-- Sergio and Michael
-- Tue Apr 12 17:02:35 PDT 2011
-- updated Thu Jul  6 14:02:15 PDT 2017

-- Determine whether there are duplicate values in a list

{-# OPTIONS_CYMAKE -F --pgmF=currypp #-}

import Test.EasyCheck
-- execute with: curry check uniq

-- prototypical implementation
duplND (_++[x]++_++[x]++_) = True
duplND'default _ = False

-- production implementation
duplD [] = False
duplD (x:xs) = aux xs
  where aux (y:ys) = x==y || aux ys || duplD xs
        aux [] = False

--tests
sample = [[1,2,3],[2,3,2,4]]  -- one no, another yes
testND = map duplND sample
testD  = map duplD  sample

prop = testD -=- testND