Internal operands of a domain element

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extop(object, i)
extop(object, i .. j)


extop(object) returns all operands of the domain element object.

extop(object, i) returns the i-th operand.

extop(object, i..j) returns the i-th to j-th operand.

For objects of a basic data type such as expressions, sets, lists, tables, arrays, hfarrays etc., extop yields the same operands as the function op. See the corresponding documentation for details on operands. The main difference to the function op is that extop cannot be overloaded. Therefore, it guarantees direct access to the operands of the internal representation of elements of a library domain. Typically, extop is used in the implementation of the "op" method of a library domain that overloads the system's op function.

A domain element consists of a reference to the corresponding domain and a sequence of values representing its contents. The function extop allows access to the domain and the operands of this internal data sequence.

extop(object) returns a sequence of all internal operands except the 0-th one. This call is equivalent to extop(object, 1..extnops(object)).

extop(object, i) returns the i-th internal operand. In particular, the domain of the object is returned by extop(object, 0) if object is an element of a library domain. If object is an element of a kernel domain, the call extop(object, 0) is equivalent to op(object, 0).

extop(object, i..j) returns the i-th to j-th internal operands of object as an expression sequence; i and j must be nonnegative integers with i smaller or equal to j. This sequence is equivalent to extop(object, k) $k = i..j.

extop returns FAIL if a specified operand does not exist. Cf. Example 4.

The operands of an expression sequence are its elements. Note that such sequences are not flattened by extop.


Example 1

We create a new domain d and use the function new to create an element of this type. Its internal data representation is the sequence of arguments passed to new:

d := newDomain("demo"): e := new(d, 1, 2, 3): extop(e)

Individual operands can be selected:

extop(e, 2)

Ranges of operands can be selected:

extop(e, 1..2)

The 0-th operand of a domain element is its domain:

extop(e, 0)

delete d, e:

Example 2

First, a new domain d is defined via newDomain. The "new" method serves for creating elements of this type. The internal representation of the domain is a sequence of all arguments of this "new" method:

d := newDomain("d"): d::new := () -> new(dom, args()):

The system's op function is overloaded by the following "op" method of this domain. It is to return the elements of a sorted copy of the internal data sequence. In the implementation of the "op" method, the function extop is used to access the internal data:

d::op := proc(x, i = null())
         local internalData;
         begin internalData := extop(x);
               op(sort([internalData]), i)

Due to this overloading, op returns different operands than extop:

e := d(3, 7, 1): op(e); extop(e)

delete d, e:

Example 3

For kernel data types such as sets, lists etc., extop always returns the same operands as op:

extop([a, b, c]) = op([a, b, c])

Expressions are of kernel data type DOM_EXPR, thus extop(sin(x), 0) is equivalent to op(sin(x), 0):

domtype(sin(x)), extop(sin(x), 0) = op(sin(x), 0)

Expression sequences are not flattened:

extop((1, 2, 3), 0), extop((1, 2, 3))

Example 4

Non-existing operands are returned as FAIL:

extop([1, 2], 4),  extop([1, 2], 1..4)



An arbitrary MuPAD® object

i, j

Nonnegative integers

Return Values

sequence of operands or the specified operand. FAIL is returned if no corresponding operand exists.

See Also

MuPAD Domains

MuPAD Functions