name for a function that transforms assignment statements to expressions

Question

update

Since one effect of these functions is to provide a way to use method chaining on methods that would not normally support it *, I'm considering calling them chain and copychain, respectively. This seems less than ideal though, since the would-be copychain is arguably a more fundamental concept, at least in terms of functional programming.

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original

I'm calling it a boxer for now. The code is in Python, though the question is general:

def boxer(f):
    """Return a function g(o, *args, **keyargs) -> o

    `g` calls `f` on `o` with the remaining arguments
        and returns `o`.

    >>> l = [2]
    >>> def increment_list_element(l, i):
    ...     l[0] += i
    >>> adder = boxer(increment_list_element)
    >>> adder(l, 2)
    [4]
    >>> def multiply_list_element(l, i):
    ...     l[0] *= i
    >>> multiplier = boxer(multiply_list_element)
    >>> sum(multiplier(l, 6))
    24
    """
    def box(o, *args, **keyargs):
        f(o, *args, **keyargs)
        return o
    return box

A similar concept copies the would-be assignee, and assigns to and returns the copy. This one is a "shadow_boxer":

from copy import deepcopy

def shadow_boxer(f):
    """Return a function g(o, *args, **keyargs) -> p

    `g` deepcopies `o` as `p`,
        executes `f` on `p` with the remaining arguments,
        and returns `p`.

    >>> l = [2]
    >>> def increment_list_element(l, i):
    ...     l[0] += i
    >>> adder = shadow_boxer(increment_list_element)
    >>> adder(l, 2)
    [4]
    >>> def multiply_list_element(l, i):
    ...     l[0] *= i
    >>> multiplier = shadow_boxer(multiply_list_element)
    >>> sum(multiplier(l, 6))
    12
    """
    def shadow_box(o, *args, **keyargs):
        p = deepcopy(o)
        f(p, *args, **keyargs)
        return p
    return shadow_box

In addition, I'd like to find out about resources for learning more about these sorts of things — though I'm similarly unsure of a name for "these sorts of things". It does seem related to functional programming, although as I understand it, these technique would be unnecessary in a true functional language.

Answer 1

What the boxer function returns is probably defined closure in some programming languages. If there is not already a function with this name, I would call the function closure.

Answer 2

This is pretty much the same thing as Ruby's Object#tap. Don't know how you feel about the name, but that's what they call it.