Main data types

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

A substitution of Types for TyVars and Kinds for KindVars

An environment for substituting for Ids

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.

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

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

See substTy.

See substCo

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]

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

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

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

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

Find the substitution for an Id in the Subst

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

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

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

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

Adds multiple Id substitutions to the Subst: see also extendIdSubst

Adds multiple TyVar substitutions to the Subst: see also extendTvSubst

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

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

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

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

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

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

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.

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

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.

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

Substitute in a mutually recursive group of Ids

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

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

Clone a mutually recursive group of Ids