[Haskell-cafe] property testing, point-free style

Olaf Klinke olf at aatal-apotheke.de
Wed May 31 11:25:06 UTC 2023

Dear Cafe,

The expression

\x -> f x == g x

is a testable property, as long as values for x can be randomly
generated. For clarity I'd prefer a point-free style, e.g. 

f ≡ g

Are there extensions to QuickCheck that let me write this? The
QuickCheck package itself does not seem to contain such an operator. My
current work-around is a 
    newtype ExtensionalEquality a b 
that holds two functions of type (a -> b) and a Testable instance for
it. But I've got a hunch that I re-invented some wheel here. (My
ExtensionalEquality is isomorphic to 
    Refl (a -> b) (a -> b)
but Refl ist conceptually about type equality, not term equality.)


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