match_co: needs more cases

[Simon Peyton-Jones]

It's harmless. But it's there to tell us that a RULE is not going to match because the LHS involves a coercion that is not Refl or a variable.   Matching on more complex coercions is likely to be fragile, since they can take a variety of forms.

So don't worry too much, but I'd be interested in a repro case

Simon

| -----Original Message-----
| From: glasgow-haskell-users-bounces at haskell.org [mailto:glasgow-haskell-
| users-bounces at haskell.org] On Behalf Of Evan Laforge
| Sent: 27 May 2013 18:56
| To: GHC users
| Subject: match_co: needs more cases
| 
| I made some strictifying changes and started getting this msg from ghc:
| 
| match_co: needs more cases
|     vector-0.10.0.1:Data.Vector.Generic.Mutable.MVector{tc r46}
|       (Sym <(vector-0.10.0.1:Data.Vector.TFCo:R:MutableVector{tc r45})>)
|       <main:Util.TimeVectorStorable.Sample{tc r4e} y{tv a4lK} [tv]>
| 
| It's not just TimeVectorStorable.Sample (which is indeed stored in
| Data.Vectors), we also have some mysterious compiler-generated
| symbols:
| 
| match_co: needs more cases
|     vector-0.10.0.1:Data.Vector.Generic.Mutable.MVector{tc rQA}
|       (Sym <(vector-0.10.0.1:Data.Vector.TFCo:R:MutableVector{tc rQz})>)
|       <a{tv a6IH} [tv]>
| 
| I assume this is harmless, but I didn't see any other references to
| this error on the web or on the ghc trac so maybe it's new?
| 
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