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isnull(arg1 [, arg2, ...])

Keywords: macros, general, variables, null variables
isnull(arg) returns T if arg has type NULL and false otherwise.

isnull(arg1, arg2, ..., argk) returns a LOGICAL vector, each element of
which is True or False depending on whether or not the corresponding
argument is NULL.

See topic 'NULL' for information on NULL variables.

The principal use of isnull() is in checking the arguments of a macro
for appropriateness.

  Cmd> isnull(NULL, sqrt(2)) # returns vector(T, F)

See also topics 'macros', isarray(), ischar(), isdefined(), isfactor(),
isfunction(), isgraph(), islogic(), ismacro(), ismatrix(), isname(),
isnumber(), isreal(), isscalar(), isstruc(), isvector().

Gary Oehlert 2003-01-15