[erlang-questions] second try for understanding recursion

[Roelof Wobben]

Hello,

I have studied recursion the last few weeks by using Haskell and I think 
I understand it.

I  did a portion of this exercise :

Write a module boolean.erlthat takes logical expressions and Boolean 
values (represented as the atoms  trueand  false) and returns their 
Boolean result. The functions
you write should include b_not/1, b_and/2, b_or/2, and b_nand/2. You 
should not use
the logical constructs  and,  or, and  not, but instead use pattern 
matching to achieve your
goal.

so far I have this :

-module(boolean).

-export([b_not/1]).

% if a empty string is given , the answer will be a empty string.
b_not('') ->
   '';

% is false is given, the answer will be true.
b_not(false) ->
   true;

% is true is given, the answer will be false
b_not(true) ->
   false.

Is this a good try or can I change anything ?

Roelof