CODEWITHSUNDEEP
parsingtokenbisonyaccflex-lexer
xis
xis

Reputation: 24840

Access two or more tokens in one line using Bison

I am using bison to implement a simple parser. And one line of the syntax looks like:

prefix_definition : PREFIX IDENTIFIER IDENTIFIER ABBR IDENTIFIER ';'

I am unsure how to access the 1st, 2nd and 3rd IDENTIFIER separately. My flex file reads the IDENTIFIER like this:

IDENTIFIER_REGEX (_|[A_Za-z])(_|[0-9A-Za-z])*

{IDENTIFIER_REGEX}     { yylval.identifier=strdup(yytext); return IDENTIFIER; }

I could not use simply yylval.identifier. I tried $2.identifier or so but it simply does not work(and it is not supposed to be work anyway). Is there any way of solving this problem?

I am considering to use a FIFO queue if the bison/flex does not support such access. Is this a good solution?

Upvotes: 1

Views: 405

Answers (1)

Ismail Badawi
Ismail Badawi

Reputation: 37167

You can specify the type of a token while declaring it (in the bison file) the same way you would for nonterminals (where you'd use %type) like so:

%token <identifier> IDENTIFIER

(where identifier is one of the fields declared in the %union). Then $2, $3 and so on will point to the right thing, without needing to go through yylval (i.e. they will be char *s in your case).

Upvotes: 2

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