null
-- generate the void object of
type DOM_NULL
null(
)
returns the void object of domain
type DOM_NULL
.
null()
the void object of domain type DOM_NULL
.
null(
)
returns the only object of domain
type DOM_NULL
. It
represents an empty sequence of MuPAD expressions or
statements.print
or reset
return the void object.null
is a function of the system kernel.null(
)
returns the void object
which does not produce any screen output:
>> null()
The resulting object is of domain type DOM_NULL
:
>> domtype(null())
DOM_NULL
This object represents the empty expression sequence and the empty statement sequence:
>> domtype(_exprseq()), domtype(_stmtseq())
DOM_NULL, DOM_NULL
Some system functions such as print
return the void object:
>> print("Hello world!"):
"Hello world!"
>> domtype(%)
DOM_NULL
The void object is removed from lists, sets, and expression sequences:
>> [null(), a, b, null(), c], {null(), a, b, null(), c}, f(null(), a, b, null(), c)
[a, b, c], {a, b, c}, f(a, b, c)
>> a + null() + b = _plus(a, null(), b)
a + b = a + b
>> subsop([a, x, b], 2 = null()), subs({a, x, b}, x = null())
[a, b], {a, b}
However, null(
)
is a valid
entry in arrays and tables:
>> a := array(1..2): a[1] := 1: a[2] := null(): a
+- -+ | 1, null() | +- -+
>> domtype(a[1]), domtype(a[2])
DOM_INT, DOM_NULL
>> t := table(null() = "void", 1 = 2.5, b = null())
table( b = null(), 1 = 2.5, null() = "void" )
>> domtype(t[b]), t[]
DOM_NULL, "void"
>> delete a, t:
The void object remains if you delete all elements from an expression sequence:
>> a := (1, b): delete a[1]: delete a[1]: domtype(a)
DOM_NULL
The operand function op
returns the void object when applied
to an object with no operands:
>> domtype(op([])), domtype(op({})), domtype(op(f()))
DOM_NULL, DOM_NULL, DOM_NULL
>> delete a: