-Suppose that the Yacc specification is on a file called
-yfile.
-If the actions are in C, Yacc is invoked by
-.DS
-yacc yfile
-.DE
-The output appears on file y.tab.c
-To compile the parser and load it with
-the Yacc library, use the command
-.DS
-cc y.tab.c \-ly
-.DE
-If Yacc is invoked with the option \-v:
-.DS
-yacc \-v yfile
-.DE
-a verbose description of the parser is produced on file y.output.
-The C user should consult section
-6C for more information about the run time environment.
-.PP
-If the actions are in Ratfor,
-the user should invoke Yacc with the option \-r:
-.DS
-yacc \-r yfile
-.DE
-The Ratfor output appears on file y.tab.r
-It may be compiled by
-.DS
-rc \-2 y.tab.r
-.DE
-Note that when Yacc is used to produce Ratfor
-programs, there is no need to load these programs with any library.
-.PP
-If the \-v action is also invoked:
-.DS
-yacc \-rv yfile
-.DE
-a verbose description of the parser is produced on file y.output.
-The Ratfor user should consult section 6R for more information about
-the run time environment.
+This Appendix has a description of the Yacc input syntax, as a Yacc specification.
+Context dependencies, etc., are not considered.
+Ironically, the Yacc input specification language
+is most naturally specified as an LR(2) grammar; the sticky
+part comes when an identifier is seen in a rule, immediately
+following an action.
+If this identifier is followed by a colon, it is the start of the
+next rule; otherwise
+it is a continuation of the current rule, which just happens to have
+an action embedded in it.
+As implemented, the lexical analyzer looks
+ahead after seeing an identifier, and
+decide whether the next token (skipping blanks, newlines, comments, etc.)
+is a colon.
+If so, it returns the token C_IDENTIFIER.
+Otherwise, it returns IDENTIFIER.
+Literals (quoted strings) are also returned as IDENTIFIERS,
+but never as part of C_IDENTIFIERs.
+.sp
+.nf
+.ta .6i 1.2i 1.8i 2.4i 3i 3.6i
+
+ /* grammar for the input to Yacc */
+
+ /* basic entities */
+%token IDENTIFIER /* includes identifiers and literals */
+%token C_IDENTIFIER /* identifier (but not literal) followed by colon */
+%token NUMBER /* [0-9]+ */
+
+ /* reserved words: %type => TYPE, %left => LEFT, etc. */
+
+%token LEFT RIGHT NONASSOC TOKEN PREC TYPE START UNION
+
+%token MARK /* the %% mark */
+%token LCURL /* the %{ mark */
+%token RCURL /* the %} mark */
+
+ /* ascii character literals stand for themselves */
+
+%start spec
+
+%%
+
+spec : defs MARK rules tail
+ ;
+
+tail : MARK { \fIIn this action, eat up the rest of the file\fR }
+ | /* empty: the second MARK is optional */
+ ;
+
+defs : /* empty */
+ | defs def
+ ;
+
+def : START IDENTIFIER
+ | UNION { \fICopy union definition to output\fR }
+ | LCURL { \fICopy C code to output file\fR } RCURL
+ | ndefs rword tag nlist
+ ;
+
+rword : TOKEN
+ | LEFT
+ | RIGHT
+ | NONASSOC
+ | TYPE
+ ;
+
+tag : /* empty: union tag is optional */
+ | \'<\' IDENTIFIER \'>\'
+ ;
+
+nlist : nmno
+ | nlist nmno
+ | nlist \',\' nmno
+ ;
+
+nmno : IDENTIFIER /* NOTE: literal illegal with %type */
+ | IDENTIFIER NUMBER /* NOTE: illegal with %type */
+ ;
+
+ /* rules section */
+
+rules : C_IDENTIFIER rbody prec
+ | rules rule
+ ;
+
+rule : C_IDENTIFIER rbody prec
+ | '|' rbody prec
+ ;
+
+rbody : /* empty */
+ | rbody IDENTIFIER
+ | rbody act
+ ;
+
+act : \'{\' { \fICopy action, translate $$, etc.\fR } \'}\'
+ ;
+
+prec : /* empty */
+ | PREC IDENTIFIER
+ | PREC IDENTIFIER act
+ | prec \';\'
+ ;
+.fi
+.bp
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