[fpc-devel] for-in-index loop

[Alexander Klenin]

On Sat, Jan 26, 2013 at 7:10 AM, Mark Morgan Lloyd
<markMLl.fpc-devel at telemetry.co.uk> wrote:
> However, I'd suggest that there are two possible category of extension:
> those that implement a clearly-delimited first-class object with interesting
> properties, and those that don't.
>
> Something like a <generic>, or a /regular expression/ (borrowing from Perl),
> or a [list of elements] fall into the first category, and should be
> comparatively easy to add to a language- and for a user to ignore if he
> doesn't like them.
I disagree with the statement that generics are easy to add.
I disagree with a statement that adding Perl's first-class regexp
syntax is a good idea at all --
talk about messy parsing :)
I agree that [list of elements] is a good feature, but it is already present.
So, unfortunately, I can not accept your list as an example of "good"
extensions.

> Something like
>>>>>    for v in a index i do
> falls squarely into the latter category: it's messy to parse, worse to read,
I disagree with the statement that "for-in-index" loop is "messy to parse".
You can look at the code provided by Vasily: there is no problem in
parsing at all.
The question of readabllity is indeed subjective, and I am quite open
for altervative proposals here.
The current syntax was chosen based on the requirements to avoid new
keywords and traditional
Pascal preference for keywords over punctuation.
However, I may consider variants below (v = value, i = index, a = array):
for v, i in a do
for i, v in a do // most similar to Python
for (v, i) in a do
for v[i] in a do
for v index i in a do // perhaps this is really better -- I am not sure
for index i in a do // we may allow to omit the value and loop only
over the index -- this could be useful for STL sets
for v key i in a do // new keyword = bad

> and is completely unlike any existing language idioms.
Do you mean idioms existing in Pascal, or general language idioms?

--
Alexander S. Klenin