#3485: "Illegal type synonym family application in instance" error is
unnecessary,
should be removed
-----------------------------+----------------------------------------------
Reporter: Ashley Yakeley | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler (Type checker)
Version: 6.10.4 | Severity: normal
Keywords: | Testcase:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
-----------------------------+----------------------------------------------
GHC shouldn't complain about "Illegal type synonym family application in
instance", since there's an obvious workaround:
{{{
type family Fam t
instance C (Fam Int)
}}}
can become
{{{
type family Fam t
instance (Fam Int ~ famint) => C famint
}}}
The programmer ought to be smart enough to notice that Fam is not a type-
constructor, so "Fam Int" is going to overlap like a type-variable.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3485>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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