Till Doerges writes:

select' :: [a] -> [Integer] -> ([a],[a]) select' xs poss = sAcc xs (sort poss) 0 ([],[]) where sAcc :: [a] -> [Integer] -> Integer -> (([a],[a]) -> ([a],[a])) ...

Crash> select' "test" [0..]

(35922 reductions, 63905 cells) ERROR: Control stack overflow ...

2) Why does "select' "test" [0..]" not work?

You are trying to *sort* the *infinite* list poss=[0..]. -- Janis Voigtlaender http://wwwtcs.inf.tu-dresden.de/~voigt/ mailto:voigt@tcs.inf.tu-dresden.de