palindrome.erl

-module(palindrome).
-export([palindrome/1,normalize/1]).
-export([palindrome_test/0,normalize_test/0]).

%% Palindrome %%%

palindrome([]) -> false;
palindrome(S) ->
  Sn = normalize(S),
  palindrome(Sn,lists:reverse(Sn), false).

palindrome([],[],Ac) -> Ac;
palindrome([H1|T1], [H2|T2],_) when H1==H2 ->
  palindrome(T1,T2,true);
palindrome(_,_,_) -> false.

palindrome_test() ->
  false = palindrome(""),
  false = palindrome("    \t\n"),
  true  = palindrome("A"),
  true = palindrome("Madam I\'m Adam"),
  false = palindrome("Not a palindrome!"),
  passed.

%% Normalize strings %%%

% Remove anything not alphanumerical and convert to lowercase
normalize(S) ->
  Sn = re:replace(S, "[[:^alpha:]]", "", [global,{return, list}]),
  string:to_lower(Sn).

normalize_test() ->
  "crazylittlething" = normalize(" ~~ CRaZY LiTTLe THiNG ~~ "),
  "spaceoddity" = normalize(" Space\t Oddity\n    "),
  "dontstopmenow" = normalize("Don\'t Stop Me Now"),
  passed.