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";
}

[download]

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.

[download]

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.

Cheers,
Steffen

In reply to Re^2: Breaking The Rules II by tsee
in thread Breaking The Rules II by Limbic~Region

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.