#4841: TypeSynonymInstances allow some flexible instances
---------------------------------+------------------------------------------
Reporter: benmachine | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 7.0.1 | Keywords:
Testcase: | Blockedby:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: GHC accepts invalid program
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The docs for !TypeSynonymInstances say:
As always, using a type synonym is just shorthand for writing the RHS of
the type synonym definition.
However, there are instances that can be defined with ''only''
!TypeSynonymInstances enabled that cannot be defined without it. The
following compiles:
{{{
{-# LANGUAGE TypeSynonymInstances #-}
instance Bounded String where
minBound = ""
maxBound = maxBound : maxBound
}}}
even though the same with `[Char]` does not.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4841>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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