Re: [Haskell-cafe] Evaluating arithmetic expressions at run time

28 Jan 2006

      BTW: There isn't an easy way to magically derive opTable. We're relying 
on the fact that these simple functions all have the same type.

Ben Lippmeier wrote:
...
opTable
 = [ ("+", (+))
   , ("-", (-)) ... ]
myeval x y op
 = let    Just fun = lookup op opTable
   in   x `fun` y
You could also do

myeval x y op
  = case op of
	"+"	-> x + y
	"-"	-> x - y
...

is probably the "smallest" way.

Ben.