A Derivation Tool

This is a prototype for a simple tool to show the derivation of your source code from your grammar. A useful script might be:

#!/bin/sh
file=$1
c- -d $file 2>&1 | decoder.pl

#!/usr/bin/perl  -w
# Given the debug out put of a bison parser this
# construct the derivation of a c- file using
# your grammar.
# 
# USAGE:   c- -d yourSource.c- 2>&1 | decoder.pl
#
@stack = ();
while (<>) {
    chomp();
    s/ \(\)//;
    if (/^Shifting/) {
        s/.*token //;
        push @stack, $_;
        print "Shift:  -> ", $_, "\n";
        print "Stack:  ", join(' ', @stack), "\n";
    }
    if (/^Reducing/) {
        s/[^,]*, //;
        /(.*) ?-> (.*)/;
        $from = $1;
        $to = $2;
#            if ($to !~ /^@/) {
        print "Reduce: ", $_, "\n";
        @s = split(/ /, $from);
        $end = $#s+1;
        for ($i=0; $i<$end; $i++) {
            pop @stack;
        }
        push @stack, $to;
        print "Stack:  ", join(' ', @stack), "\n";
#            }
    }
    if (/^Error: popping /) {
        s/^Error: popping \w+ /Pop:    /;
        print $_, " -> \n";
        pop @stack;
        print "Stack:  ", join(' ', @stack), "\n";
    }
    if (/^Error: discarding token /) {
        s/^Error: discarding token /Toss:   /;
        print $_, "\n";
        print "Stack:  ", join(' ', @stack), "\n";
    }
    if (/\*\*/) {
        print "$_\n";
    }
}