Retrie.AlphaEnv

Documentation

data AlphaEnv

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.

alphaEnvOffset :: AlphaEnv -> Int

emptyAlphaEnv :: AlphaEnv

extendAlphaEnv :: RdrName -> AlphaEnv -> AlphaEnv

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.

lookupAlphaEnv :: RdrName -> AlphaEnv -> Maybe Int

pruneAlphaEnv :: Int -> AlphaEnv -> AlphaEnv

For Internal Use Only

extendAlphaEnvInternal :: RdrName -> AlphaEnv -> AlphaEnv

For internal use of PatternMap methods.