to HsBinds, which can't see the defn of HsMatchContext
pprPatBind :: forall bndr id body. (OutputableBndrId bndr,
                                    OutputableBndrId id, Outputable body)
           => LPat bndr -> GRHSs id body -> SDoc
pprPatBind pat (grhss)
 = sep [ppr pat, nest 2 (pprGRHSs (PatBindRhs :: HsMatchContext id) grhss)]

pprMatch :
pprPatBind :: forall bndr id body. (OutputableBndrId bndr,
                                    OutputableBndrId id, Outputable body)
           => LPat bndr -> GRHSs id body -> SDoc
pprPatBind pat (grhss)
 = sep [ppr pat, nest 2 (pprGRHSs (PatBindRhs :: HsMatchContext id) grhss)]
pprPatBind pat (grhss)
 = sep [ppr pat, nest 2 (pprGRHSs (PatBindRhs :: HsMatchContext id) grhss)]