1744 | statement causes the first surrounding loop statement to go on to the next iteration: |
| 1745 | the next operation performed is the |
| 1746 | test of a |
| 1747 | .B while, |
| 1748 | the |
| 1749 | .I iteration-statement |
| 1750 | of a |
| 1751 | .B for, |
| 1752 | the body of a |
| 1753 | .B repeat, |
| 1754 | the test of a |
| 1755 | .B repeat...until, |
| 1756 | or the increment of a |
| 1757 | .B do. |
| 1758 | Elaborations similar to those for |
| 1759 | .B break |
| 1760 | are available: |
| 1761 | .DS B |
| 1762 | .B |
| 1763 | next |
| 1764 | next 3 |
| 1765 | next 3 for |
| 1766 | next for 3 |
| 1767 | .R |
| 1768 | .DE |
| 1769 | A |
| 1770 | .B next |
| 1771 | statement ignores |
| 1772 | .B select |
| 1773 | statements. |
| 1774 | .NH 3 |
| 1775 | Return |
| 1776 | .PP |
| 1777 | The last statement of a procedure is followed by a return of control to the caller. |
| 1778 | If it is desired to effect such a return from any other point in the procedure, a |
| 1779 | .DS B |
| 1780 | \fBreturn\fR |
| 1781 | .DE |
| 1782 | statement may be executed. |
| 1783 | Inside a function procedure, the function value is specified as an argument of the statement: |
| 1784 | .DS B |
| 1785 | \fBreturn ( \fIexpression \fB) |
| 1786 | .DE |
| 1787 | .NH 2 |
| 1788 | Input/Output Statements |
| 1789 | .PP |
| 1790 | EFL has two input statements (\fBread\fR and \fBreadbin\fR), |
| 1791 | two output statements (\fBwrite\fR and \fBwritebin\fR), |
| 1792 | and three control statements (\fBendfile\fR, \fBrewind\fR, and \fBbackspace\fR). |
| 1793 | These forms may be used either as a primary with a |
| 1794 | .B integer |
| 1795 | value |
| 1796 | or as a statement. |
| 1797 | If an exception occurs when one of these forms is used as a statement, |
| 1798 | the result is undefined but will probably be treated as a fatal error. |
| 1799 | If they are used in a context where they return a value, |
| 1800 | they return |
| 1801 | zero if no exception occurs. |
| 1802 | For the input forms, a negative value indicates end-of-file and |
| 1803 | a positive value an error. |
| 1804 | The input/output part of EFL very strongly reflects the facilities of Fortran. |
| 1805 | .NH 3 |
| 1806 | Input/Output Units |
| 1807 | .PP |
| 1808 | Each I/O statement refers to a `unit', |
| 1809 | identified by a small positive integer. |
| 1810 | Two special units are defined by EFL, |
| 1811 | the |
| 1812 | .I "standard input unit" |
| 1813 | and the |
| 1814 | .I "standard output unit." |
| 1815 | These particular units are assumed if no unit is specified in an I/O transmission statement. |
| 1816 | .PP |
| 1817 | The data on the unit are organized into |
| 1818 | .I records. |
| 1819 | These records may be read or written in a fixed sequence, |
| 1820 | and each transmission moves an integral number of records. |
| 1821 | Transmission proceeds from the first record until the |
| 1822 | .I "end of file." |
| 1823 | .NH 3 |
| 1824 | Binary Input/Output |
| 1825 | .PP |
| 1826 | The |
| 1827 | .B readbin |
| 1828 | and |
| 1829 | .B writebin |
| 1830 | statements transmit data in a machine-dependent but swift manner. |
| 1831 | The statements are of the form |
| 1832 | .DS B |
| 1833 | \fBwritebin( \fIunit \fB, \fIbinary-output-list \fB)\fR |
| 1834 | \fBreadbin( \fIunit \fB, \fIbinary-input-list \fB)\fR |
| 1835 | .DE |
| 1836 | Each statement moves one unformatted record between storage and the device. |
| 1837 | The |
| 1838 | .I unit |
| 1839 | is an integer expression. |
| 1840 | A |
| 1841 | .I binary-output-list |
| 1842 | is an |
| 1843 | .I iolist |
| 1844 | (see below) without any format specifiers. |
| 1845 | A |
| 1846 | .I binary-input-list |
| 1847 | is an |
| 1848 | .I iolist |
| 1849 | without format specifiers in which each of the expressions |
| 1850 | is a variable name, array element, or structure member. |
| 1851 | .NH 3 |
| 1852 | Formatted Input/Output |
| 1853 | .PP |
| 1854 | The |
| 1855 | .B read |
| 1856 | and |
| 1857 | .B write |
| 1858 | statements |
| 1859 | transmit data in the form of lines of characters. |
| 1860 | Each statement moves one or more records (lines). |
| 1861 | Numbers are translated into decimal notation. |
| 1862 | The exact form of the lines is determined by format specifications, |
| 1863 | whether provided explicitly in the statement |
| 1864 | or implicitly. |
| 1865 | The syntax of the statements is |
| 1866 | .DS B |
| 1867 | \fBwrite( \fIunit \fB,\fI formatted-output-list \fB)\fR |
| 1868 | \fBread( \fIunit \fB,\fI formatted-input-list \fB)\fR |
| 1869 | .DE |
| 1870 | The lists are of the same form as for binary I/O, |
| 1871 | except that the lists may include format specifications. |
| 1872 | If the |
| 1873 | .I unit |
| 1874 | is omitted, the standard input or output unit is used. |
| 1875 | .NH 3 |
| 1876 | Iolists |
| 1877 | .PP |
| 1878 | An |
| 1879 | .I iolist |
| 1880 | specifies a set of values to be written or a set of variables into which |
| 1881 | values are to be read. |
| 1882 | An |
| 1883 | .I iolist |
| 1884 | is a list of one or more |
| 1885 | .I ioexpressions |
| 1886 | of the form |
| 1887 | .DS B |
| 1888 | \fIexpression |
| 1889 | \fB{ \fIiolist \fB} |
| 1890 | \fIdo-specification \fB{ \fIiolist \fB}\fR |
| 1891 | .DE |
| 1892 | For formatted I/O, |
| 1893 | an |
| 1894 | .I ioexpression |
| 1895 | may also have the forms |
| 1896 | .DS B |
| 1897 | \fIioexpression \fB:\fI format-specifier |
| 1898 | \fB:\fI format-specifier\fR |
| 1899 | .DE |
| 1900 | A |
| 1901 | .I do-specification |
| 1902 | looks just like a |
| 1903 | .B do |
| 1904 | statement, and has a similar effect: |
| 1905 | the values in the braces are transmitted repeatedly until the |
| 1906 | .B do |
| 1907 | execution is complete. |
| 1908 | .NH 3 |
| 1909 | Formats |
| 1910 | .PP |
| 1911 | The following are permissible |
| 1912 | .I format-specifiers. |
| 1913 | The quantities |
| 1914 | @w@, @d@, and @k@ must be integer constant expressions. |
| 1915 | .KS |
| 1916 | .TS |
| 1917 | center; |
| 1918 | ll . |
| 1919 | \fBi(\fIw\fB)\fR integer with \fIw\fR digits |
| 1920 | \fBf(\fIw\fB,\fId\fB)\fR floating point number of \fIw\fR characters, |
| 1921 | \fId\fR of them to the right of the decimal point. |
| 1922 | \fBe(\fIw\fB,\fId\fB)\fR floating point number of \fIw\fR characters, |
| 1923 | \fId\fR of them to the right of the decimal point, |
| 1924 | with the exponent field marked with the letter \fBe\fR |
| 1925 | \fBl(\fIw\fB)\fR logical field of width \fIw\fR characters, |
| 1926 | the first of which is \fBt\fR or \fBf\fR |
| 1927 | (the rest are blank on output, ignored on input) |
| 1928 | standing for \fBtrue\fR and \fBfalse\fR respectively |
| 1929 | \fBc\fR character string of width equal to the length of the datum |
| 1930 | \fBc(\fIw\fB)\fR character string of width \fIw\fR |
| 1931 | \fBs(\fIk\fB)\fR skip \fIk\fR lines |
| 1932 | \fBx(\fIk\fB)\fR skip \fIk\fR spaces |
| 1933 | " ... " use the characters inside the string as a Fortran format |
| 1934 | .TE |
| 1935 | .KE |
| 1936 | If no format is specified for an item in a formatted input/output statement, |
| 1937 | a default form is chosen. |
| 1938 | .PP |
| 1939 | If an item in a list is an array name, |
| 1940 | then the entire array is transmitted as a sequence of elements, |
| 1941 | each with its own format. |
| 1942 | The elements are transmitted in column-major order, |
| 1943 | the same order used for array initializations. |
| 1944 | .NH 3 |
| 1945 | Manipulation statements |
| 1946 | .PP |
| 1947 | The three input/output statements |
| 1948 | .DS B |
| 1949 | .B |
| 1950 | backspace(@unit@) |
| 1951 | rewind(@unit@) |
| 1952 | endfile(@unit@) |
| 1953 | .R |
| 1954 | .DE |
| 1955 | look like ordinary procedure calls, |
| 1956 | but may be used either as statements or as integer expressions |
| 1957 | which yield |
| 1958 | non-zero |
| 1959 | if an error is detected. |
| 1960 | .B backspace |
| 1961 | causes the specified unit to back up, |
| 1962 | so that the next |
| 1963 | read will re-read the previous record, |
| 1964 | and the next write will over-write it. |
| 1965 | .B rewind |
| 1966 | moves the device to its beginning, |
| 1967 | so that the next input statement will read the first record. |
| 1968 | .B endfile |
| 1969 | causes the file to be marked so that the record most recently written will be the last record on the file, |
| 1970 | and any attempt to read past is an error. |
| 1971 | .NH 1 |
| 1972 | PROCEDURES |
| 1973 | .PP |
| 1974 | Procedures are the basic unit of an EFL program, |
| 1975 | and provide the means of segmenting a program into separately compilable |
| 1976 | and named parts. |
| 1977 | .NH 2 |
| 1978 | Procedure Statement |
| 1979 | .PP |
| 1980 | Each procedure begins with a statement of one of the forms |
| 1981 | .DS B |
| 1982 | \fBprocedure |
| 1983 | \fIattributes \fBprocedure \fIprocedurename |
| 1984 | \fIattributes \fBprocedure \fIprocedurename \fB( )\fR |
| 1985 | \fIattributes \fBprocedure \fIprocedurename \fB( \fI\*([[ name \*(]] \fB) \fR |
| 1986 | .DE |
| 1987 | The first case specifies the main procedure, where execution begins. |
| 1988 | In the two other cases, the |
| 1989 | .I attributes |
| 1990 | may specify precision and type, |
| 1991 | or they may be omitted entirely. |
| 1992 | The precision and type of the procedure may be declared in an ordinary declaration statement. |
| 1993 | If no type is declared, then the procedure is called a |
| 1994 | .I subroutine |
| 1995 | and no value may be returned for it. |
| 1996 | Otherwise, the procedure is a function and a value of the declared type is returned for each call. |
| 1997 | Each |
| 1998 | .I name |
| 1999 | inside the parentheses in the last form above is called a |
| 2000 | .I "formal argument" |
| 2001 | of the procedure. |
| 2002 | .NH 2 |
| 2003 | End Statement |
| 2004 | .PP |
| 2005 | Each procedure terminates with a statement |
| 2006 | .DS C |
| 2007 | .B |
| 2008 | end |
| 2009 | .R |
| 2010 | .DE |
| 2011 | .NH 2 |
| 2012 | Argument Association |
| 2013 | .PP |
| 2014 | When a procedure is invoked, |
| 2015 | the actual arguments are evaluated. |
| 2016 | If an actual argument is the name of a variable, an array element, |
| 2017 | or a structure member, |
| 2018 | that entity becomes associated with the formal argument, |
| 2019 | and the procedure may reference the values in the object, |
| 2020 | and assign to it. |
| 2021 | Otherwise, |
| 2022 | the value of the actual is associated with the formal argument, |
| 2023 | but the procedure may not attempt to change the value of that formal argument. |
| 2024 | .PP |
| 2025 | If the value of one of the arguments is changed in the procedure, |
| 2026 | it is not permitted that the corresponding actual argument be associated |
| 2027 | with another formal argument or with a |
| 2028 | .B common |
| 2029 | element that is referenced in the procedure. |
| 2030 | .NH 2 |
| 2031 | Execution and Return Values |
| 2032 | .PP |
| 2033 | After actual and formal arguments have been associated, |
| 2034 | control passes to the first executable statement of the procedure. |
| 2035 | Control returns to the invoker |
| 2036 | either when the |
| 2037 | .B end |
| 2038 | statement of the procedure is reached or when a |
| 2039 | .B return |
| 2040 | statement is executed. |
| 2041 | If the procedure is a function |
| 2042 | (has a declared type), |
| 2043 | and a |
| 2044 | @bold return( value )@ |
| 2045 | is executed, the value |
| 2046 | is coerced to the correct type and precision and returned. |
| 2047 | .NH 2 |
| 2048 | Known Functions |
| 2049 | .PP |
| 2050 | A number of functions are known to EFL, and need not be declared. |
| 2051 | The compiler knows the types of these functions. |
| 2052 | Some of them are |
| 2053 | .I generic; |
| 2054 | i.e., they name a family of functions that differ in the types of their arguments and return values. |
| 2055 | The compiler chooses which element of the set to invoke based upon the attributes of the actual arguments. |
| 2056 | .NH 3 |
| 2057 | Minimum and Maximum Functions |
| 2058 | .PP |
| 2059 | The generic functions are |
| 2060 | .B min |
| 2061 | and |
| 2062 | .B max. |
| 2063 | The |
| 2064 | .B min |
| 2065 | calls return the value of their smallest argument; |
| 2066 | the |
| 2067 | .B max |
| 2068 | calls return the value of their largest argument. |
| 2069 | These are the only functions that may take different numbers of arguments in different calls. |
| 2070 | If any of the arguments are |
| 2071 | .B "long real" |
| 2072 | then the result is |
| 2073 | .B "long real". |
| 2074 | Otherwise, if any of the arguments are |
| 2075 | .B real |
| 2076 | then the result is |
| 2077 | .B real; |
| 2078 | otherwise all the arguments and the result must be |
| 2079 | .B integer. |
| 2080 | Examples are |
| 2081 | .DS B |
| 2082 | .B |
| 2083 | min(5, x, \-3.20) |
| 2084 | max(i, z) |
| 2085 | .R |
| 2086 | .DE |
| 2087 | .NH 3 |
| 2088 | Absolute Value |
| 2089 | .PP |
| 2090 | The |
| 2091 | .B abs |
| 2092 | function is a generic function that returns the magnitude of its argument. |
| 2093 | For |
| 2094 | integer and real arguments the type of the result is identical to the type of the argument; |
| 2095 | for complex arguments the type of the result is the real of the same precision. |
| 2096 | .NH 3 |
| 2097 | Elementary Functions |
| 2098 | .PP |
| 2099 | The following generic functions take arguments of |
| 2100 | \fBreal\fR, \fBlong real\fR, or \fBcomplex\fR |
| 2101 | type and return a result of the same type: |
| 2102 | .DS |
| 2103 | .TS |
| 2104 | center; |
| 2105 | ll. |
| 2106 | .B |
| 2107 | sin sine function |
| 2108 | cos cosine function |
| 2109 | exp exponential function (@e sup x@). |
| 2110 | log natural (base \fIe\fP) logarithm |
| 2111 | log10 common (base 10) logarithm |
| 2112 | sqrt square root function (@sqrt x@). |
| 2113 | .R |
| 2114 | .TE |
| 2115 | .DE |
| 2116 | In addition, the following functions accept only |
| 2117 | .B real |
| 2118 | or |
| 2119 | .B "long real" |
| 2120 | arguments: |
| 2121 | .DS |
| 2122 | .TS |
| 2123 | center; |
| 2124 | ll . |
| 2125 | \fBatan\fR @atan(x) = tan sup -1 x@ |
| 2126 | \fBatan2\fR @atan2(x,y) = tan sup -1 x over y@ |
| 2127 | .TE |
| 2128 | .DE |
| 2129 | .NH 3 |
| 2130 | Other Generic Functions |
| 2131 | .PP |
| 2132 | The |
| 2133 | .B sign |
| 2134 | functions takes two arguments of identical type; |
| 2135 | @bold sign (x,y) ~=~ sgn(y) |x|@. |
| 2136 | The |
| 2137 | .B mod |
| 2138 | function yields the remainder of its first argument when divided by its second. |
| 2139 | These functions accept integer and real arguments. |
| 2140 | .NH 1 |
| 2141 | ATAVISMS |
| 2142 | .PP |
| 2143 | Certain facilities are included in the EFL language to ease the conversion of old |
| 2144 | Fortran or Ratfor programs to EFL. |
| 2145 | .NH 2 |
| 2146 | Escape Lines |
| 2147 | .PP |
| 2148 | In order to make use of nonstandard features of the local Fortran compiler, |
| 2149 | it is occasionally necessary to pass a particular line through to the EFL compiler output. |
| 2150 | A line that begins with a percent sign (`\fB%\fR') |
| 2151 | is copied through to the output, with the percent sign removed but no other change. |
| 2152 | Inside of a procedure, each escape line is treated as an executable statement. |
| 2153 | If a sequence of lines constitute a continued Fortran statement, they should be enclosed in braces. |
| 2154 | .NH 2 |
| 2155 | Call Statement |
| 2156 | .PP |
| 2157 | A subroutine call may be preceded by the keyword |
| 2158 | .B call. |
| 2159 | .DS B |
| 2160 | .B |
| 2161 | call joe |
| 2162 | call work(17) |
| 2163 | .R |
| 2164 | .DE |
| 2165 | .NH 2 |
| 2166 | Obsolete Keywords |
| 2167 | .PP |
| 2168 | The following keywords are recognized as synonyms of EFL keywords: |
| 2169 | .TS |
| 2170 | center; |
| 2171 | cc |
| 2172 | ll. |
| 2173 | Fortran EFL |
| 2174 | .sp .3 |
| 2175 | \fBdouble precision long real |
| 2176 | \fBfunction procedure |
| 2177 | \fBsubroutine procedure \fI(untyped)\fR |
| 2178 | .TE |
| 2179 | .NH 2 |
| 2180 | Numeric Labels |
| 2181 | .PP |
| 2182 | Standard statement labels are identifiers. |
| 2183 | A numeric (positive integer constant) label is also permitted; |
| 2184 | the colon is optional following a numeric label. |
| 2185 | .NH 2 |
| 2186 | Implicit Declarations |
| 2187 | .PP |
| 2188 | If a name is used but does not appear in a declaration, |
| 2189 | the EFL compiler gives a warning and assumes a declaration for it. |
| 2190 | If it is used in the context of a procedure invocation, it is assumed to be a procedure name; |
| 2191 | otherwise it is assumed to be a local variable defined at nesting level 1 in the current procedure. |
| 2192 | The assumed type is determined by the first letter of the name. |
| 2193 | The association of letters and types may be given in an |
| 2194 | .B implicit |
| 2195 | statement, with syntax |
| 2196 | .DS C |
| 2197 | \fBimplicit ( \fIletter-list\fB ) \fI type \fR |
| 2198 | .DE |
| 2199 | where a |
| 2200 | .I letter-list |
| 2201 | is a list of individual letters or ranges (pair of letters separated by a minus sign). |
| 2202 | If no |
| 2203 | .B implicit |
| 2204 | statement appears, the following rules are assumed: |
| 2205 | .DS B |
| 2206 | .B |
| 2207 | implicit (a\-h, o\-z) real |
| 2208 | implicit (i\-n) integer |
| 2209 | .R |
| 2210 | .DE |
| 2211 | .NH 2 |
| 2212 | Computed \fBgoto\fR |
| 2213 | .PP |
| 2214 | Fortran contains an indexed multi-way branch; this facility may be used in EFL |
| 2215 | by the computed GOTO: |
| 2216 | .DS C |
| 2217 | \fBgoto ( \fI\*([[ label \*(]] \fB), \fIexpression\fR |
| 2218 | .DE |
| 2219 | The expression must be of type integer and be positive but be no larger than the number of labels in the list. |
| 2220 | Control is passed to the statement marked by the label whose position in the list is equal to the expression. |
| 2221 | .NH 2 |
| 2222 | Go To Statement |
| 2223 | .PP |
| 2224 | In unconditional and computed \fBgoto\fR |
| 2225 | statements, it is permissible to separate the \fBgo\fR and \fBto\fR words, as in |
| 2226 | .DS B |
| 2227 | .B |
| 2228 | go to xyz |
| 2229 | .R |
| 2230 | .DE |
| 2231 | .NH 2 |
| 2232 | Dot Names |
| 2233 | .PP |
| 2234 | Fortran uses a restricted character set, |
| 2235 | and represents certain operators by multi-character sequences. |
| 2236 | There is an option (\fBdots=on\fR; see Section 10.2) which forces the compiler to recognize the forms |
| 2237 | in the second column below: |
| 2238 | .DS |
| 2239 | .B |
| 2240 | .TS |
| 2241 | center; |
| 2242 | ll. |
| 2243 | < .lt. |
| 2244 | <= .le. |
| 2245 | > .gt. |
| 2246 | >= .ge. |
| 2247 | == .eq. |
| 2248 | \*~= .ne. |
| 2249 | & .and. |
| 2250 | | .or. |
| 2251 | && .andand. |
| 2252 | |\|| .oror. |
| 2253 | \*~ .not. |
| 2254 | true .true. |
| 2255 | false .false. |
| 2256 | .TE |
| 2257 | .R |
| 2258 | .DE |
| 2259 | In this mode, no structure element may be named |
| 2260 | .B lt, |
| 2261 | .B le, |
| 2262 | etc. |
| 2263 | The readable forms in the left column are always recognized. |
| 2264 | .NH 2 |
| 2265 | Complex Constants |
| 2266 | .PP |
| 2267 | A complex constant may be written as a parenthesized list of real quantities, such as |
| 2268 | .DS C |
| 2269 | .B |
| 2270 | (1.5, 3.0) |
| 2271 | .R |
| 2272 | .DE |
| 2273 | The preferred notation is by a type coercion, |
| 2274 | .DS C |
| 2275 | .B |
| 2276 | complex(1.5, 3.0) |
| 2277 | .R |
| 2278 | .DE |
| 2279 | .NH 2 |
| 2280 | Function Values |
| 2281 | .PP |
| 2282 | The preferred way to return a value from a function in EFL is the |
| 2283 | @bold return ( value )@ |
| 2284 | construct. |
| 2285 | However, the name of the function acts as a variable to which values may be assigned; |
| 2286 | an ordinary |
| 2287 | @bold return@ |
| 2288 | statement returns the last value assigned to that name as the function value. |
| 2289 | .NH 2 |
| 2290 | Equivalence |
| 2291 | .PP |
| 2292 | A statement of the form |
| 2293 | .EQ C |
| 2294 | bold equivalence ~ v sub 1 ,~ v sub 2 ,~ ...,~ v sub n |
| 2295 | .EN |
| 2296 | declares that each of the @v sub i@ starts at the same memory location. |
| 2297 | Each of the @v sub i@ may be a variable name, array element name, or structure member. |
| 2298 | .NH 2 |
| 2299 | Minimum and Maximum Functions |
| 2300 | .PP |
| 2301 | There are a number of non-generic functions in this category, |
| 2302 | which differ in the required types of the arguments and the type of the return value. |
| 2303 | They may also have variable numbers of arguments, but all the arguments must have the same type. |
| 2304 | .DS |
| 2305 | .TS |
| 2306 | center; |
| 2307 | ccc |
| 2308 | lll . |
| 2309 | Function Argument Type Result Type |
| 2310 | _ |
| 2311 | .B |
| 2312 | amin0 integer real |
| 2313 | amin1 real real |
| 2314 | min0 integer integer |
| 2315 | min1 real integer |
| 2316 | dmin1 long real long real |
| 2317 | |
| 2318 | amax0 integer real |
| 2319 | amax1 real real |
| 2320 | max0 integer integer |
| 2321 | max1 real integer |
| 2322 | dmax1 long real long real |
| 2323 | .R |
| 2324 | .TE |
| 2325 | .DE |
| 2326 | .NH 1 |
| 2327 | COMPILER OPTIONS |
| 2328 | .PP |
| 2329 | A number of options can be used to control the output |
| 2330 | and to tailor it for various compilers and systems. |
| 2331 | The defaults chosen are conservative, but it is sometimes necessary to change the output to match peculiarities of the |
| 2332 | target environment. |
| 2333 | .PP |
| 2334 | Options are set with statements of the form |
| 2335 | .DS C |
| 2336 | \fBoption \fI\*([[ \fIopt \fI\*(]]\fR |
| 2337 | .DE |
| 2338 | where each |
| 2339 | .I opt |
| 2340 | is of one of the forms |
| 2341 | .DS B |
| 2342 | .I |
| 2343 | optionname |
| 2344 | optionname \fB= \fIoptionvalue |
| 2345 | .R |
| 2346 | .DE |
| 2347 | The |
| 2348 | .I optionvalue |
| 2349 | is either a constant (numeric or string) or |
| 2350 | a name associated with that option. |
| 2351 | The two names |
| 2352 | .B yes |
| 2353 | and |
| 2354 | .B no |
| 2355 | apply to a number of options. |
| 2356 | .NH 2 |
| 2357 | Default Options |
| 2358 | .PP |
| 2359 | Each option has a default setting. |
| 2360 | It is possible to change the whole set of defaults to those appropriate |
| 2361 | for a particular environment |
| 2362 | by using the |
| 2363 | .B system |
| 2364 | option. |
| 2365 | At present, the only valid values are |
| 2366 | .B system=unix |
| 2367 | and |
| 2368 | .B system=gcos. |
| 2369 | .NH 2 |
| 2370 | Input Language Options |
| 2371 | .PP |
| 2372 | The |
| 2373 | .B dots |
| 2374 | option determines whether the compiler recognizes |
| 2375 | .B .lt. |
| 2376 | and similar forms. The default setting is |
| 2377 | .B no. |
| 2378 | .NH 2 |
| 2379 | Input/Output Error Handling |
| 2380 | .PP |
| 2381 | The |
| 2382 | .B ioerror |
| 2383 | option can be given three values: |
| 2384 | .B none |
| 2385 | means that none of the I/O statements may be used in expressions, since there is no way to detect errors. |
| 2386 | The implementation of the |
| 2387 | .B ibm |
| 2388 | form uses ERR= and END= clauses. |
| 2389 | The implementation of the |
| 2390 | .B fortran77 |
| 2391 | form uses IOSTAT= clauses. |
| 2392 | .NH 2 |
| 2393 | Continuation Conventions |
| 2394 | .PP |
| 2395 | By default, continued Fortran statements are indicated by a character in column 6 (Standard Fortran). |
| 2396 | The option |
| 2397 | .B "continue=column1" |
| 2398 | puts an ampersand (\fB&\fR) in the first column of the continued lines instead. |
| 2399 | .NH 2 |
| 2400 | Default Formats |
| 2401 | .PP |
| 2402 | If no format is specified for a datum in an |
| 2403 | iolist |
| 2404 | for a |
| 2405 | .B read |
| 2406 | or |
| 2407 | .B write |
| 2408 | statement, a default is provided. |
| 2409 | The default formats can be changed by setting certain options |
| 2410 | .DS |
| 2411 | .TS |
| 2412 | center; |
| 2413 | cc |
| 2414 | ll. |
| 2415 | Option Type |
| 2416 | _ |
| 2417 | \fBiformat\fR integer |
| 2418 | \fBrformat\fR real |
| 2419 | \fBdformat\fR long real |
| 2420 | \fBzformat\fR complex |
| 2421 | \fBzdformat\fR long complex |
| 2422 | \fBlformat\fR logical |
| 2423 | .TE |
| 2424 | .DE |
| 2425 | The associated value must be a Fortran format, such as |
| 2426 | .DS C |
| 2427 | .B |
| 2428 | option rformat=f22.6 |
| 2429 | .R |
| 2430 | .DE |
| 2431 | .NH 2 |
| 2432 | Alignments and Sizes |
| 2433 | .PP |
| 2434 | In order to implement |
| 2435 | .B character |
| 2436 | variables, structures, and the |
| 2437 | .B sizeof |
| 2438 | and |
| 2439 | .B lengthof |
| 2440 | operators, it is necessary to know how much space various Fortran data types require, |
| 2441 | and what boundary alignment properties they demand. |
| 2442 | The relevant options are |
| 2443 | .DS |
| 2444 | .B |
| 2445 | .TS |
| 2446 | center; |
| 2447 | ccc |
| 2448 | lll. |
| 2449 | Fortran Type Size Option Alignment Option |
| 2450 | _ |
| 2451 | integer isize ialign |
| 2452 | real rsize ralign |
| 2453 | long real dsize dalign |
| 2454 | complex zsize zalign |
| 2455 | logical lsize lalign |
| 2456 | .R |
| 2457 | .TE |
| 2458 | .DE |
| 2459 | The sizes are given in terms of an arbitrary unit; |
| 2460 | the alignment is given in the same units. |
| 2461 | The option |
| 2462 | .B charperint |
| 2463 | gives the number of characters per |
| 2464 | .B integer |
| 2465 | variable. |
| 2466 | .NH 2 |
| 2467 | Default Input/Output Units |
| 2468 | .PP |
| 2469 | The options |
| 2470 | .B ftnin |
| 2471 | and |
| 2472 | .B ftnout |
| 2473 | are the numbers of the standard input and output units. |
| 2474 | The default values are |
| 2475 | .B ftnin=5 |
| 2476 | and |
| 2477 | .B ftnout=6. |
| 2478 | .NH 2 |
| 2479 | Miscellaneous Output Control Options |
| 2480 | .PP |
| 2481 | Each Fortran procedure generated by the compiler will be preceded by the value of the |
| 2482 | .B procheader |
| 2483 | option. |
| 2484 | .PP |
| 2485 | No Hollerith strings will be passed as subroutine arguments if |
| 2486 | .B hollincall=no |
| 2487 | is specified. |
| 2488 | .PP |
| 2489 | The Fortran statement numbers normally start at 1 and increase by 1. |
| 2490 | It is possible to change the increment value by using the |
| 2491 | .B deltastno |
| 2492 | option. |
| 2493 | .ta .5i 1i 1.5i 2i 2.5i 3.0i |
| 2494 | .NH 1 |
| 2495 | EXAMPLES |
| 2496 | .PP |
| 2497 | In order to show the flavor or programming in EFL, |
| 2498 | we present a few examples. |
| 2499 | They are short, but show some of the convenience of the language. |
| 2500 | .NH 2 |
| 2501 | File Copying |
| 2502 | .PP |
| 2503 | The following short program copies the standard input to the standard output, |
| 2504 | provided that the input is a formatted file containing |
| 2505 | lines no longer than a hundred characters. |
| 2506 | .DS |
| 2507 | .B |
| 2508 | procedure # main program |
| 2509 | character(100) line |
| 2510 | |
| 2511 | while( read( , line) == 0 ) |
| 2512 | write( , line) |
| 2513 | end |
| 2514 | .R |
| 2515 | .DE |
| 2516 | Since |
| 2517 | .B read |
| 2518 | returns |
| 2519 | zero |
| 2520 | until the end of file (or a read error), |
| 2521 | this program keeps reading and writing until the input is exhausted. |
| 2522 | .NH 2 |
| 2523 | Matrix Multiplication |
| 2524 | .PP |
| 2525 | The following procedure multiplies the |
| 2526 | @m times n@ matrix a |
| 2527 | by the |
| 2528 | @n times p@ matrix b |
| 2529 | to give the @m times p@ matrix c. |
| 2530 | The calculation obeys the formula |
| 2531 | @c sub ij ~=~ sum a sub ik b sub kj@. |
| 2532 | .DS |
| 2533 | .ta .7i 1.4i 2.1i 2.8i |
| 2534 | .B |
| 2535 | procedure matmul(a,b,c, m,n,p) |
| 2536 | integer i, j, k, m, n, p |
| 2537 | long real a(m,n), b(n,p), c(m,p) |
| 2538 | .sp .3 |
| 2539 | do i = 1,m |
| 2540 | do j = 1,p |
| 2541 | { |
| 2542 | c(i,j) = 0 |
| 2543 | do k = 1,n |
| 2544 | c(i,j) += a(i,k) \(** b(k,j) |
| 2545 | } |
| 2546 | end |
| 2547 | .R |
| 2548 | .DE |
| 2549 | .NH 2 |
| 2550 | Searching a Linked List |
| 2551 | .PP |
| 2552 | Assume we have a list of pairs of numbers @(x,y)@. |
| 2553 | The list is stored as a linked list sorted in ascending order of @x@ values. |
| 2554 | The following procedure searches this list for a particular value of @x@ |
| 2555 | and returns the corresponding @y@ value. |
| 2556 | .DS |
| 2557 | .B |
| 2558 | .ta .7i 1.4i 2.1i 2.8i |
| 2559 | define LAST 0 |
| 2560 | define NOTFOUND \-1 |
| 2561 | |
| 2562 | integer procedure val(list, first, x) |
| 2563 | |
| 2564 | # list is an array of structures. |
| 2565 | # Each structure contains a thread index value, an x, and a y value. |
| 2566 | .sp .3 |
| 2567 | struct |
| 2568 | { |
| 2569 | integer nextindex |
| 2570 | integer x, y |
| 2571 | } list(\(**) |
| 2572 | .sp .3 |
| 2573 | integer first, p, arg |
| 2574 | |
| 2575 | for(p = first , p\*~=LAST && list(p).x<=x , p = list(p).nextindex) |
| 2576 | if(list(p).x == x) |
| 2577 | return( list(p).y ) |
| 2578 | |
| 2579 | return(NOTFOUND) |
| 2580 | end |
| 2581 | .R |
| 2582 | .DE |
| 2583 | The search is a single |
| 2584 | .B for |
| 2585 | loop that begins with the head of the list |
| 2586 | and examines items until either the list is exhausted |
| 2587 | (p==LAST) |
| 2588 | or until it is known that the specified value is not on the list |
| 2589 | (list(p).x > x). |
| 2590 | The two tests in the conjunction must |
| 2591 | be performed in the specified order |
| 2592 | to avoid using an invalid subscript in the |
| 2593 | .B list(p) |
| 2594 | reference. |
| 2595 | Therefore, the |
| 2596 | .B && |
| 2597 | operator is used. |
| 2598 | The next element in the chain is found by the iteration statement |
| 2599 | .B "p=list(p).nextindex". |
| 2600 | .NH 2 |
| 2601 | Walking a Tree |
| 2602 | .PP |
| 2603 | As an example of a more complicated problem, let us imagine we have |
| 2604 | an expression tree stored in a common area, |
| 2605 | and that we want to print out an infix form of the tree. |
| 2606 | Each node is either a leaf (containing a numeric value) |
| 2607 | or it is a binary operator, pointing to a left and a right descendant. |
| 2608 | In a recursive language, |
| 2609 | such a tree walk would be implement by the following simple pseudocode: |
| 2610 | .DS |
| 2611 | .I |
| 2612 | if this node is a leaf |
| 2613 | print its value |
| 2614 | otherwise |
| 2615 | print a left parenthesis |
| 2616 | print the left node |
| 2617 | print the operator |
| 2618 | print the right node |
| 2619 | print a right parenthesis |
| 2620 | .R |
| 2621 | .DE |
| 2622 | In a nonrecursive language like EFL, it is necessary to maintain an explicit stack |
| 2623 | to keep track of the current state of the computation. |
| 2624 | The following procedure |
| 2625 | calls a procedure |
| 2626 | .B outch |
| 2627 | to print a single character |
| 2628 | and a procedure |
| 2629 | .B outval |
| 2630 | to print a value. |
| 2631 | .DS |
| 2632 | .ta .7i 1.4i 2.1i 2.8i |
| 2633 | .B |
| 2634 | procedure walk(first) # print out an expression tree |
| 2635 | .sp .5 |
| 2636 | integer first # index of root node |
| 2637 | integer currentnode |
| 2638 | integer stackdepth |
| 2639 | common(nodes) struct |
| 2640 | { |
| 2641 | character(1) op |
| 2642 | integer leftp, rightp |
| 2643 | real val |
| 2644 | } tree(100) # array of structures |
| 2645 | .sp .5 |
| 2646 | struct |
| 2647 | { |
| 2648 | integer nextstate |
| 2649 | integer nodep |
| 2650 | } stackframe(100) |
| 2651 | .sp .5 |
| 2652 | define NODE tree(currentnode) |
| 2653 | define STACK stackframe(stackdepth) |
| 2654 | .sp .5 |
| 2655 | # nextstate values |
| 2656 | define DOWN 1 |
| 2657 | define LEFT 2 |
| 2658 | define RIGHT 3 |
| 2659 | .DE |
| 2660 | .DS |
| 2661 | .B |
| 2662 | # initialize stack with root node |
| 2663 | stackdepth = 1 |
| 2664 | STACK.nextstate = DOWN |
| 2665 | STACK.nodep = first |
| 2666 | .DE |
| 2667 | .DS |
| 2668 | .B |
| 2669 | while( stackdepth > 0 ) |
| 2670 | { |
| 2671 | currentnode = STACK.nodep |
| 2672 | select(STACK.nextstate) |
| 2673 | { |
| 2674 | case DOWN: |
| 2675 | if(NODE.op == " ") # a leaf |
| 2676 | { |
| 2677 | outval( NODE.val ) |
| 2678 | stackdepth \-= 1 |
| 2679 | } |
| 2680 | else { # a binary operator node |
| 2681 | outch( "(" ) |
| 2682 | STACK.nextstate = LEFT |
| 2683 | stackdepth += 1 |
| 2684 | STACK.nextstate = DOWN |
| 2685 | STACK.nodep = NODE.leftp |
| 2686 | } |
| 2687 | .sp .5 |
| 2688 | case LEFT: |
| 2689 | outch( NODE.op ) |
| 2690 | STACK.nextstate = RIGHT |
| 2691 | stackdepth += 1 |
| 2692 | STACK.nextstate = DOWN |
| 2693 | STACK.nodep = NODE.rightp |
| 2694 | .sp .5 |
| 2695 | case RIGHT: |
| 2696 | outch( ")" ) |
| 2697 | stackdepth \-= 1 |
| 2698 | } |
| 2699 | } |
| 2700 | end |
| 2701 | .DE |
| 2702 | .NH 1 |
| 2703 | PORTABILITY |
| 2704 | .PP |
| 2705 | One of the major goals of the EFL language is to make it easy to write portable programs. |
| 2706 | The output of the EFL compiler is intended to be acceptable to any Standard Fortran |
| 2707 | compiler |
| 2708 | (unless the |
| 2709 | .B fortran77 |
| 2710 | option is specified). |
| 2711 | .NH 2 |
| 2712 | Primitives |
| 2713 | .PP |
| 2714 | Certain EFL operations cannot be implemented in portable Fortran, |
| 2715 | so a few machine-dependent procedures must be provided in each environment. |
| 2716 | .NH 3 |
| 2717 | Character String Copying |
| 2718 | .PP |
| 2719 | The subroutine |
| 2720 | .B ef1asc |
| 2721 | is called to copy one character string to another. |
| 2722 | If the target string is shorter than the source, |
| 2723 | the final characters are not copied. |
| 2724 | If the target string is longer, its end is padded with blanks. |
| 2725 | The calling sequence is |
| 2726 | .DS B |
| 2727 | subroutine ef1asc(a, la, b, lb) |
| 2728 | integer a(\(**), la, b(\(**), lb |
| 2729 | .DE |
| 2730 | and it must copy the first |
| 2731 | .B lb |
| 2732 | characters from |
| 2733 | .B b |
| 2734 | to the first |
| 2735 | .B la |
| 2736 | characters of |
| 2737 | .B a. |
| 2738 | .NH 3 |
| 2739 | Character String Comparisons |
| 2740 | .PP |
| 2741 | The function |
| 2742 | .B ef1cmc |
| 2743 | is invoked to determine the order of two character strings. |
| 2744 | The declaration is |
| 2745 | .DS B |
| 2746 | integer function ef1cmc(a, la, b, lb) |
| 2747 | integer a(\(**), la, b(\(**), lb |
| 2748 | .DE |
| 2749 | The function returns a negative value if the string |
| 2750 | .B a |
| 2751 | of length |
| 2752 | .B la |
| 2753 | precedes the string |
| 2754 | .B b |
| 2755 | of length |
| 2756 | .B lb. |
| 2757 | It returns zero if the strings are equal, and a positive value otherwise. |
| 2758 | If the strings are of differing length, the comparison is carried out |
| 2759 | as if the end of the shorter string were padded with blanks. |
| 2760 | .NH 1 |
| 2761 | ACKNOWLEDGMENTS |
| 2762 | .PP |
| 2763 | A. D. Hall originated the EFL language and wrote the first compiler for it; |
| 2764 | he also gave inestimable aid when I took up the project. |
| 2765 | B. W. Kernighan and W. S. Brown made a number of useful suggestions about the language and about this report. |
| 2766 | N. L. Schryer has acted as willing, cheerful, and severe first user |
| 2767 | and helpful critic of each new version and facility. |
| 2768 | J. L. Blue, L. C. Kaufman, and D. D. Warner |
| 2769 | made very useful contributions by making serious use of the compiler, |
| 2770 | and noting and tolerating its misbehaviors. |
| 2771 | .NH 1 |
| 2772 | REFERENCE |
| 2773 | .IP 1. |
| 2774 | B. W. Kernighan, |
| 2775 | ``Ratfor \(em A Preprocessor for a Rational Fortran'', |
| 2776 | Bell Laboratories Computing Science Technical Report #55 |
| 2777 | .bp |
| 2778 | .SH |
| 2779 | APPENDIX A. Relation Between EFL and Ratfor |
| 2780 | .PP |
| 2781 | There are a number of differences between Ratfor and EFL, |
| 2782 | since EFL is a defined language while Ratfor is |
| 2783 | the union of the special control structures and the language accepted by the underlying Fortran compiler. |
| 2784 | Ratfor running over Standard Fortran is almost a subset of EFL. |
| 2785 | Most of the features described in the Atavisms section are present to ease |
| 2786 | the conversion of Ratfor programs to EFL. |
| 2787 | .PP |
| 2788 | There are a few incompatibilities: |
| 2789 | The syntax of the |
| 2790 | .B for |
| 2791 | statement is slightly different in the two languages: |
| 2792 | the three clauses are separated by semicolons in Ratfor, |
| 2793 | but by commas in EFL. |
| 2794 | (The initial and iteration statements may be compound statements in EFL because of this change). |
| 2795 | The input/output syntax is quite different in the two languages, |
| 2796 | and there is no FORMAT statement in EFL. |
| 2797 | There are no ASSIGN or assigned GOTO statements in EFL. |
| 2798 | .PP |
| 2799 | The major linguistic additions are |
| 2800 | character data, |
| 2801 | factored declaration syntax, |
| 2802 | block structure, |
| 2803 | assignment and sequential test operators, |
| 2804 | generic functions, |
| 2805 | and |
| 2806 | data structures. |
| 2807 | EFL permits more general forms for expressions, |
| 2808 | and provides a more uniform syntax. |
| 2809 | (One need not worry about the Fortran/Ratfor restrictions |
| 2810 | on subscript or DO expression forms, for example.) |
| 2811 | .SH |
| 2812 | APPENDIX B. COMPILER |
| 2813 | .SH |
| 2814 | B.1. Current Version |
| 2815 | .PP |
| 2816 | The current version of the EFL compiler is a two-pass translator written in |
| 2817 | portable C. |
| 2818 | It implements all of the features of the language described above except for |
| 2819 | .B "long complex" |
| 2820 | numbers. |
| 2821 | Versions of this compiler run under the |
| 2822 | .SM GCOS |
| 2823 | and |
| 2824 | .UX |
| 2825 | operating systems. |
| 2826 | .SH |
| 2827 | B.2. Diagnostics |
| 2828 | .PP |
| 2829 | The EFL compiler diagnoses all syntax errors. |
| 2830 | It gives the line and file name (if known) on which the error was detected. |
| 2831 | Warnings are given for variables that are used but not explicitly declared. |
| 2832 | .SH |
| 2833 | B.3. Quality of Fortran Produced |
| 2834 | .PP |
| 2835 | The Fortran produced by EFL is quite clean and readable. |
| 2836 | To the extent possible, the variable names that appear in the EFL program are used in the Fortran code. |
| 2837 | The bodies of loops and test constructs are indented. |
| 2838 | Statement numbers are consecutive. |
| 2839 | Few unneeded GOTO and CONTINUE statements are used. |
| 2840 | It is considered a compiler bug if incorrect Fortran is produced |
| 2841 | (except for escaped lines). |
| 2842 | The following is the Fortran procedure produced by the EFL compiler for |
| 2843 | the matrix multiplication example (Section 11.2): |
| 2844 | .DS B |
| 2845 | .B |
| 2846 | \0\0\0\0\0\0subroutine\0matmul(a,\0b,\0c,\0m,\0n,\0p) |
| 2847 | \0\0\0\0\0\0integer\0m,\0n,\0p |
| 2848 | \0\0\0\0\0\0double\0precision\0a(m,\0n),\0b(n,\0p),\0c(m,\0p) |
| 2849 | \0\0\0\0\0\0integer\0i,\0j,\0k |
| 2850 | \0\0\0\0\0\0do\0\03\0i\0=\01,\0m |
| 2851 | \0\0\0\0\0\0\0\0\0do\0\02\0j\0=\01,\0p |
| 2852 | \0\0\0\0\0\0\0\0\0\0\0\0c(i,\0j)\0=\00 |
| 2853 | \0\0\0\0\0\0\0\0\0\0\0\0do\0\01\0k\0=\01,\0n |
| 2854 | \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0c(i,\0j)\0=\0c(i,\0j)+a(i,\0k)*b(k,\0j) |
| 2855 | \0\0\01\0\0\0\0\0\0\0\0\0\0\0continue |
| 2856 | \0\0\02\0\0\0\0\0\0\0\0continue |
| 2857 | \0\0\03\0\0\0\0\0continue |
| 2858 | \0\0\0\0\0\0end |
| 2859 | .R |
| 2860 | .DE |
| 2861 | The following is the procedure for the tree walk (Section 11.4): |
| 2862 | .DS B |
| 2863 | .B |
| 2864 | \0\0\0\0\0\0subroutine\0walk(first) |
| 2865 | \0\0\0\0\0\0integer\0first |
| 2866 | \0\0\0\0\0\0common\0/nodes/\0tree |
| 2867 | \0\0\0\0\0\0integer\0tree(4,\0100) |
| 2868 | \0\0\0\0\0\0real\0tree1(4,\0100) |
| 2869 | \0\0\0\0\0\0integer\0staame(2,\0100),\0stapth,\0curode |
| 2870 | \0\0\0\0\0\0integer\0const1(1) |
| 2871 | \0\0\0\0\0\0equivalence\0(tree(1,1),\0tree1(1,1)) |
| 2872 | \0\0\0\0\0\0data\0const1(1)/4h\0\0\0\0/ |
| 2873 | c\0print\0out\0an\0expression\0tree |
| 2874 | c\0index\0of\0root\0node |
| 2875 | c\0array\0of\0structures |
| 2876 | c\0\0\0nextstate\0values |
| 2877 | c\0\0\0initialize\0stack\0with\0root\0node |
| 2878 | \0\0\0\0\0\0stapth\0=\01 |
| 2879 | \0\0\0\0\0\0staame(1,\0stapth)\0=\01 |
| 2880 | \0\0\0\0\0\0staame(2,\0stapth)\0=\0first |
| 2881 | \0\0\01\0\0if\0(stapth\0.le.\00)\0goto\0\09 |
| 2882 | \0\0\0\0\0\0\0\0\0curode\0=\0staame(2,\0stapth) |
| 2883 | \0\0\0\0\0\0\0\0\0goto\0\07 |
| 2884 | \0\0\02\0\0\0\0\0\0\0\0if\0(tree(1,\0curode)\0.ne.\0const1(1))\0goto\03 |
| 2885 | \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0call\0outval(tree1(4,\0curode)) |
| 2886 | c\0a\0leaf |
| 2887 | \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0stapth\0=\0stapth-1 |
| 2888 | \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0goto\0\04 |
| 2889 | \0\0\03\0\0\0\0\0\0\0\0\0\0\0call\0outch(1h() |
| 2890 | c\0a\0binary\0operator\0node |
| 2891 | \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0staame(1,\0stapth)\0=\02 |
| 2892 | \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0stapth\0=\0stapth+1 |
| 2893 | \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0staame(1,\0stapth)\0=\01 |
| 2894 | \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0staame(2,\0stapth)\0=\0tree(2,\0curode) |
| 2895 | \0\0\04\0\0\0\0\0\0\0\0goto\0\08 |
| 2896 | \0\0\05\0\0\0\0\0\0\0\0call\0outch(tree(1,\0curode)) |
| 2897 | \0\0\0\0\0\0\0\0\0\0\0\0staame(1,\0stapth)\0=\03 |
| 2898 | \0\0\0\0\0\0\0\0\0\0\0\0stapth\0=\0stapth+1 |
| 2899 | \0\0\0\0\0\0\0\0\0\0\0\0staame(1,\0stapth)\0=\01 |
| 2900 | \0\0\0\0\0\0\0\0\0\0\0\0staame(2,\0stapth)\0=\0tree(3,\0curode) |
| 2901 | \0\0\0\0\0\0\0\0\0\0\0\0goto\0\08 |
| 2902 | \0\0\06\0\0\0\0\0\0\0\0call\0outch(1h)) |
| 2903 | \0\0\0\0\0\0\0\0\0\0\0\0stapth\0=\0stapth-1 |
| 2904 | \0\0\0\0\0\0\0\0\0\0\0\0goto\0\08 |
| 2905 | \0\0\07\0\0\0\0\0\0\0\0if\0(staame(1,\0stapth)\0.eq.\03)\0goto\0\06 |
| 2906 | \0\0\0\0\0\0\0\0\0\0\0\0if\0(staame(1,\0stapth)\0.eq.\02)\0goto\0\05 |
| 2907 | \0\0\0\0\0\0\0\0\0\0\0\0if\0(staame(1,\0stapth)\0.eq.\01)\0goto\0\02 |
| 2908 | \0\0\08\0\0\0\0\0continue |
| 2909 | \0\0\0\0\0\0\0\0\0goto\0\01 |
| 2910 | \0\0\09\0\0continue |
| 2911 | \0\0\0\0\0\0end |
| 2912 | .R |
| 2913 | .DE |
| 2914 | .SH |
| 2915 | APPENDIX C. CONSTRAINTS ON THE DESIGN OF THE EFL LANGUAGE |
| 2916 | .PP |
| 2917 | Although Fortran can be used to simulate any finite computation, |
| 2918 | there are realistic limits on the generality of a language that can be |
| 2919 | translated into Fortran. |
| 2920 | The design of EFL was constrained by the implementation strategy. |
| 2921 | Certain of the restrictions are petty (six character external names), |
| 2922 | but others are sweeping (lack of pointer variables). |
| 2923 | The following paragraphs describe the major limitations imposed by Fortran. |
| 2924 | .SH |
| 2925 | C.1. External Names |
| 2926 | .PP |
| 2927 | External names (procedure and COMMON block names) |
| 2928 | must be no longer than six characters in Fortran. |
| 2929 | Further, an external name is global to the entire program. |
| 2930 | Therefore, EFL can support block structure within a procedure, |
| 2931 | but it can have only one level of external name if the |
| 2932 | EFL procedures are to be compilable separately, |
| 2933 | as are Fortran procedures. |
| 2934 | .SH |
| 2935 | C.2. Procedure Interface |
| 2936 | .PP |
| 2937 | The Fortran standards, in effect, permit arguments to be passed between |
| 2938 | Fortran procedures either by reference or by copy-in/copy-out. |
| 2939 | This indeterminacy of specification shows through into EFL. |
| 2940 | A program that depends on the method of argument transmission is |
| 2941 | illegal in either language. |
| 2942 | .PP |
| 2943 | There are no procedure-valued variables in Fortran: a procedure name may |
| 2944 | only be passed as an argument or be invoked; it cannot be stored. |
| 2945 | Fortran (and EFL) would be noticeably simpler if a procedure variable mechanism |
| 2946 | were available. |
| 2947 | .SH |
| 2948 | C.3. Pointers |
| 2949 | .PP |
| 2950 | The most grievous problem with Fortran is its lack of a pointer-like |
| 2951 | data type. |
| 2952 | The implementation of the compiler would have been far easier if certain hard |
| 2953 | cases could have been handled by pointers. |
| 2954 | Further, the language could have been simplified considerably if pointers were |
| 2955 | accessible in Fortran. |
| 2956 | (There are several ways of simulating pointers by using subscripts, |
| 2957 | but they founder on the problems of external variables and initialization.) |
| 2958 | .SH |
| 2959 | C.4. Recursion |
| 2960 | .PP |
| 2961 | Fortran procedures are not recursive, |
| 2962 | so it was not practical to permit EFL procedures to be recursive. |
| 2963 | (Recursive procedures with arguments can be simulated only with great pain.) |
| 2964 | .SH |
| 2965 | C.5. Storage Allocation |
| 2966 | .PP |
| 2967 | The definition of Fortran does not specify the lifetime of variables. |
| 2968 | It would be possible but cumbersome to implement stack or heap |
| 2969 | storage disciplines by using COMMON blocks. |