workaround hrt

workaround higher rank

WIP: inferencing higher rank types

Merge branch 'master' of ssh://github.com/RemuLang/proud

progress: multi-level type env for convenient generalising

equivalent tv kept in a set with forward refs, which helps generalising

migrate to own unification & use new unification algo

refactored

refactor

lambda cannot be automatically polymorphic. unification framework should make some modification, to record the creation of type variables, and distinguish the type variables occurred in given scope

better abstractions for supporting advanced polymorphisms

module refactored

qualified type

clarify generalising algorithm

refactor: share states when compiling & generalising unification