isaacdupree at charter.net
Mon Dec 29 15:00:52 EST 2008
Simon Peyton-Jones wrote:
> This is a nasty corner I agree. GHC requires -XGADTs for you to *define* a GADT. Perhaps it should also require -XGADTs for you to *match against* one (as you are doing here). That would avoid this particular hole. If you think that would be a step forward, do put forward a Trac feature request, and encourage others to support it.
Does GHC require any flags to pattern-match against an
existential constructor? (does it require type-system
(and what if GADT syntax was used for an ordinary data type?
or for an ordinary existential?)
but I'd support requiring -XGADTs in any such pattern-match
in which XRelaxedPolyRec could make a difference. Somehow
it doesn't seem fair for a module to imply that it *doesn't*
use GADTs, if it cannot even by type-checked without
also see http://hackage.haskell.org/trac/ghc/ticket/2004
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