Erlang: commandline interface to factorial using escript

fact.erl

#! /bin/env escript

%% Simplest use of Erlang's escript and commandline arguments
%% for an interface to the tail-recursive factorial function.

-module(fact).

fact(N) ->
	fact(N, 1).

fact(N,Product) when N =< 1 ->
	Product;
fact(N,Product) ->
	fact(N-1, Product*N).

main([]) ->
	io:format("Usage:  fact  {integer}~n"),
	halt(1);
main([NumericString|_]) ->
	N = list_to_integer(NumericString),
	io:format("fact(~p) = ~p~n", [N, fact(N)]).

thanks for sharing, very useful to see it applied like this!