10.1 General

The module Value contains two general control procedures.

Wait

{Value.wait +X}

blocks until X is determined.

WaitOr

{Value.waitOr X Y}

blocks until at least one of X or Y is determined.

!!

{Value.'!!' X Y}

returns a future Y for X, i. e., a read-only placeholder for X.

byNeed

{Value.byNeed +P X}

creates a future X. When X is requested (i. e., some thread blocks on X), the unary procedure P is applied to a fresh variable Y in a new thread. When the application of P is fully reduced, the variable associated with X is bound to Y.