Documentation

Environment used to implement alpha-equivalence checking. As we pass a binder we map it to a de-bruijn index. When we later encounter a variable occurrence, we look it up in the map, and if present, use the index for matching, rather than the name.

For external use to build an initial AlphaEnv for mMatch. We add local bindings to the AlphaEnv and track an offset which we subtract in lookupAlphaEnv. This prevents locally-bound variable occurrences from unifying with free variables in the pattern.

For internal use of PatternMap methods.