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| author | Simon Peyton Jones <simonpj@microsoft.com> | 2016-11-10 15:52:31 +0000 |
|---|---|---|
| committer | Simon Peyton Jones <simonpj@microsoft.com> | 2016-11-10 16:03:43 +0000 |
| commit | f05d685ae05ec293083f2fa7ec7ba057fbe64869 (patch) | |
| tree | 205bb483bebc46be61af826ed3aef7ca08987155 | |
| parent | 7fe71636dc14a219c26def5cac2da9fa20689540 (diff) | |
| download | haskell-f05d685ae05ec293083f2fa7ec7ba057fbe64869.tar.gz | |
Refactoring of mkNewTypeEqn
The refactoring here is very small. I did it while studying
Trac #12814.
To implement the change in #12814, we can just un-comment the
lines at line 1275. It's ready to go but I didn't want to pull
the trigger in this commit
| -rw-r--r-- | compiler/typecheck/TcDeriv.hs | 37 |
1 files changed, 19 insertions, 18 deletions
diff --git a/compiler/typecheck/TcDeriv.hs b/compiler/typecheck/TcDeriv.hs index 4722f16354..0ff70fda79 100644 --- a/compiler/typecheck/TcDeriv.hs +++ b/compiler/typecheck/TcDeriv.hs @@ -1256,6 +1256,7 @@ mkNewTypeEqn dflags overlap_mode tvs -- Next we figure out what superclass dictionaries to use -- See Note [Newtype deriving superclasses] above + sc_theta :: [PredOrigin] cls_tyvars = classTyVars cls dfun_tvs = tyCoVarsOfTypesWellScoped inst_tys inst_ty = mkTyConApp tycon tc_args @@ -1264,24 +1265,24 @@ mkNewTypeEqn dflags overlap_mode tvs substTheta (zipTvSubst cls_tyvars inst_tys) $ classSCTheta cls - -- Next we collect Coercible constraints between - -- the Class method types, instantiated with the representation and the - -- newtype type; precisely the constraints required for the - -- calls to coercible that we are going to generate. - coercible_constraints = - [ let (Pair t1 t2) = mkCoerceClassMethEqn cls dfun_tvs inst_tys rep_inst_ty meth - in mkPredOrigin (DerivOriginCoerce meth t1 t2) TypeLevel - (mkReprPrimEqPred t1 t2) - | meth <- classMethods cls ] - - -- If there are no tyvars, there's no need - -- to abstract over the dictionaries we need - -- Example: newtype T = MkT Int deriving( C ) - -- We get the derived instance - -- instance C T - -- rather than - -- instance C Int => C T - all_preds = rep_pred_o : coercible_constraints ++ sc_theta -- NB: rep_pred comes first + -- Next we collect constraints for the class methods + -- If there are no methods, we don't need any constraints + -- Otherwise we need (C rep_ty), for the representation methods, + -- and constraints to coerce each individual method + meth_theta :: [PredOrigin] + meths = classMethods cls + meth_theta = rep_pred_o : coercible_constraints +-- meth_theta | null meths = [] -- No methods => no constraints (Trac #12814) +-- | otherwise = rep_pred_o : coercible_constraints + coercible_constraints + = [ mkPredOrigin (DerivOriginCoerce meth t1 t2) TypeLevel + (mkReprPrimEqPred t1 t2) + | meth <- meths + , let (Pair t1 t2) = mkCoerceClassMethEqn cls dfun_tvs + inst_tys rep_inst_ty meth ] + + all_preds :: [PredOrigin] + all_preds = meth_theta ++ sc_theta ------------------------------------------------------------------- -- Figuring out whether we can only do this newtype-deriving thing |