Data.Unamb

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 -> a

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] -> a

n-ary unamb

assuming :: Bool -> a -> a

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

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

The value of agreeing values (or undefined/bottom)

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

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 -> a

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 -> a

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

por :: Bool -> Bool -> Bool

Parallel or

pand :: Bool -> Bool -> Bool

Parallel and

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

Parallel min with minBound short-circuit

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

Parallel max with maxBound short-circuit

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

Parallel multiplication with 0 short-circuit

Some related imperative tools

amb :: a -> a -> IO a

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 a

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

Exception thrown if neither value evaluates

data BothBottom

Instances

Show BothBottom

Typeable BothBottom

Exception BothBottom