[erlang-questions] View patterns

[ok]

I made a mistake.

     np(K, X) when integer(X), integer(K), X >= K ->
         {X};              %%%% HERE
     np(_, _) ->
         false.

should of course be

     np(K, X) when integer(X), integer(K), X >= K ->
         {X - K};
     np(_, _) ->
         false.

Fix that and all is well.

The real trick with view patterns is to compile them so that you
do not do too much repeated work.