3.2 Variable Status

The following procedures allow to inspect a variable's status.

IsFree

{Value.isFree X ?B}

tests whether X is currently free.

IsDet

{Value.isDet X ?B}

tests whether X is determined.

IsFuture

{Value.isFuture X ?B}

tests whether X is a future.

IsFailed

{Value.isFailed X ?B}

tests whether X is a failed value.

IsKinded

{Value.isKinded X ?B}

tests whether X is currently kinded, i. e., is constrained but not yet determined. For example, foo(a:12 ...) is kinded because it is constrained to be a record, yet its arity is not yet known. Also, a non-determined finite domain variable is kinded: its type is known to be integer, but its value is not yet determined. Similarly for finite set variables.

status

{Value.status X ?T}

returns status and type information on X. If X is free, the atom free is returned. If X is a future, the atom future is returned. If X is a failed value, the atom failed is returned. If X is kinded, the tuple kinded(Y) is returned, where Y is bound to either the atoms int, fset or record, depending on the type of X. If X is determined, the tuple det(Y) is returned, where Y is bound to the atom as returned by {Value.type X}.

type

{Value.type +X ?A}

returns an atom describing the type of X. If X is of one of the standard primary types depicted in Figure 2.1 (except ``value''), then A is constrained to the most specific of int, float, record, tuple, atom, name, procedure, cell, byteString, bitString, chunk, array, dictionary, bitArray, 'class', object, 'lock', port, space, or 'thread'. If any other atom is returned, this means that X is of no standard primary type, but an implementation-dependent extension.