On Sun, May 20, 2012 at 8:28 AM, Stuart Hungerford wrote:

Hi,

Suppose I have a module of functions with identical signatures:

module Functions where

a :: Int -> [Int]

a x = [x + 1, x + 2, x + 3]

b :: Int -> [Int]

b x = [x + 4, x + 5, x + 6]

and in my main function I receive a command line arguments (a string) naming one of the functions in MyModule. I'd like to lookup and use of the functions by name:

lookup :: String -> (Int -> [Int])

lookup "a" = MyModule.a

lookup "b" = MyModule.b

...

Is there a more idiomatic Haskell way of going about this?  I can see there's a fundamental tension between a runtime choice of function name expressed as a string and the need for compile-time known function choice.

Since the two functions have the same type there is no problem to do this, and in fact you have already hinted at a reasonable solution yourself: create an assoctiation list and use lookup (http://is.gd/wZPlNJ). /M -- Magnus Therning                      OpenPGP: 0xAB4DFBA4 email: magnus@therning.org   jabber: magnus@therning.org twitter: magthe               http://therning.org/magnus