GHC.Core.Subst

Main data types

data Subst

A substitution environment, containing Id, TyVar, and CoVar substitutions.

Some invariants apply to how you use the substitution:

1. Note [The substitution invariant] in GHC.Core.TyCo.Subst
2. Note [Substitutions apply only once] in GHC.Core.TyCo.Subst

Constructors

Subst InScopeSet IdSubstEnv TvSubstEnv CvSubstEnv

Instances

Outputable Subst

Defined in GHC.Core.Subst

Methods

ppr :: Subst -> SDoc

type TvSubstEnv = TyVarEnv Type

A substitution of Types for TyVars and Kinds for KindVars

type IdSubstEnv = IdEnv CoreExpr

An environment for substituting for Ids

data InScopeSet

A set of variables that are in scope at some point.

Note that this is a superset of the variables that are currently in scope. See Note [The InScopeSet invariant].

"Secrets of the Glasgow Haskell Compiler inliner" Section 3.2 provides the motivation for this abstraction.

Instances

Outputable InScopeSet

Defined in GHC.Types.Var.Env

Methods

ppr :: InScopeSet -> SDoc

Substituting into expressions and related types

deShadowBinds :: CoreProgram -> CoreProgram

De-shadowing the program is sometimes a useful pre-pass. It can be done simply by running over the bindings with an empty substitution, because substitution returns a result that has no-shadowing guaranteed.

(Actually, within a single type there might still be shadowing, because substTy is a no-op for the empty substitution, but that's probably OK.)

Aug 09

This function is not used in GHC at the moment, but seems so short and simple that I'm going to leave it here

substRuleInfo :: Subst -> Id -> RuleInfo -> RuleInfo

Substitutes for the Ids within the RuleInfo given the new function Id

substRulesForImportedIds :: Subst -> [CoreRule] -> [CoreRule]

substTy :: Subst -> Type -> Type

See substTy.

substCo :: HasCallStack => Subst -> Coercion -> Coercion

See substCo

substExpr :: HasDebugCallStack => Subst -> CoreExpr -> CoreExpr

substExpr applies a substitution to an entire CoreExpr. Remember, you may only apply the substitution once: See Note [Substitutions apply only once] in GHC.Core.TyCo.Subst

Do *not* attempt to short-cut in the case of an empty substitution! See Note [Extending the Subst]

substExprSC :: HasDebugCallStack => Subst -> CoreExpr -> CoreExpr

substBind :: HasDebugCallStack => Subst -> CoreBind -> (Subst, CoreBind)

Apply a substitution to an entire CoreBind, additionally returning an updated Subst that should be used by subsequent substitutions.

substBindSC :: HasDebugCallStack => Subst -> CoreBind -> (Subst, CoreBind)

Apply a substitution to an entire CoreBind, additionally returning an updated Subst that should be used by subsequent substitutions.

substUnfolding :: Subst -> Unfolding -> Unfolding

Substitutes for the Ids within an unfolding NB: substUnfolding discards any unfolding without without a Stable source. This is usually what we want, but it may be a bit unexpected

substUnfoldingSC :: Subst -> Unfolding -> Unfolding

Substitutes for the Ids within an unfolding NB: substUnfolding discards any unfolding without without a Stable source. This is usually what we want, but it may be a bit unexpected

lookupIdSubst :: HasDebugCallStack => Subst -> Id -> CoreExpr

Find the substitution for an Id in the Subst

substIdType :: Subst -> Id -> Id

substIdOcc :: Subst -> Id -> Id

substTickish :: Subst -> CoreTickish -> CoreTickish

substDVarSet :: HasDebugCallStack => Subst -> DVarSet -> DVarSet

substIdInfo :: Subst -> Id -> IdInfo -> Maybe IdInfo

Substitute into some IdInfo with regard to the supplied new Id.

Operations on substitutions

emptySubst :: Subst

mkEmptySubst :: InScopeSet -> Subst

mkSubst :: InScopeSet -> TvSubstEnv -> CvSubstEnv -> IdSubstEnv -> Subst

mkOpenSubst :: InScopeSet -> [(Var, CoreArg)] -> Subst

Simultaneously substitute for a bunch of variables No left-right shadowing ie the substitution for (x y. e) a1 a2 so neither x nor y scope over a1 a2

substInScope :: Subst -> InScopeSet

Find the in-scope set: see GHC.Core.TyCo.Subst Note [The substitution invariant]

isEmptySubst :: Subst -> Bool

extendIdSubst :: Subst -> Id -> CoreExpr -> Subst

Add a substitution for an Id to the Subst: you must ensure that the in-scope set is such that TyCoSubst Note [The substitution invariant] holds after extending the substitution like this

extendIdSubstList :: Subst -> [(Id, CoreExpr)] -> Subst

Adds multiple Id substitutions to the Subst: see also extendIdSubst

extendTCvSubst :: TCvSubst -> TyCoVar -> Type -> TCvSubst

extendTvSubstList :: Subst -> [(TyVar, Type)] -> Subst

Adds multiple TyVar substitutions to the Subst: see also extendTvSubst

extendSubst :: Subst -> Var -> CoreArg -> Subst

Add a substitution appropriate to the thing being substituted (whether an expression, type, or coercion). See also extendIdSubst, extendTvSubst, extendCvSubst

extendSubstList :: Subst -> [(Var, CoreArg)] -> Subst

Add a substitution as appropriate to each of the terms being substituted (whether expressions, types, or coercions). See also extendSubst.

extendSubstWithVar :: Subst -> Var -> Var -> Subst

zapSubstEnv :: Subst -> Subst

Remove all substitutions for Ids and Exprs that might have been built up while preserving the in-scope set

extendInScope :: Subst -> Var -> Subst

Add the Expr to the in-scope set: as a side effect, and remove any existing substitutions for it

extendInScopeList :: Subst -> [Var] -> Subst

Add the Exprs to the in-scope set: see also extendInScope

extendInScopeIds :: Subst -> [Id] -> Subst

Optimized version of extendInScopeList that can be used if you are certain all the things being added are Ids and hence none are TyVars or CoVars

isInScope :: Var -> Subst -> Bool

setInScope :: Subst -> InScopeSet -> Subst

getTCvSubst :: Subst -> TCvSubst

extendTvSubst :: Subst -> TyVar -> Type -> Subst

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 GHC.Core.TyCo.Subst Note [The substitution invariant] holds after extending the substitution like this.

extendCvSubst :: Subst -> CoVar -> Coercion -> Subst

Add a substitution from a CoVar to a Expr to the Subst: you must ensure that the in-scope set satisfies GHC.Core.TyCo.Subst Note [The substitution invariant] after extending the substitution like this

delBndr :: Subst -> Var -> Subst

delBndrs :: Subst -> [Var] -> Subst

Substituting and cloning binders

substBndr :: Subst -> Var -> (Subst, Var)

Substitutes a Expr for another one according to the Subst given, returning the result and an updated Subst that should be used by subsequent substitutions. IdInfo is preserved by this process, although it is substituted into appropriately.

substBndrs :: Subst -> [Var] -> (Subst, [Var])

Applies substBndr to a number of Exprs, accumulating a new Subst left-to-right

substRecBndrs :: Subst -> [Id] -> (Subst, [Id])

Substitute in a mutually recursive group of Ids

substTyVarBndr :: Subst -> TyVar -> (Subst, TyVar)

substCoVarBndr :: Subst -> CoVar -> (Subst, CoVar)

cloneBndr :: Subst -> Unique -> Var -> (Subst, Var)

cloneBndrs :: Subst -> UniqSupply -> [Var] -> (Subst, [Var])

cloneIdBndr :: Subst -> UniqSupply -> Id -> (Subst, Id)

Very similar to substBndr, but it always allocates a new Unique for each variable in its output. It substitutes the IdInfo though.

cloneIdBndrs :: Subst -> UniqSupply -> [Id] -> (Subst, [Id])

Applies cloneIdBndr to a number of Ids, accumulating a final substitution from left to right

cloneRecIdBndrs :: Subst -> UniqSupply -> [Id] -> (Subst, [Id])

Clone a mutually recursive group of Ids