File: Fac.curry

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curry-tools 1.0.1%2Bdfsg1-1
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{-# OPTIONS_CYMAKE -F --pgmF=currypp --optF=contracts #-}

-- Defining factorial numbers:

-- Specification: the usual recursive definition
fac'spec n = if n==0 then 1 else n * fac'spec (n-1)

-- The input should be non-negative:
fac'pre n = n>=0
-- The result should be positive:
fac'post _ v = v>0

-- An implementation using Prelude operations:
fac n = foldr (*) 1 [1..n]