On 27/11/2015 01:09, Steven D'Aprano wrote:
On Thu, 26 Nov 2015 12:23 pm, BartC wrote:
[First-class functions]
The names are declared, but the names are rarely bound to anything else.
Functions are just called the same boring way they are in C.
/They might as well be static definitions/.
Sure. And that's probably true for, oh, I don't know, I'll be generous, and
say that 95% of Python functions in use are of a straight-forward
pseudo-static form, using no dynamic features.
But it's the other 5% -- one in twenty -- that *shine*. They're the ones
that do things that you can't do in Pascal or C except with the greatest of
difficulty.
OK, you're worried about that 5%, I'm more concerned about the other 95%.
I'm not saying you shouldn't have dynamic functions at all, just that
it's not necessary for 100% to be dynamic.
I understand now that they are dynamic because that is the only
mechanism that Python has to create any function definition, even the
boring, static ones.
Together with the ability to subsequently re-bind the function name to
something else, that's a bit unfortunate because it makes it harder to
identifier calls to those functions in order to streamline them, or even
for someone to look at a bit of code and be sure whether that fn(a,b,c)
is calling the function defined as 'fn' a few hundred lines earlier or
something else entirely.
(MRAB mentioned Postscript, which also introduces functions using
executable statements.
However, Postscript was designed to execute code on-the-fly being
received a character at a time over a printer cable. It had a good excuse!)
Because Pascal doesn't have first-class functions, you couldn't pass a
function as an argument to another function. So the ODE solvers used a
hard-coded function as the equation to be solved. So if you wanted to solve
a particular equation, you had to *edit the source code of the program*,
modifying that hard-coded function to match your equation, then re-compile,
and then run the code. You couldn't just type in the equation you wanted to
solve and run the code.
Wouldn't Python have the same problem? If the equation to be solved, or
even the actual function to be executed, is input by the user, then
doesn't that require whichever one of exec() or eval() it is that
processes the source code?
There's a lot to like about Pascal,
It was designed for teaching. The original language would have needed
tweaking for use in general purpose programming.
but gosh it sure is lacking in power. C
at least has function pointers, which is a step up from Pascal, but still
pretty weak and feeble. If functions are first class values in Python,
Ruby, Lisp and others, they're second class values in C and third class in
Pascal.
I think they are more first class in Lisp than they are in most other
languages including Python. That doesn't stop Python still being jolly
useful though...
--
Bartc
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