[Haskell-cafe] Evaluating arithmetic expressions at run time

[Ben Lippmeier]

Andrew Savige wrote:
 > Haskell beginner using GHC.
Hello there!


How about,

opTable
  = [ ("+", (+))
    , ("-", (-)) ... ]

myeval x y op
  = let	Just fun = lookup op opTable
    in   x `fun` y

?


> 
> I have a function to do some simple arithmetic at run time:
> 
> myeval :: Int -> Int -> String -> Int
> myeval x y "+" = (+) x y
> myeval x y "-" = (-) x y
> myeval x y "*" = (*) x y
> -- ...
> 
> While that works, I'm curious to know if it can be done more
> elegantly. I'm thinking of something like:
> 
> myeval :: Int -> Int -> String -> Int
> myeval x y op = (read op) x y
> 
> Thanks,
> /-\
> 
> 
> 
> 		
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