diff options
Diffstat (limited to 'compiler/coreSyn/CoreSubst.hs')
| -rw-r--r-- | compiler/coreSyn/CoreSubst.hs | 34 |
1 files changed, 14 insertions, 20 deletions
diff --git a/compiler/coreSyn/CoreSubst.hs b/compiler/coreSyn/CoreSubst.hs index ae4458bebe..3d2b4b1a10 100644 --- a/compiler/coreSyn/CoreSubst.hs +++ b/compiler/coreSyn/CoreSubst.hs @@ -79,19 +79,9 @@ import Data.List -- -- Some invariants apply to how you use the substitution: -- --- 1. #in_scope_invariant# The in-scope set contains at least those 'Id's and 'TyVar's that will be in scope /after/ --- applying the substitution to a term. Precisely, the in-scope set must be a superset of the free vars of the --- substitution range that might possibly clash with locally-bound variables in the thing being substituted in. +-- 1. Note [The substitution invariant] in TyCoRep -- --- 2. #apply_once# You may apply the substitution only /once/ --- --- There are various ways of setting up the in-scope set such that the first of these invariants hold: --- --- * Arrange that the in-scope set really is all the things in scope --- --- * Arrange that it's the free vars of the range of the substitution --- --- * Make it empty, if you know that all the free vars of the substitution are fresh, and hence can't possibly clash +-- 2. Note [Substitutions apply only once] in TyCoRep data Subst = Subst InScopeSet -- Variables in in scope (both Ids and TyVars) /after/ -- applying the substitution @@ -99,7 +89,7 @@ data Subst TvSubstEnv -- Substitution from TyVars to Types CvSubstEnv -- Substitution from CoVars to Coercions - -- INVARIANT 1: See #in_scope_invariant# + -- INVARIANT 1: See TyCORep Note [The substitution invariant] -- This is what lets us deal with name capture properly -- It's a hard invariant to check... -- @@ -181,7 +171,7 @@ mkEmptySubst in_scope = Subst in_scope emptyVarEnv emptyVarEnv emptyVarEnv mkSubst :: InScopeSet -> TvSubstEnv -> CvSubstEnv -> IdSubstEnv -> Subst mkSubst in_scope tvs cvs ids = Subst in_scope ids tvs cvs --- | Find the in-scope set: see "CoreSubst#in_scope_invariant" +-- | Find the in-scope set: see TyCORep Note [The substitution invariant] substInScope :: Subst -> InScopeSet substInScope (Subst in_scope _ _ _) = in_scope @@ -191,7 +181,8 @@ zapSubstEnv :: Subst -> Subst zapSubstEnv (Subst in_scope _ _ _) = Subst in_scope emptyVarEnv emptyVarEnv emptyVarEnv -- | Add a substitution for an 'Id' to the 'Subst': you must ensure that the in-scope set is --- such that the "CoreSubst#in_scope_invariant" is true after extending the substitution like this +-- such that TyCORep Note [The substitution invariant] +-- holds after extending the substitution like this extendIdSubst :: Subst -> Id -> CoreExpr -> Subst -- ToDo: add an ASSERT that fvs(subst-result) is already in the in-scope set extendIdSubst (Subst in_scope ids tvs cvs) v r @@ -207,8 +198,8 @@ extendIdSubstList (Subst in_scope ids tvs cvs) prs -- | Add a substitution for a 'TyVar' to the 'Subst' -- The 'TyVar' *must* be a real TyVar, and not a CoVar -- You must ensure that the in-scope set is such that --- the "CoreSubst#in_scope_invariant" is true after extending --- the substitution like this. +-- TyCORep Note [The substitution invariant] holds +-- after extending the substitution like this. extendTvSubst :: Subst -> TyVar -> Type -> Subst extendTvSubst (Subst in_scope ids tvs cvs) tv ty = ASSERT( isTyVar tv ) @@ -221,8 +212,10 @@ extendTvSubstList subst vrs where extend subst (v, r) = extendTvSubst subst v r --- | Add a substitution from a 'CoVar' to a 'Coercion' to the 'Subst': you must ensure that the in-scope set is --- such that the "CoreSubst#in_scope_invariant" is true after extending the substitution like this +-- | Add a substitution from a 'CoVar' to a 'Coercion' to the 'Subst': +-- you must ensure that the in-scope set satisfies +-- TyCORep Note [The substitution invariant] +-- after extending the substitution like this extendCvSubst :: Subst -> CoVar -> Coercion -> Subst extendCvSubst (Subst in_scope ids tvs cvs) v r = ASSERT( isCoVar v ) @@ -345,7 +338,8 @@ instance Outputable Subst where -} -- | Apply a substitution to an entire 'CoreExpr'. Remember, you may only --- apply the substitution /once/: see "CoreSubst#apply_once" +-- apply the substitution /once/: +-- see Note [Substitutions apply only once] in TyCoRep -- -- Do *not* attempt to short-cut in the case of an empty substitution! -- See Note [Extending the Subst] |