copyClosure

Copies the lexical closure of a procedure

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Syntax

copyClosure(f)

Description

copyClosure(f) copies the lexical closure of a procedure or procedure environment f.

Usually, when a procedure is copied, for example by assigning it to an identifier, the lexical closure of the procedure is not copied. Via the copied procedure one can change the lexical closure of the original procedure. Thus, the lexical closure of a procedure shows the so-called reference effect.

copyClosure may be used to copy the lexical closure of a procedure. Changes in the closure of the copy no longer affect the original procedure's closure.

Closures are implemented by procedure environments (kernel type DOM_PROC_ENV) in MuPAD^®. copyClosure works by copying all lexically enclosing procedure environments of a procedure.

copyClosure may also be used to copy a procedure environment and all its lexically enclosing environments only.

Examples

Example 1

Procedure closures show the reference effect: The procedure f generated by gen changes its closure via the variable i. A “normal” copy g of f changes the variable in the same closure, as is seen by repeatedly calling f versus g.

gen:= proc()
    option escape;
    local i;
begin
    i := 0;
    proc() begin i := i+1 end
end:

f := gen():
g := f:
f(), g(), f(), g()

If one now generates f again by calling gen, but copies g by calling copyClosure, then g has its own closure and now longer changes the variable i in the closure of f.

f := gen():
g := copyClosure(f):
f(), g(), f(), g()

Parameters

f	A procedure or procedure environment to be copied

Return Values

Copied procedure or procedure environment