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forall in Scala

As @Michael Kohl commented, this use of forall in Haskell is an existential type and can be exactly replicted in Scala using either the forSome construct or a wildcard. That means that @paradigmatic’s answer is largely correct. Nevertheless there’s something missing there relative to the Haskell original which is that instances of its ShowBox type … Read more

What does the `forall` keyword in Haskell/GHC do?

Let’s start with a code example: foob :: forall a b. (b -> b) -> b -> (a -> b) -> Maybe a -> b foob postProcess onNothin onJust mval = postProcess val where val :: b val = maybe onNothin onJust mval This code doesn’t compile (syntax error) in plain Haskell 98. It requires … Read more