Hi,
Quick question - is it possible to put type class contexts on
existentially quantified variables in GADTs defined using record syntax?
E.g.
data ProofContext where
(Reify a, Reify x) => ProofContext {
pcProofScriptInProgress :: RPath ProofStep a ExprRoot,
pcCursor :: Cursor x a
} :: ProofContext
GHC (6.8.2) parse errors on this,
and
data ProofContext where
ProofContext {
pcProofScriptInProgress :: RPath ProofStep a ExprRoot,
pcCursor :: Cursor x a
} :: (Reify a, Reify x) => ProofContext
this is malformed.
ProofContext.hs:20:2:
Malformed constructor result type:
(Reify a, Reify x) => ProofContext
In the result type of a data constructor:
(Reify a, Reify x) => ProofContext
In the data type declaration for `ProofContext'
make: *** [toral] Error 1
Can I also double check that the 'a' variable really is the same 'a' for
the last two fields?
Many thanks,
Tristan Allwood
_______________________________________________
Cvs-ghc mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/cvs-ghc
