parsing make like syntax

[Yuri Shtil]

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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[jtb...@cpan.org]

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