[Haskell-beginners] Evaluation oddity

Hi all, maybe one of you sees a difference, I sure don’t… The full code for this is below. When I call *Main> diffieH 23 16 20 13 and use the result in *Main> encipher "abc" 13 „nop" I get the letters to be expected. However, when I combine these into

start text p a b = encipher text (diffieH p a b)

*Main> start "abc" 23 16 20 „efg" the result changes. Any hints are most welcome. Thank you and regards Torsten

import Data.Char

diffieH p a b = (b ^ a) `mod` p

number2letter number = chr (number + 96) letter2number letter = (ord letter) - 96

start text p a b = encipher text (diffieH p a b)

encipher [] _ = [] encipher (b:rest) key = (number2letter (((letter2number b)+key) `mod` 26)) : (encipher rest key)