bsb:

OK ... I've toyed around with the code and did a version with the extra parenthesis removal. Here ya go:

#!/usr/bin/perl -w
use strict;
use warnings;

my @stack = ();

sub binop {
        my $op = shift;
        my $prec = shift;

        my $lh = pop @stack;
        my ($lhop, $lhprec) = ($$lh[0], $$lh[1]);

        my $rh = pop @stack;
        my ($rhop, $rhprec) = ($$rh[0], $$rh[1]);

        # Wrap operand(s) with lower precedence
        $lhop = '(' . $lhop . ')' if $prec > $lhprec;
        $rhop = '(' . $rhop . ')' if $prec > $rhprec;

        push @stack, [ $lhop . $op . $rhop, $prec ];
}

while (<DATA>) {
        chomp;

        print "TOS='" . (@stack ? $stack[$#stack][0] : '-nil-') . "' "
        .       "stmt = '" . $_ . "'\n";

        my ($operator, $operand) = split;
        if ($operator eq 'push') {
                # A constant is atomic, so it has high precedence so
                # we don't wrap it
                push @stack, [$operand, 999];
        }
        elsif ($operator eq 'print') {
                my $op = pop @stack;
                my ($operand, $prec) = ($$op[0], $$op[1]);
                print "out: '" . $operand . "'\n";
        }
        elsif ($operator eq 'add') {
                binop '+', 1;
        }
        elsif ($operator eq 'mul') {
                binop '*', 2;
        }
}
__DATA__
push 3
push 5
add
push 7
push 9
add
mul
print

[download]
Which gives us: 
root@swill ~/PerlMonks
$ ./stack_to_infix2.pl
TOS='-nil-' stmt = 'push 3'
TOS='3' stmt = 'push 5'
TOS='5' stmt = 'add'
TOS='5+3' stmt = 'push 7'
TOS='7' stmt = 'push 9'
TOS='9' stmt = 'add'
TOS='9+7' stmt = 'mul'
TOS='(9+7)*(5+3)' stmt = 'print'
out: '(9+7)*(5+3)'

root@swill ~/PerlMonks
$

[download]
--roboticus

P.S. I don't like my code for getting arguments off the stack, but all my attempts at simplifying it failed miserably. I'm sure it's something simple, but I haven't figured it out. What's a better way to do the following? (Or is my problem a bit earlier and I'm pushing the wrong thing on the stack?)

    my $op = pop @stack;
    my ($operand, $prec) = ($$op[0], $$op[1]);

[download]

In reply to Re: Convert stack-based code to "conventional" (was Re: Graphing SQLite's VDBE) by roboticus
in thread Graphing SQLite's VDBE by bsb

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.