Main data types

A substitution environment, containing both Id and TyVar 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

A substitition of Types for TyVars

An environment for substituting for Ids

A set of variables that are in scope at some point

De-shadowing the program is sometimes a useful pre-pass. It can be done simply by running over the bindings with an empty substitution, becuase 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 WorkerInfo given the new function Id

See substTy

Apply a substititon to an entire CoreExpr. Rememeber, 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]

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

Substitutes for the Ids within an unfolding

Find the substitution for an Id in the Subst

Find the substitution for a TyVar in the 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

Find the in-scope set: see CoreSubst

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

Adds multiple Id substitutions to the Subst: see also extendIdSubst

Add a substitution for a TyVar to the Subst: you must ensure that the in-scope set is such that the CoreSubst is true after extending the substitution like this

Adds multiple TyVar substitutions to the Subst: see also extendTvSubst

Add a substitution for a TyVar or Id as appropriate to the Var being added. See also extendIdSubst and extendTvSubst

Add a substitution for a TyVar or Id as appropriate to all the Vars being added. See also extendSubst

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

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

Add the Vars 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

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

Applies substBndr to a number of Vars, 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