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| author | Richard Eisenberg <eir@cis.upenn.edu> | 2013-06-21 13:54:49 +0100 |
|---|---|---|
| committer | Richard Eisenberg <eir@cis.upenn.edu> | 2013-06-21 13:54:49 +0100 |
| commit | 569b26526403df4d88fe2a6d64c7dade09d003ad (patch) | |
| tree | f216a5ceaf5d655248564abefab6765aaa9da37d /compiler/main/PprTyThing.hs | |
| parent | 11db9cf82e014de43d8ab04947ef2a2b7fa30f37 (diff) | |
| download | haskell-569b26526403df4d88fe2a6d64c7dade09d003ad.tar.gz | |
Revise implementation of overlapping type family instances.
This commit changes the syntax and story around overlapping type
family instances. Before, we had "unbranched" instances and
"branched" instances. Now, we have closed type families and
open ones.
The behavior of open families is completely unchanged. In particular,
coincident overlap of open type family instances still works, despite
emails to the contrary.
A closed type family is declared like this:
> type family F a where
> F Int = Bool
> F a = Char
The equations are tried in order, from top to bottom, subject to
certain constraints, as described in the user manual. It is not
allowed to declare an instance of a closed family.
Diffstat (limited to 'compiler/main/PprTyThing.hs')
| -rw-r--r-- | compiler/main/PprTyThing.hs | 13 |
1 files changed, 9 insertions, 4 deletions
diff --git a/compiler/main/PprTyThing.hs b/compiler/main/PprTyThing.hs index 5145f56005..56d7afc4fa 100644 --- a/compiler/main/PprTyThing.hs +++ b/compiler/main/PprTyThing.hs @@ -29,7 +29,8 @@ import GHC ( TyThing(..) ) import DataCon import Id import TyCon -import Coercion( pprCoAxiom ) +import Coercion( pprCoAxiom, pprCoAxBranch ) +import CoAxiom( CoAxiom(..), brListMap ) import HscTypes( tyThingParent_maybe ) import Type( tidyTopType, tidyOpenType ) import TypeRep( pprTvBndrs ) @@ -175,10 +176,14 @@ pprTyCon :: PrintExplicitForalls -> ShowSub -> TyCon -> SDoc pprTyCon pefas ss tyCon | Just syn_rhs <- GHC.synTyConRhs_maybe tyCon = case syn_rhs of - SynFamilyTyCon {} -> pprTyConHdr pefas tyCon <+> dcolon <+> - pprTypeForUser pefas (GHC.synTyConResKind tyCon) + OpenSynFamilyTyCon -> pprTyConHdr pefas tyCon <+> dcolon <+> + pprTypeForUser pefas (GHC.synTyConResKind tyCon) + ClosedSynFamilyTyCon (CoAxiom { co_ax_branches = branches }) -> + hang (pprTyConHdr pefas tyCon <+> dcolon <+> + pprTypeForUser pefas (GHC.synTyConResKind tyCon) <+> ptext (sLit "where")) + 2 (vcat (brListMap (pprCoAxBranch tyCon) branches)) SynonymTyCon rhs_ty -> hang (pprTyConHdr pefas tyCon <+> equals) - 2 (ppr rhs_ty) -- Don't suppress foralls on RHS type! + 2 (ppr rhs_ty) -- Don't suppress foralls on RHS type! -- e.g. type T = forall a. a->a | Just cls <- GHC.tyConClass_maybe tyCon = pprClass pefas ss cls |