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monoid/q.hs

Created August 27, 2011 09:35
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Old hack: list queue
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q.hs
data Q a = Q [a] [a] deriving Show -- head and reversed tail
emptyQ = Q [] []
enQ a (Q h t) = Q h (a:t)
popQ (Q [] []) = error "Empty queue"
popQ (Q (a:h) t) = (a, Q h t)
popQ (Q [] t) = popQ (Q (reverse t) [])
toList (Q h t) = h ++ (reverse t)
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