+.th BAS I 1/15/73
+.sh NAME
+bas \*- basic
+.sh SYNOPSIS
+.bd bas
+[ file ]
+.sh DESCRIPTION
+.it Bas
+is a dialect of Basic.
+If a file argument is provided,
+the file is used for input before the console
+is read.
+.it Bas
+accepts lines of the form:
+.s3
+ statement
+ integer statement
+.s3
+Integer numbered statements
+(known as internal statements)
+are stored for later execution.
+They are stored in sorted ascending order.
+Non-numbered statements are immediately executed.
+The result of an immediate expression statement
+(that does not have `=' as its highest operator) is printed.
+.s3
+Statements have the following syntax:
+.s3
+.lp +5 5
+expression
+.br
+The expression is executed for its side
+effects (assignment or function call)
+or for printing as described above.
+.s3
+.lp +5 5
+.bd done
+.br
+Return to system level.
+.s3
+.lp +5 5
+.bd draw
+expression expression expression
+.br
+A line is drawn on the Tektronix 611 display
+`/dev/vt0'
+from
+the current display position
+to the XY co-ordinates specified by the
+first two expressions.
+The scale is zero to one in both X and Y directions.
+If the third expression
+is zero, the line is invisible.
+The current display position is set to the end point.
+.s3
+.lp +5 5
+.bd display
+list
+.br
+The list of expressions and strings is
+concatenated and displayed (i.e. printed) on the 611 starting
+at the current display position.
+The current display position is not changed.
+.s3
+.lp +5 5
+.bd erase
+.br
+The 611 screen is erased.
+.s3
+.lp +5 5
+.bd for
+name
+.bd =
+expression expression statement
+.br
+.lp +5 5
+.bd for
+name
+.bd =
+expression expression
+.br
+.li
+...
+.lp +5 5
+.bd next
+.br
+The
+.it for
+statement
+repetitively executes a
+statement (first form)
+or a group of statements (second form)
+under control of a named variable.
+The variable takes on the value of
+the first expression,
+then is incremented by one on each loop,
+not to exceed the value of
+the second expression.
+.s3
+.lp +5 5
+.bd goto
+expression
+.br
+The expression is evaluated, truncated to an integer
+and execution goes to the corresponding integer numbered statment.
+If executed from immediate mode,
+the internal statements are compiled first.
+.s3
+.lp +5 5
+.bd if
+expression statement
+.br
+The statement is executed if the expression evaluates
+to non-zero.
+.s3
+.lp +5 5
+.bd list
+[expression [expression]]
+.br
+.br list
+is used to print out the stored internal statements.
+If no arguments are given, all internal statements are printed.
+If one argument is given, only that
+internal statement is listed.
+If two arguments are given, all internal statements
+inclusively between the arguments are printed.
+.s3
+.lp +5 5
+.bd print
+list
+.br
+The list of expressions and strings are concatenated and
+printed.
+(A string is delimited by " characters.)
+.s3
+.lp +5 5
+.bd return
+[expression]
+.br
+The expression is evaluated and the result is passed
+back as the value of a function call.
+If no expression is given, zero is returned.
+.s3
+.lp +5 5
+.bd run
+.br
+The internal statements are compiled.
+The symbol table is re-initialized.
+The random number generator is reset.
+Control is passed to the lowest numbered internal
+statement.
+.s3
+.i0
+Expressions have the following syntax:
+.s3
+.lp +5 5
+name
+.br
+A name is used to specify a variable.
+Names are composed of a letter
+followed by letters and digits.
+The first four characters of a name are significant.
+.s3
+.lp +5 5
+number
+.br
+A number is used to represent a constant value.
+A number is written in Fortran style,
+and contains digits, an optional decimal point,
+and possibly a scale factor consisting
+of an \fBe\fR followed by a possibly signed exponent.
+.s3
+.lp +5 5
+.bd (
+expression
+.bd )
+.br
+Parentheses are used to alter normal order of evaluation.
+.s3
+.lp +5 5
+expression operator expression
+.br
+Common functions of two arguments are abbreviated
+by the two arguments separated by an operator denoting the function.
+A complete list of operators is given below.
+.s3
+.lp +5 5
+expression
+.bd (
+[expression [
+.bd ,
+expression] ... ]
+.bd )
+.br
+Functions of an arbitrary number of arguments
+can be called by an expression followed by the arguments
+in parentheses separated by commas.
+The expression evaluates to the
+line number of the entry of the function in the
+internally stored statements.
+This causes the internal statements to be compiled.
+If the expression evaluates negative,
+a builtin function is called.
+The list of builtin functions appears below.
+.s3
+.lp +5 5
+name
+.bd [
+expression
+[
+.bd ,
+expression
+] ...
+.bd ]
+.br
+Each expression is truncated to an integer
+and used as a specifier for the name.
+The result is syntactically identical to a name.
+.bd a[1,2]
+is the same as
+.bd a[1][2].
+The truncated expressions are restricted to
+values between 0 and 32767.
+.s3
+.i0
+The following is the list of operators:
+.s3
+.lp +5 5
+=
+.br
+=
+is the assignment operator.
+The left operand must be a name or an array element.
+The result is the right operand.
+Assignment binds right to left,
+all other operators bind left to right.
+.s3
+.lp +5 5
+& \*v
+.br
+&
+(logical and)
+has result zero if either of its arguments are zero.
+It has result one if both its arguments are non-zero.
+\*v
+(logical or)
+has result zero if both of its arguments are zero.
+It has result one if either of its arguments are non-zero.
+.s3
+.lp +5 5
+< <= > >= == <>
+.br
+The relational operators
+(< less than, <= less than or equal,
+> greater than,
+>= greater than or equal,
+== equal to,
+<> not equal to)
+return one if their arguments are in the specified
+relation.
+They return zero otherwise.
+Relational operators at the same level extend as follows:
+a>b>c is the same as a>b&b>c.
+.s3
+.lp +5 5
++ \*-
+.br
+Add and subtract.
+.s3
+.lp +5 5
+* /
+.br
+Multiply and divide.
+.s3
+.lp +5 5
+^
+.br
+Exponentiation.
+.s3
+.i0
+The following is a list of builtin functions:
+.s3
+.lp +5 5
+.bd arg(i)
+.br
+is the value of the
+\fIi\fR|-th
+actual parameter on the current level
+of function call.
+.s3
+.lp +5 5
+.bd exp(x)
+.br
+is the exponential function of \fIx\fR.
+.s3
+.lp +5 5
+.bd log(x)
+.br
+is the natural logarithm of \fIx\fR.
+.s3
+.lp +5 5
+.bd sin(x)
+.br
+is the sine of \fIx\fR (radians).
+.s3
+.lp +5 5
+.bd cos(x)
+.br
+is the cosine of \fIx\fR (radians).
+.s3
+.lp +5 5
+.bd atn(x)
+.br
+is the arctangent of \fIx\fR . its value
+is between \*-\(*p/2 and \(*p/2.
+.s3
+.lp +5 5
+.bd "rnd( )"
+.br
+is a uniformly distributed random
+number between zero and one.
+.s3
+.lp +5 5
+.bd "expr( )"
+.br
+is the only form of program input.
+A line is read from the input and
+evaluated as an expression.
+The resultant value is returned.
+.s3
+.lp +5 5
+.bd int(x)
+.br
+returns \fIx\fR truncated to an integer.
+.i0
+.sh FILES
+.dt
+/tmp/btm? temporary
+.sh DIAGNOSTICS
+Syntax
+errors cause the incorrect line to be typed
+with an underscore where the parse failed.
+All other diagnostics are self explanatory.
+.sh BUGS
+Has been known to give core images.
+Needs a way to
+.it list
+a program onto a file.
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