On Tuesday, June 3, 2014 10:36:37 AM UTC+5:30, Deb Wyatt wrote:
> That was just the first question. What does immutable really mean
> if you can add items to a list? and concatenate strings? I don't
> understand enough to even ask a comprehensible question, I guess.
It is with some pleasure that I see this question: Most people who are
clueless have no clue that they are clueless -- also called the
Be assured that this question is much harder and problematic than people
There are earlier discussions on this on this list, eg
[Sorry the archive thread is too broken to quote meaningfully]
Here's a short(!) summary:
Programmer's live in 2 worlds.
1. A timeless mathematical world. Philosophers call this the platonic world
after Plato's allegory of the cave:
2. An in-time world that is called "Empirical" in philosophy
You cannot reject 2 because your programs run in time and produce
effects (hopefully!) in the empirical world.
You cannot reject 1 because the time at which you - the programmer -
function is in another space-time from the run-time of your program.
The very fact that you write a program means you have (been able to)
algorithmize out a complex *process* into a simpler recipe - a *program*.
Once you see the need for both worldviews 1 and 2 you will see why even the most
deft=footed trip up doing this dance. eg. When someone says:
3 is immutable but [1,2,3] is mutable this is not a necessary fact but
an incidental choice of python's semantics.
Functional languages make everything immutable
Assembly language makes everything mutable -- you can self-modify the
code containing 3 as an immediate operand in an instruction into one containing
However the basic (necessary not incidental) fact remains - you need to dance
the two worldviews:
- platonic and empiric (in traditional philosophy lingo)
- declarative and imperative (in computer theory lingo)
- FP and OO styles (the two major fashions in programming languages)
Choose absolutely only the first and your program can have no effect
whatever including writing a result to the screen
Choose absolutely only the second that you can have no comprehension of your
You can find this further elaborated on my blog whose title is a summarization
of what Ive written above: http://blog.languager.org/search/label/FP
¹Heck! Steven showed some trick to make it happen in python also
But Ive not fathomed the black magic!