#!/usr/bin/env perl

# This program reads lambda terms from the standard input and prints
# their simplifications on the standard output.  It's an easy way to
# experiment with the lambda calculus.  You can type lambda as %.
#
# For example, if you type in "(%x x*x)(3)", the program will print "3*3".
# What if you type in "(%x %y x*x + y*y)(3)"?
# How about "(%x %y x*x + y*y)(3)(4+5)"?
#
# Here's a really, really complicated one to try out: 
# You could represent the list "a,b,c" by the term %list list(a)(b)(c).
# The term [%1 %2 %list 2(1(list))] is really a concatenation function
# for such lists.  Try applying it to two of them as follows:
#   [%1 %2 %list 2(1(list))] (%list list(a)(b)(c), %list list(x)(y))

# If you want to type in expressions at the keyboard, try starting up a shell
# in Emacs (by typing "ESC x shell RETURN") and running this program from there.
# This will make it easier to edit your input, and to recall previous inputs
# using ESC p ("previous") and ESC n ("next").

# Please read the top of LambdaTerm.pm for more information about
# what kinds of expressions are allowed and how they are evaluated.

use warnings;
use LambdaTerm 'simplify_safe';
use bytes;

while (<>) {
  chomp;
  my($result) = simplify_safe($_);
  if (defined $result) {
    print "Answer: $result\n";
  } else {
    print STDERR "Error: $@";
  }
}