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darkf/rpn.hs

Created December 29, 2012 03:01
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My Haskell is horrible
Raw
rpn.hs
data Tok = Op Char | NumTok Int
op '+' = (+)
op '*' = (*)
op _ = \_ _ -> 666
eval toks =
eval' toks []
where
eval' [] s = head s
eval' (NumTok x:xs) s = eval' xs (x:s)
eval' (Op x:xs) (rhs:lhs:s) =
eval' xs $ ((op x) lhs rhs):s
main = print $ eval $ [NumTok 3, NumTok 2, Op '+', NumTok 2, Op '*', NumTok 2, Op '*']
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