Adam Zachary Wyner wrote:
Hi All,
After some weeks of experimenting and digging around, I understand that functions cannot be compared for equality. Thanks to Bjorn Lisper for pointing this out. I basically understand (?) the underlying mathematical issue, which is that functions in general may have infinite domains...
Other suggestions?
You can define equality for functions with finite domains. See the enclosed Haskell module. Loading package base ... linking ... done. Compiling Finite ( Finite.hs, interpreted ) Ok, modules loaded: Finite. *Finite> not == not True *Finite> (&&) == (&&) True *Finite> (&&) == (||) False -- Thomas H module Finite where instance (Finite a, Eq b) => Eq (a->b) where f == g = and [ f x == g x | x <- allValues ] -- A class for finite types class Finite a where allValues :: [a] instance Finite () where allValues = [()] instance Finite Bool where allValues = [False,True] --instance Finite Ordering where ... --instance Finite Char where ... --instance Finite Int where ... instance (Finite a,Finite b) => Finite (a,b) where allValues = [ (x,y) | x<-allValues, y<-allValues] instance Finite a => Finite (Maybe a) where allValues = Nothing:[Just x|x<-allValues] instance (Finite a,Finite b) => Finite (Either a b) where allValues = [Left x|x<-allValues]++[Right y|y<-allValues] -- ...