Data.LVar.Internal.Pure

This is not a datatype for the end-user.

Rather, this module is for building new LVar types in a comparatively easy way: by putting a pure value in a mutable container, and defining a put operation as a pure function.

The data structure implementor who uses this module must guarantee that their put operation computes a least upper bound, ensuring that the set of states that their LVar type can take on form a join-semilattice (http://en.wikipedia.org/wiki/Semilattice).

Documentation

newtype PureLVar s t

An LVar which consists merely of an immutable, pure value inside a mutable box.

Constructors

PureLVar (LVar s (IORef t) t)

Instances

Eq (PureLVar s v)

Physical identity, just as with IORefs.

Show a => Show (PureLVar Frzn a)

DeepFrz a => DeepFrz (PureLVar s a)

type FrzType (PureLVar s a) = PureLVar Frzn (FrzType a)

newPureLVar :: JoinSemiLattice t => t -> Par d s (PureLVar s t)

A new pure LVar populated with the provided initial state.

putPureLVar :: JoinSemiLattice t => PureLVar s t -> t -> Par d s ()

Put a new value which will be joined with the old.

waitPureLVar :: (JoinSemiLattice t, Eq t) => PureLVar s t -> t -> Par d s ()

Wait until the pure LVar has crossed a threshold and then unblock. (In the semantics, this is a singleton query set.)

freezePureLVar :: PureLVar s t -> Par QuasiDet s t

Freeze the pure LVar, returning its exact value. Subsequent puts will raise an error.

fromPureLVar :: PureLVar Frzn t -> t

Read the exact contents of an already frozen PureLVar.

getPureLVar :: (JoinSemiLattice t, Eq t) => PureLVar s t -> [t] -> Par d s t

Blocks until the contents of lv are at or above one element of thrshSet, then returns that one element.

unsafeGetPureLVar :: (JoinSemiLattice t, Eq t) => PureLVar s t -> (t -> Bool) -> Par d s t

Like getPureLVar but uses a threshold function rather than an explicit set.

Verifying lattice structure

verifyFiniteJoin :: (Eq a, Show a) => [a] -> (a -> a -> a) -> Maybe String

Takes a finite set of states and a join operation (e.g., for an instance of JoinSemiLattice) and returns an error message if the join-semilattice properties don't hold.

verifyFiniteGet :: (Eq a, Show a, JoinSemiLattice a, Eq b, Show b) => [a] -> (b, b) -> (a -> b) -> Maybe String

Verify that a blocking get is monotone in just the right way. This takes a designated bottom and top element.