0

I want to ask you a question about Flex, the program for parsing code. Supposing I have an instruction like this one, in the rules part:

"=" BEGIN(attribution);

<attribution>{var_name} { fprintf(yyout, "="); ECHO; }

<attribution>";" BEGIN(INITIAL);

{var_name} is a regular expression that matches a variable's name, and all I want to do is to copy at the output all the attribution instructions, such as a = 3; or b = a;

My rule though cannot write with fprintf the left member of the attribution, but only = 3; or =a;

One solution for that might be that, after I make the match "=" and I am in the attribution state, to go 2 positions back as to get the left operand as well. How can I do that in Flex?

Jonathan Leffler
  • 730,956
  • 141
  • 904
  • 1,278
shkk
  • 1
  • 1

1 Answers1

1

Why are you using flex for syntactical analysis?

What you are doing sounds like a bison stuff not a flex job. You'll be able to store previous token.

If you still want to use flex, you can use the / pattern. Using this may lead to inefficiencies and the lexer can be bogus; it depends of the whole rule set.

{var_name}/"=" { ECHO; BEGIN(attribution); }

See the flex manual.

rici
  • 234,347
  • 28
  • 237
  • 341
VGE
  • 4,171
  • 18
  • 17