Re: [Haskell-cafe] type inference question

minh thu wrote:

Also, I'd like to know why

id id True

is permitted but not

(\f -> f f True) id

Because this requires rank-2 types:

Prelude> :set -XScopedTypeVariables Prelude> :set -XRank2Types Prelude> (\(f :: forall a. a -> a) -> f f True) id True

HTH, Martijn.