Create a potentially-parallel computation, and return a future (or promise) that can be used to query the result of the forked computataion.

  spawn p = do
    r <- new
    fork (p >>= put r)
    return r

Like spawn, but the result is only head-strict, not fully-strict.

Wait for the result of a future, and then return it.

Spawn a pure (rather than monadic) computation. Fully-strict.

  spawnP = spawn . return

Forks a computation to happen in parallel. The forked computation may exchange values with other computations using IVars.

creates a new IVar

put a value into a IVar. Multiple puts to the same IVar are not allowed, and result in a runtime error.

put fully evaluates its argument, which therefore must be an instance of NFData. The idea is that this forces the work to happen when we expect it, rather than being passed to the consumer of the IVar and performed later, which often results in less parallelism than expected.

Sometimes partial strictness is more appropriate: see put_.

like put, but only head-strict rather than fully-strict.

creates a new IVar that contains a value

creates a new IVar that contains a value (head-strict only)