unamb-0.2: Unambiguous choice





Unambiguous choice

For non-flat types (where values may be partially defined, rather than necessarily bottom or fully defined) and information merging, see the lub package, http://haskell.org/haskellwiki/Lub.


Purely functional unambiguous choice

unamb :: a -> a -> aSource

Unambiguous choice operator. Equivalent to the ambiguous choice operator, but with arguments restricted to be equal where not bottom, so that the choice doesn't matter. See also amb.

If anything kills unamb while it is evaluating (like nested unambs), it can be retried later but, unlike most functions, work may be lost.

Some useful special applications of unamb

unambs :: [a] -> aSource

n-ary unamb

assuming :: Bool -> a -> aSource

Yield a value if a condition is true. Otherwise undefined.

asAgree :: Eq a => a -> a -> aSource

The value of agreeing values (or undefined/bottom)

parCommute :: (a -> a -> b) -> a -> a -> bSource

Turn a binary commutative operation into that tries both orders in parallel. Useful when there are special cases that don't require evaluating both arguments. For non-flat types and information merging, see parCommute in the lub package.

parIdentity :: Eq a => (a -> a -> a) -> a -> a -> a -> aSource

Binary operation with left & right identity element. For instance, (*) & 1, (&&) & True, (||) & False, min & maxBound, max & minBound. Tests either argument as identity, in parallel.

parAnnihilator :: Eq a => (a -> a -> a) -> a -> a -> a -> aSource

Binary operation with annihilator element. For instance, (*) & 0, (&&) & False, (||) & True, min & minBound, max & maxBound. Tests either argument as annihilator, in parallel.

por :: Bool -> Bool -> BoolSource

Parallel or

pand :: Bool -> Bool -> BoolSource

Parallel and

pmin :: (Ord a, Bounded a) => a -> a -> aSource

Parallel min with minBound short-circuit

pmax :: (Ord a, Bounded a) => a -> a -> aSource

Parallel max with maxBound short-circuit

pmult :: Num a => a -> a -> aSource

Parallel multiplication with 0 short-circuit

Some related imperative tools

amb :: a -> a -> IO aSource

Ambiguous choice operator. Yield either value. Evaluates in separate threads and picks whichever finishes first. See also unamb and race.

race :: IO a -> IO a -> IO aSource

Race two actions against each other in separate threads, and pick whichever finishes first. See also amb.

Exception thrown if neither value evaluates