Extension to Erlang

[Joe Armstrong]

Hi Guys,
 
  I'd lkie to posproe an einotsexn to the fatrnoimig civoentonns uesd
in io:foamrt. I'd lkie to see a ~w wichh wpars the opuutt text.

  I have wtteirn warp.erl wihch waprs a flie (apdepned) - it should be
pttery esay to ilnudce tihs itno the sraatdnd laiirebrs.

  This  ieda is  besad  on  smoe ctintug  edge  reecrash at  Cgramidbe
Uientvsiry which has shwon that it deosn't rellay mttear how wrods are
selpt as long as the frist and lsat lrttees are cecorrt.

  Cehers

  /Joe

---- cut ----

-module(warp).
-import(lists, [map/2, reverse/1]).

-export([file/1, word/1]).

file(F) ->
    {ok, B} = file:read_file(F),
    L = binary_to_list(B),
    L1 = tokenise(L, []),
    Lines = map(fun warp_line/1, L1),
    file:write_file(F ++ ".warp", Lines).

is_alpha(X) when X >= $a, X =< $z -> true;
is_alpha(X) when X >= $A, X =< $Z -> true;
is_alpha(X) -> false.
	    
tokenise(All = [H|T], L) ->
    case is_alpha(H) of
	true ->
	    {Word, Rest} = collect_while(fun is_alpha/1, All),
	    tokenise(Rest, [{word,Word}|L]);
	false ->
	    tokenise(T, [H|L])
    end;
tokenise([], L) ->
    reverse(L).

collect_while(Pred, L) ->
    collect_while(Pred, L, []).

collect_while(pred, [], L) ->
    {[], reverse(L)};
collect_while(Pred, All = [H|T], L) ->
    case Pred(H) of
	true ->
	    collect_while(Pred, T, [H|L]);
	false ->
	    {reverse(L), All}
    end.

warp_line({word,L}) -> word(L);
warp_line(X) -> X.

word([X]) ->
    X;
word([H|T]) ->			
    [Last|R] = reverse(T),
    [H|reverse([Last|warp_word(R, [])])].

warp_word([], L) ->
    L;
warp_word(L1, L2) ->
    N = random:uniform(length(L1)),
    {H,T} = take_nth(N, L1, []),
    warp_word(T, [H|L2]).

take_nth(1, [H|T], L) -> {H, T ++ L};
take_nth(N, [H|T], L) -> take_nth(N-1, T, [H|L]).