lol-typing

Type inferencer for LOL (λω language)

Latest on Hackage:1.20160822

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GPL-3 licensed and maintained by Julien Moutinho

WARNING: this is a research program written as I learn and explore type inferencing: please understand well by yourself whatever you may take from it; any question or contribution being welcome :-)

This package implements type inferencing by manipulating type constraints through 3 successive phases: 1. the Collect phase collects them from some expression, 2. the Order phase modifies the order in which they will be solved, 3. the Solver phase solves them according to the logic of some type inference rules.

So far, the principles within these phases are mainly a rewrite of Bastiaan Heeren's Top, using my own code conventions and ideals of simplicity. The most notable change being the use of Roman Cheplyaka's monad-classes (a little bit augmented): to handle the Monad stack building a Solver (instead of a homegrown machinery I could not understand well). At this point, only a bottom-up Collect, a no-op Order and a Greedy Solver are implemented, supporting: monomorphic types (Monotype), parametric polymorphism (Polytype), type class polymorphism (Class), and type synonyms (Synotype). The quite understandable thesis of Bastiaan Heeren explains a lot of this in details: Top Quality Type Error Messages.

The Attribute Grammar System of Universiteit Utrecht is used to demonstrate how to collect type constraints from an expression (Expr), and then how to transform this implicitely typed expression into an explicitely typed lol-calculus expression

See also: the helium compiler.

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