Re^2: To make the Model WORK

25-year programmer showing graying roots. :) Real returned values might be '0', as well. That would fail.

I'm fortunate that, the way I've built this, now all I need to do is to 'flatten' the @item from IFTHENELSE into a one-dimensional array and then iterate. The first non-NIL result found will be returned, and I don't care which elsif or else clause gave it to me. Thanks to you and blokhead both, I see light illuminating repeated subrules. :D

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Re^3: To make the Model WORK by ikegami (Patriarch) on Jul 13, 2005 at 16:34 UTC
Real returned values might be '0', as well. That would fail. Nope. `'0'` will not fail a production. Only `undef`. I stand corrected: use Parse::RecDescent; my $parser; $parser = Parse::RecDescent->new(q` test: { $return = 1 } `); print($parser->test('') ? 'ok' : 'fail', "\n"); # ok $parser = Parse::RecDescent->new(q` test: { $return = 0 } `); print($parser->test('') ? 'ok' : 'fail', "\n"); # fail $parser = Parse::RecDescent->new(q` test: { $return = '0' } `); print($parser->test('') ? 'ok' : 'fail', "\n"); # fail $parser = Parse::RecDescent->new(q` test: { $return = undef } `); print($parser->test('') ? 'ok' : 'fail', "\n"); # fail $parser = Parse::RecDescent->new(q` test: /\d+/ `); print($parser->test('1') ? 'ok' : 'fail', "\n"); # ok print($parser->test('0') ? 'ok' : 'fail', "\n"); # fail [download] I never got into that situation, because I'd be returning `[ ident => ident ]` or `[ literal => literal ]` or `[ '*' => expr, expr ]` or `[ '/' => expr, expr ]` or ...	[reply] [d/l] [select]

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Re^3: To make the Model WORK
by ikegami (Patriarch) on Jul 13, 2005 at 16:34 UTC

Real returned values might be '0', as well. That would fail.

Nope. '0' will not fail a production. Only undef.

I stand corrected:

use Parse::RecDescent;

my $parser;

$parser = Parse::RecDescent->new(q` test: { $return = 1 } `);
print($parser->test('') ? 'ok' : 'fail', "\n");  # ok

$parser = Parse::RecDescent->new(q` test: { $return = 0 } `);
print($parser->test('') ? 'ok' : 'fail', "\n");  # fail

$parser = Parse::RecDescent->new(q` test: { $return = '0' } `);
print($parser->test('') ? 'ok' : 'fail', "\n");  # fail

$parser = Parse::RecDescent->new(q` test: { $return = undef } `);
print($parser->test('') ? 'ok' : 'fail', "\n");  # fail

$parser = Parse::RecDescent->new(q` test: /\d+/ `);
print($parser->test('1') ? 'ok' : 'fail', "\n");  # ok
print($parser->test('0') ? 'ok' : 'fail', "\n");  # fail
[download]

I never got into that situation, because I'd be returning
[ ident => ident ]
or
[ literal => literal ]
or
[ '*' => expr, expr ]
or
[ '/' => expr, expr ]
or
...

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