Fibonacci in Erlang, commandline interface

fib.erl

#! /bin/env escript

% NAME
%	fib.erl		-- Erlang exercise with Fibonacci numbers
%
% SYNOPSIS
%	fib  {from-integer}  [{to-integer}]
%
% INSTALL
%	ln -s fib.erl fib
%
% DESCRIPTION
%	FutureLean course "Functional Programming in Erlang".
%	Lesson 1.19 (part of)
%		Recursion Examples
%			Fibonacci Numbers.
%
%	Exercise extended a little with:
%		1) use of "escript" from the commandline,
%		2) generation and display of Fib sequence from N to M,
%		3) generation of Fib sequence list using seq and map.
%
% STEP BY STEP EVALUATION
%	fib(4) = fib(2)            + fib(3)
%	       = (fib(0) + fib(1)) + (fib(1) + fib(2))
%	       = (0 + 1)           + (1      + (fib(0) + fib(1)))
%	       = 1                 + (1      + (0      + 1))
%	       = 1                 + (1      + 1)
%	       = 1                 + 2
%	       = 3
%
% TODO
%	Validity of numeric commandline arguments is not yet checked.

-module(fib).
-export([fib/1, fibShow/1, fibShow/2, fibList/2]).

% A simple term generator function for the Fibonacci Sequence..
% Generates the Nth term of the Fibonacci sequence starting from 0.
fib(0) ->
	0;
fib(1) ->
	1;
fib(N) ->
	fib(N-2) + fib(N-1).

fibShow(N) ->
	io:format("fib(~p) = ~p~n", [N, fib(N)]).

fibShow(N,N) ->
	fibShow(N);
fibShow(N,M) when N =< M ->
	fibShow(N,M-1),
	fibShow(M,M);
fibShow(N,M) ->
	io:format("fib:  ERROR: to-integer ~p is smaller than from-integer ~p~n", [M,N]),
	halt(2).

fibList(N,M) when N =< M ->
	lists:map(fib/1, lists:seq(N,M)).

main() ->
	io:format("Usage:  fib  {from-integer}  [{to-integer}]~n"),
	halt(1).

main([]) ->
	main();

main([NumericString]) ->
	N = list_to_integer(NumericString),
	fibShow(N);

main([FromNumber, ToNumber]) ->
	N = list_to_integer(FromNumber),
	M = list_to_integer(ToNumber),
	fibShow(N,M);

main([_,_,_|_]) ->
        io:format("Too many arguments.~n"),
        main().

Example usage from commandline:

$ ./fib
Usage: fib {from-integer} [{to-integer}]
$ ./fib 0 9
fib(0) = 0
fib(1) = 1
fib(2) = 1
fib(3) = 2
fib(4) = 3
fib(5) = 5
fib(6) = 8
fib(7) = 13
fib(8) = 21
fib(9) = 34