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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/hsSyn/Convert.lhs | |
| 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/hsSyn/Convert.lhs')
| -rw-r--r-- | compiler/hsSyn/Convert.lhs | 15 |
1 files changed, 10 insertions, 5 deletions
diff --git a/compiler/hsSyn/Convert.lhs b/compiler/hsSyn/Convert.lhs index 8caf987336..a07fafe00d 100644 --- a/compiler/hsSyn/Convert.lhs +++ b/compiler/hsSyn/Convert.lhs @@ -215,7 +215,7 @@ cvtDec (FamilyD flav tc tvs kind) ; kind' <- cvtMaybeKind kind ; returnL $ TyClD (FamDecl (FamilyDecl (cvtFamFlavour flav) tc' tvs' kind')) } where - cvtFamFlavour TypeFam = TypeFamily + cvtFamFlavour TypeFam = OpenTypeFamily cvtFamFlavour DataFam = DataFamily cvtDec (DataInstD ctxt tc tys constrs derivs) @@ -243,13 +243,18 @@ cvtDec (NewtypeInstD ctxt tc tys constr derivs) { dfid_inst = DataFamInstDecl { dfid_tycon = tc', dfid_pats = typats' , dfid_defn = defn, dfid_fvs = placeHolderNames } }} -cvtDec (TySynInstD tc eqns) +cvtDec (TySynInstD tc eqn) = do { tc' <- tconNameL tc - ; eqns' <- mapM (cvtTySynEqn tc') eqns + ; eqn' <- cvtTySynEqn tc' eqn ; returnL $ InstD $ TyFamInstD - { tfid_inst = TyFamInstDecl { tfid_eqns = eqns' - , tfid_group = (length eqns' /= 1) + { tfid_inst = TyFamInstDecl { tfid_eqn = eqn' , tfid_fvs = placeHolderNames } } } + +cvtDec (ClosedTypeFamilyD tc tyvars mkind eqns) + = do { (_, tc', tvs') <- cvt_tycl_hdr [] tc tyvars + ; mkind' <- cvtMaybeKind mkind + ; eqns' <- mapM (cvtTySynEqn tc') eqns + ; returnL $ TyClD (FamDecl (FamilyDecl (ClosedTypeFamily eqns') tc' tvs' mkind')) } ---------------- cvtTySynEqn :: Located RdrName -> TySynEqn -> CvtM (LTyFamInstEqn RdrName) cvtTySynEqn tc (TySynEqn lhs rhs) |