Yacc/Bison, minimize amount by grouping math ops

Question

I am looking at the calc source here http://epaperpress.com/lexandyacc/

I see theses lines in calc.y

| expr \'+\' expr         { $$ = opr(\'+\', 2,          


        

Answer 1

You can do it in 2 ways:

• At lex stage define recognition of operators and provide terminal symbol (in you syntax mathOp) with value of operator '+', '-' ...

• Using mathOp as nonterminal you can return some associated value:

  mathOp : '+' { $$ = '+'; } | '-' { $$ = '-'; } ...

Then usage will look like (pay attention to $2):

| expr mathOp expr         { $$ = opr($2, 2, $1, $3); }

may be you would like to define more complicated mathOp then use %type