#!/usr/local/bin/perl
# -*- perl -*-

$file = $ARGV[0];
$input = $ARGV[1];

# input Turing machine
open(TM, $file);
while ($line = <TM>) {
    ($st, $sym, $st0, $sym0, $dir) = split(/\s+/,$line);
    $nextst{$st,$sym} = $st0;
    $nextsym{$st,$sym} = $sym0;
    $nextdir{$st,$sym} = $dir;
}

# initialize Turing machine
$tape[0] = "_";
$tape[1] = "_";
foreach $i (0 .. length($input)-1) {
    $tape[$i+2] = substr($input,$i,1);
}
push(@tape,"_");
push(@tape,"_");
$st = "q0";
$pos = 2;
$sym = $tape[2];
$offset = 8;
while (1) {

    # print configuration

    # print the state
    foreach $i (1 .. $offset + $pos) {print " ";}
    print "$st\n";
    foreach $i (1 .. $offset + $pos) {print " ";}
    print "|\n";
    foreach $i (1 .. $offset) {print " ";}
    foreach $i (0 .. $#tape) {print $tape[$i];}
    print "\n";

    # wait for user input

    if (<STDIN>) { };
    
    # perform transition
    ($st, $sym, $dir) =
	($nextst{$st,$sym}, $nextsym{$st,$sym}, $nextdir{$st,$sym});
    last unless defined($dir);
    $tape[$pos] = $sym;
    if ($dir eq "L" || $dir eq "l") {
	$pos--;
	if ($pos < 0) {
	    $pos = 0;
	    $offset--;
	    unshift(@tape,"_");
	}
    }
    elsif ($dir eq "R" || $dir eq "r") {
	$pos++;
	if ($pos > $#tape) {push(@tape,"_");}
    }
    $sym = $tape[$pos];
}