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{-# LANGUAGE DataKinds, TypeOperators, TypeFamilies #-}
{-# OPTIONS_GHC -fwarn-redundant-constraints #-}
module TcTypeNatSimple where
import GHC.TypeLits
import Data.Proxy
type family SomeFun (n :: Nat)
-- See the Trac ticket; whether this succeeds or fails is distinctly random
-- upon creation, commit f861fc6ad8e5504a4fecfc9bb0945fe2d313687c, this failed
-- with Simon's optimization to the flattening algorithm, commit
-- 37b3646c9da4da62ae95aa3a9152335e485b261e, this succeeded
-- with the change to stop Deriveds from rewriting Deriveds (around Dec. 12, 2014),
-- this failed again
-- 2016-01-23: it just started passing again, when
-- -fwarn-redundant-constraints was removed from the default warning set.
-- Turning the warning back on for this module, ghc reports (and probably has
-- for some time):
-- Redundant constraints: (x <= y, y <= x)
-- In the type signature for:
-- ti7 :: (x <= y, y <= x) => Proxy (SomeFun x) -> Proxy y -> ()
ti7 :: (x <= y, y <= x) => Proxy (SomeFun x) -> Proxy y -> ()
ti7 _ _ = ()
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