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Re: Breaking The Rules II

by tsee (Curate)
on Jul 02, 2007 at 15:16 UTC ( #624473=note: print w/replies, xml ) Need Help??

in reply to Breaking The Rules II

Quite interesting!

On a side note: When I wrote Math::Symbolic::Parser(::Yapp), I stumbled upon a similar essay at . The author focuses more on the performance aspects of the available parsers or rather parser generators, but he also talks about the amount of work required to get going.


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Re^2: Breaking The Rules II
by tsee (Curate) on Jul 05, 2007 at 09:55 UTC

    I forgot to mention how you'd actually use that specific "wheel" to evaluate expressions. I know it's not the point of this meditation to just use the existing tools, but comparison might still be sensible.

    #!/usr/bin/perl use strict; use warnings; use Math::Symbolic; my $parser = Math::Symbolic::Parser->new(); while (1) { print "\n> "; my $line = <STDIN>; my $tree = $parser->parse($line); print("Parse error.\n"), next if not defined $tree; print "Entered: $tree\n"; my $result = $tree->value(); print("Evaluation error.\n"), next if not defined $result; print "Result: $result\n"; }

    The output would look like this:

    > 3*4.2e3+5^(3.1+2) Entered: (3 * 4.2e3) + (5 ^ (3.1 + 2)) Result: 16270.6841971501 > a*b+c Entered: (a * b) + c Evaluation error.

    That last bit shows that the parser is actually intended to be used with variables, too. So it's not a parse error but an evaluation error.

    Switching to using the YAPP based parser is rather straightforward, too. Just add "implementation => 'Yapp'" to the call to the constructor.


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