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@merijn
merijn / gist:6130082
Last active January 2, 2019 10:07
Type family that disallows certain types for type variables.
{-# LANGUAGE ConstraintKinds, DataKinds, PolyKinds, TypeFamilies, TypeOperators #-}
import GHC.Exts (Constraint)
type family Restrict (a :: k) (as :: [k]) :: Constraint where
Restrict a (a ': as) = ("Error!" ~ "Tried to apply a restricted type!")
Restrict x (a ': as) = Restrict x as
Restrict x '[] = ()
foo :: Restrict a [(), Int] => a -> a
@bishboria
bishboria / springer-free-maths-books.md
Last active June 8, 2024 06:39
Springer made a bunch of books available for free, these were the direct links