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| author | sheaf <sam.derbyshire@gmail.com> | 2021-07-30 13:50:25 +0200 |
|---|---|---|
| committer | Marge Bot <ben+marge-bot@smart-cactus.org> | 2021-08-04 16:38:40 -0400 |
| commit | 7a9d8803cfde3c42da4b27a7b89bdcb2ac870e3f (patch) | |
| tree | 0d2e0dd78e719d93e276fff0a668e8315639ff45 /compiler/GHC/Tc/Instance | |
| parent | 477bc2dd6d506ece1c5c030f79f3934ff1922a5f (diff) | |
| download | haskell-7a9d8803cfde3c42da4b27a7b89bdcb2ac870e3f.tar.gz | |
Use Reductions to keep track of rewritings
We define Reduction = Reduction Coercion !Type.
A reduction of the form 'Reduction co new_ty' witnesses an
equality ty ~co~> new_ty.
That is, the rewriting happens left-to-right: the right-hand-side
type of the coercion is the rewritten type, and the left-hand-side
type the original type.
Sticking to this convention makes the codebase more consistent,
helping to avoid certain applications of SymCo.
This replaces the parts of the codebase which represented reductions as
pairs, (Coercion,Type) or (Type,Coercion).
Reduction being strict in the Type argument improves performance
in some programs that rewrite many type families (such as T9872).
Fixes #20161
-------------------------
Metric Decrease:
T5321Fun
T9872a
T9872b
T9872c
T9872d
-------------------------
Diffstat (limited to 'compiler/GHC/Tc/Instance')
| -rw-r--r-- | compiler/GHC/Tc/Instance/Family.hs | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/compiler/GHC/Tc/Instance/Family.hs b/compiler/GHC/Tc/Instance/Family.hs index 4818fd9ad9..a7cdb3d507 100644 --- a/compiler/GHC/Tc/Instance/Family.hs +++ b/compiler/GHC/Tc/Instance/Family.hs @@ -534,7 +534,7 @@ tcLookupDataFamInst_maybe fam_inst_envs tc tc_args -- It does not look through type families. -- It does not normalise arguments to a tycon. -- --- If the result is Just (rep_ty, (co, gres), rep_ty), then +-- If the result is Just ((gres, co), rep_ty), then -- co : ty ~R rep_ty -- gres are the GREs for the data constructors that -- had to be in scope |