{-# OPTIONS_CYMAKE -F --pgmF=currypp --optF=contracts #-} import Test.Prop -- An infinite list of Fibonacci numbers specified by traditional -- recursive definition -- (Deterministic!) specification of all Fibonacci numbers: fibs'spec :: [Int] fibs'spec = map fib [0..] where fib n | n == 0 = 0 | n == 1 = 1 | otherwise = fib (n-1) + fib (n-2) -- In order to check the infinite result list, we define a specific observer: fibs'post'observe xs = take 10 xs -- A more efficient (but erroneous) implementation of all Fibonacci numbers: fibs :: [Int] fibs = fiblist 0 1 where fiblist x y = x : fiblist (x+y) y main = take 4 fibs fibsViolation = toError (take 4 fibs)