CoreSubst

Main data types

data Subst

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

Some invariants apply to how you use the substitution:

1. The in-scope set contains at least those Ids and TyVars 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.
2. 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

Constructors

Subst InScopeSet IdSubstEnv TvSubstEnv CvSubstEnv

Instances

Outputable Subst

Methods

ppr :: Subst -> SDoc

pprPrec :: Rational -> 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 "Secrets of the Glasgow Haskell Compiler inliner" Section 3.2 provides the motivation for this abstraction.

Instances

Outputable InScopeSet

Methods

ppr :: InScopeSet -> SDoc

pprPrec :: Rational -> 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

substSpec :: Subst -> Id -> RuleInfo -> RuleInfo

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

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

substTy :: Subst -> Type -> Type

See substTy

substCo :: Subst -> Coercion -> Coercion

See substCo

substExpr :: SDoc -> Subst -> CoreExpr -> CoreExpr

substExprSC :: SDoc -> Subst -> CoreExpr -> CoreExpr

Apply a substitution to an entire CoreExpr. Remember, you may only apply the substitution once: see CoreSubst

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

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

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

substBindSC :: 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

substUnfoldingSC :: Subst -> Unfolding -> Unfolding

Substitutes for the Ids within an unfolding

lookupIdSubst :: SDoc -> Subst -> Id -> CoreExpr

Find the substitution for an Id in the Subst

lookupTCvSubst :: Subst -> TyVar -> Type

Find the substitution for a TyVar in the Subst

substIdOcc :: Subst -> Id -> Id

substTickish :: Subst -> Tickish Id -> Tickish Id

substDVarSet :: 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 CoreSubst

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 the CoreSubst is true 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 Vars that might have been built up while preserving the in-scope set

addInScopeSet :: Subst -> VarSet -> Subst

Add the Var to the in-scope set, but do not remove any existing substitutions for it

extendInScope :: Subst -> Var -> Subst

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

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

Add the Vars 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 the CoreSubst is true after extending the substitution like this.

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

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 is true 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 Var 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 Vars, 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 -> TyVar -> (Subst, TyVar)

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