License	BSD-3-Clause
Safe Haskell	Safe-Inferred
Language	Haskell2010

Swarm.Language.Typecheck.Unify

Description

Utilities related to type unification.

Synopsis

data UnifyStatus
- = Apart
- | MightUnify
- | Equal
unifyCheck :: UType -> UType -> UnifyStatus

Documentation

data UnifyStatus Source #

The result of doing a unification check on two types.

Constructors

Apart	The two types are definitely not equal; they will never unify no matter how any unification variables get filled in. For example, (int * u0) and (u1 -> u2) are apart: the first is a product type and the second is a function type.
MightUnify	The two types might unify, depending on how unification variables get filled in, but we're not sure. For example, (int * u0) and (u1 * bool).
Equal	The two types are most definitely equal, and we don't need to bother generating a constraint to make them so. For example, (int * text) and (int * text).

Instances

Instances details

Monoid UnifyStatus Source #
Instance details Defined in Swarm.Language.Typecheck.Unify Methods mempty :: UnifyStatus # mappend :: UnifyStatus -> UnifyStatus -> UnifyStatus # mconcat :: [UnifyStatus] -> UnifyStatus #
Semigroup UnifyStatus Source #	The `Semigroup` instance for `UnifyStatus` is used to combine results for compound types.
Instance details Defined in Swarm.Language.Typecheck.Unify Methods (<>) :: UnifyStatus -> UnifyStatus -> UnifyStatus # sconcat :: NonEmpty UnifyStatus -> UnifyStatus # stimes :: Integral b => b -> UnifyStatus -> UnifyStatus #
Read UnifyStatus Source #
Instance details Defined in Swarm.Language.Typecheck.Unify Methods readsPrec :: Int -> ReadS UnifyStatus # readList :: ReadS [UnifyStatus] # readPrec :: ReadPrec UnifyStatus # readListPrec :: ReadPrec [UnifyStatus] #
Show UnifyStatus Source #
Instance details Defined in Swarm.Language.Typecheck.Unify Methods showsPrec :: Int -> UnifyStatus -> ShowS # show :: UnifyStatus -> String # showList :: [UnifyStatus] -> ShowS #
Eq UnifyStatus Source #
Instance details Defined in Swarm.Language.Typecheck.Unify Methods (==) :: UnifyStatus -> UnifyStatus -> Bool # (/=) :: UnifyStatus -> UnifyStatus -> Bool #
Ord UnifyStatus Source #
Instance details Defined in Swarm.Language.Typecheck.Unify Methods compare :: UnifyStatus -> UnifyStatus -> Ordering # (<) :: UnifyStatus -> UnifyStatus -> Bool # (<=) :: UnifyStatus -> UnifyStatus -> Bool # (>) :: UnifyStatus -> UnifyStatus -> Bool # (>=) :: UnifyStatus -> UnifyStatus -> Bool # max :: UnifyStatus -> UnifyStatus -> UnifyStatus # min :: UnifyStatus -> UnifyStatus -> UnifyStatus #

unifyCheck :: UType -> UType -> UnifyStatus Source #

Given two types, try hard to prove either that (1) they are Apart, i.e. cannot possibly unify, or (2) they are definitely Equal. In case (1), we can generate a much better error message at the instant the two types come together than we could if we threw a constraint into the unifier. In case (2), we don't have to bother with generating a trivial constraint. If we don't know for sure whether they will unify, return MightUnify.