Appendix B: Yacc Input Syntax
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
If this identifier is followed by a colon, it is the start of the
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.)
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.
.ta .6i 1.2i 1.8i 2.4i 3i 3.6i
/* grammar for the input to Yacc */
%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 */
spec : defs MARK rules tail
tail : MARK { \fIIn this action, eat up the rest of the file\fR }
| /* empty: the second MARK is optional */
| UNION { \fICopy union definition to output\fR }
| LCURL { \fICopy C code to output file\fR } RCURL
tag : /* empty: union tag is optional */
nmno : IDENTIFIER /* NOTE: literal illegal with %type */
| IDENTIFIER NUMBER /* NOTE: illegal with %type */
rules : C_IDENTIFIER rbody prec
rule : C_IDENTIFIER rbody prec
act : \'{\' { \fICopy action, translate $$, etc.\fR } \'}\'