Factorial in Erlang

Welcome to the Factorial in Erlang page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

-module(factorial).
-export([main/1]).

usage() ->
    io:format("Usage: please input a non-negative integer~n"),
    halt().

convert_to_integer(Str) ->
    Result = catch string:to_integer(string:strip(Str)),
    case Result of
        {Int, Rest} when Rest == "" ->
            {ok, Int};
        _ ->
            {error, 0}
    end.

main(Args) ->
    if
        length(Args) < 1 ->
            usage();
        true ->
            ok
    end,

    StrValue = lists:nth(1, Args),
    Value = case convert_to_integer(StrValue) of
        {ok, Int} ->
            Int;
        _ ->
            usage()
    end,

    if
        Value < 0 ->
            usage();
        true ->
            ok
    end,

    FValue = factorial(Value),
    io:format("~w~n", [FValue]).

%%--------------------------------------------------------------------
%% Recursively multiply N times N-1 until N <= 1
%%--------------------------------------------------------------------
factorial(0) ->
    1;
factorial(N) ->
    N * factorial(N-1).

Factorial in Erlang was written by:

• Mark Magahis
• rzuckerm

If you see anything you'd like to change or update, please consider contributing.

How to Implement the Solution

No 'How to Implement the Solution' section available. Please consider contributing.

How to Run the Solution

No 'How to Run the Solution' section available. Please consider contributing.