Conditional instances

• “A pair supports == if its component types do”

instance (Eq a,Eq b)=> Eq(a,b) where

(x1,y1)==(x2,y2) = x1=x2 and y1=y2

x /= y = not (x==y)

• A list of a supports == if a does”

instance (Eq a)=> Eq [a] where

[] == [] = True

(x:xs) == (y:ys) = x==y and xs==ys

_ == _ = False

Previous slide

Next slide

Back to first slide

View graphic version