Sascha Böhme wrote:
Hello,
referring to the Haskell 98 report as available in the Internet, I
have a short question. Section 4.1.3 (Syntax of Class Assertions
and Contexts) contains the rule:
class -> qtycls tyvar
| qtycls ( tyvar atype1 ... atypen ) (n>=1)
Is there a (simple) practical example of a Haskell type expression
using the second line of the above rule?
If you read a little bit further, you'll find the type
(Eq (f a), Functor f) => (a -> b) -> f a -> f b -> Bool
in Sect 4.1.4. Another example can be found in Sect. 4.5.3:
f :: (Monad m, Eq (m a)) => a -> m a -> Bool
f x y = return x == y
Regards
Wolfgang
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