Language.PureScript.TypeChecker.Unify

Functions and instances relating to unification

Documentation

freshType :: MonadState CheckState m => m Type

Generate a fresh type variable

solveType :: (MonadError MultipleErrors m, MonadState CheckState m) => Int -> Type -> m ()

Update the substitution to solve a type constraint

substituteType :: Substitution -> Type -> Type

Apply a substitution to a type

unknownsInType :: Type -> [Int]

Compute a list of all unknowns appearing in a type

unifyTypes :: (MonadError MultipleErrors m, MonadState CheckState m) => Type -> Type -> m ()

Unify two types, updating the current substitution

unifyRows :: forall m. (MonadError MultipleErrors m, MonadState CheckState m) => Type -> Type -> m ()

Unify two rows, updating the current substitution

Common labels are identified and unified. Remaining labels and types are unified with a trailing row unification variable, if appropriate.

alignRowsWith :: (Type -> Type -> a) -> Type -> Type -> ([a], (([(Label, Type)], Type), ([(Label, Type)], Type)))

Align two rows of types, splitting them into three parts:

• Those types which appear in both rows
• Those which appear only on the left
• Those which appear only on the right

Note: importantly, we preserve the order of the types with a given label.

replaceVarWithUnknown :: MonadState CheckState m => Text -> Type -> m Type

Replace a single type variable with a new unification variable

replaceTypeWildcards :: (MonadWriter MultipleErrors m, MonadState CheckState m) => Type -> m Type

Replace type wildcards with unknowns

varIfUnknown :: Type -> Type

Replace outermost unsolved unification variables with named type variables