Re: Yacc/Bison - what semantic actions to take on a parse error

From	James Harris <james.harris.1@gmail.com>
Newsgroups	comp.compilers
Subject	Re: Yacc/Bison - what semantic actions to take on a parse error
Date	2012-05-24 22:49 -0700
Organization	Compilers Central
Message-ID	<12-05-022@comp.compilers> (permalink)
References	<12-05-014@comp.compilers> <12-05-021@comp.compilers>

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On May 24, 8:05 pm, James Harris <james.harri...@gmail.com> wrote:

...

> The issue is that the error production cannot create a meaningful node
> so what actions to replace ACTION are appropriate? Here are some
> options.
>
> * Create an X node with dummy values. That would satisfy the type
> checking.
> * Set $<err_msg>$ = "invalid X node"
> * Braces but no action, i.e. {}
> * No action clause so default to $$ = $1;
> * Some combination of YYERROR; and yyerror();

...

>  http://www.gnu.org/software/bison/manual/html_node/Action-Features.html
>
> So, which option is 'best'? Or should we just ignore a type mismatch
> error?

> [You already know you ran into a syntax error, so I'd think that type
> checking is more likely to produce an error cascade than something
> useful. -John]

It sounds like you might be referring to type checking in the
compiler's later semantic analysis phase. I was asking about the
checking for a type match that the Yacc/Bison build process carries
out.

For example, if we leave the default action $$ = $1 in an error
production the parser creation process might report something like

  $1 of 'X' has no declared type

or, if we set $$ to a dummy

  error: cannot convert dummy_class* to X_class* in assignment

James
[Ah, that, right.  If it were going to try to use the parse tree, I'd
create a dummy node, otherwise { $$ = NULL; }  -John]

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Yacc/Bison - what semantic actions to take on a parse error James Harris <james.harris.1@gmail.com> - 2012-05-23 04:19 -0700
  Re: Yacc/Bison - what semantic actions to take on a parse error James Harris <james.harris.1@gmail.com> - 2012-05-24 12:05 -0700
    Re: Yacc/Bison - what semantic actions to take on a parse error James Harris <james.harris.1@gmail.com> - 2012-05-24 22:49 -0700
      Re: Yacc/Bison - what semantic actions to take on a parse error Chris F Clark <cfc@shell01.TheWorld.com> - 2012-05-30 14:41 -0400

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