Call by binding [was Re: [Tutor] beginning to code]

[Marko Rauhamaa]

Antoon Pardon <antoon.pardon at rece.vub.ac.be>:

> Op 25-09-17 om 11:41 schreef Marko Rauhamaa:
>> Antoon Pardon <antoon.pardon at vub.be>:
>>
>>> the semantics of an assignment depends on the language
>> I've only seen one kind of assignment in the general-purpose
>> programming languages I know, maybe with the exception of Prolog and
>> Rust.
>
> I disagree. In languages like Pascal an asignment mutates the target
> that the left hand refers to, by copying over the value from the right
> side. In languages like python an asignment lets the target refer to a
> new entity.

In Python, assignment "mutates the target" as well. It's only that in
Python, the target is always a pointer.

Here's proof (up to isomorphism):

   >>> x = object()
   >>> y = object()
   >>> id(x)
   139719622467712
   >>> x = y
   >>> id(x)
   139719622467728


Meaning. Before:

   +---------- x ----------+
   |    139719622467712    |
   +-----------------------+

After:

   +---------- x ----------+
   |    139719622467728    |
   +-----------------------+

So we can see the contents of x have been mutated.


Marko