Re: Suppressing False Incomplete Pattern Matching Warnings for Polymorphic Pattern Synonyms

This sounds like an infelicity in COMPLETE pragmas. Do we have a documented reason why fixing this is impossible? Richard

On Oct 25, 2018, at 7:36 AM, Shayan Najd wrote:

Dear GHC hackers,

On our work on the new front-end AST for GHC [0] based on TTG [1], we would like to use a pattern synonym like the following [2]:

{{{ pattern LL :: HasSrcSpan a => SrcSpan -> SrcSpanLess a -> a pattern LL s m <- (decomposeSrcSpan -> (m , s)) where LL s m = composeSrcSpan (m , s) }}}

We know that any match on `LL` patterns, makes the pattern matching total, as it uses a view pattern with a total output pattern (i.e., in `decomposeSrcSpan -> (m , s)`, the pattern `(m , s)` is total).

As far as I understand, currently COMPLETE pragmas cannot be used with such a polymorphic pattern.

What do you suggest us to do to avoid the false incomplete pattern matching warnings?

Thanks, Shayan

[0] https://ghc.haskell.org/trac/ghc/wiki/ImplementingTreesThatGrow [1] https://ghc.haskell.org/trac/ghc/wiki/ImplementingTreesThatGrow/TreesThatGro... [2] https://ghc.haskell.org/trac/ghc/wiki/ImplementingTreesThatGrow/HandlingSour... _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs