Re: parsing make like syntax

I've assumed that you have your value to be substituted in a scalar
variable, that substitutions allowed to introduce new variable
references (   $($(foo)) with foo="$(bar) => $($(bar)) which would then
substitute bar)

I've also assumed that variable names can only contain characters
matching \w.  This means that the innermost substitutions (the innermost
ones) should match m/$\(\w+\)/.

Something like this should work:

    my %subst = ( foo => '$(bar)',
                  bar => 'baz',
                  abcbazdef => 'HELLO',
              );
    my $val = '$(abc$(foo)def)';

    while ($val =~ s/\$\((\w+)\)/$subst{$1}/e) {
        print "VAL $val\n";
    }

    print "$val\n";

I've left out any error checking for undefined values in %subst and the
like.

Using Parse::RecDescent to do this directly would require that you
define a rule something like the following, with $skip probably set to '':

    varvalue: '$(' /\w+/ ')'
    | '$(' /MATCHALLOWEDLITERAL/ substitution /MATCHALLOWEDLITERAL/ ')'
    | /MATCHALLOWEDLITERAL/

The downside of this is that you probably won't be able to easily handle
all cases of recursive substitutions as shown above.  You may be able to
modify $text in the actions for the first two rules above, and make it
work. But I'm assuming you've already got a rule that contains 
/$RE{balanced}{-parens=>'()'}/, and providing a modified version of the
example action above probably gets you where you want to go.

Jeremy

On 1/11/2012 3:52 PM, Yuri Shtil wrote:
> Hi,
>
> I need to parse make variable reference like syntax:
>
> $($(foo))
>
> $(foo) should be detected first, replaced (let's say with bar) and resultant string $(bar) should be parsed the same way.
> There can be any number of nested references like
>
> $(abc$(foo)def)
>
> Any suggestions how to define rules for this?
>
> I used Regexp::Common to detect balanced parenthesis.
>
>
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• parsing make like syntax by Yuri Shtil
• Re: parsing make like syntax by jtbraun