[REBOL] Re: syntax across languages
From: joel:neely:fedex at: 6-Nov-2003 7:20
Hi, Maarten, and all,
There's a serious question at the end of all the yammering below! ;-)
Maarten Koopmans wrote:
>>came accross an interesting site on "syntax across languages"
>>which is soliciting help with constructs in various languages
>>including rebol.
>>They are currently missing 120 syntax constructs for rebol.
>
> Most of them are available in REBOL but not in the comparison. If I only
> had time...
>
I can relate!
On the other hand, I'm also ambivalent their terminology; the table of
contents maintains the "syntax" pretense, but there are really three
different levels being addressed (somewhat indiscriminantly):
1 lexical rules (e.g. structure of a user-defined name/word)
2 higher-order syntax (e.g. structure of an "if" statement)
3 language features (e.g. "get type/class [of] object/instance/value")
I'd be glad to be updated, but I haven't seen (1) fully documented
anywhere for REBOL. (Remember recent -- and not so recent -- posts
about what characters are allowed in a word? IIRC most such questions
get resolved by trial and error or advice from someone who's already
traveled that road, not by pointing to section x.y in the manual.)
As for (2), it doesn't exists! I'm not trying to be pedantic here,
but sincerely believe that one of the early steps to "getting" REBOL
is to realize that e.g. THERE IS NO "IF" STATEMENT, but merely some
functions (IF, IF/ELSE, EITHER) that take an argument of type
[LOGIC! NONE!] and one or two arguments of type [BLOCK!] and, if you
so choose, YOU CAN WRITE YOUR OWN.
Being pragmatic, I know that a short answer to the question: "How
can I say the likely equivalent of
if (buff [0] == '\0') {
p--;
} else {
p = q % ++r;
}
is
either zero? length? buff [
p: p - 1
][
p: q // r: r + 1
]
but that doesn't necessarily help the questioner make the leap to
p: either zero? length? buff [
p - 1
][
q // r: r + 1
]
or even more REBOL-ish reconceptualizations of the programming task.
That brings me to (3), where IMHO it becomes most clear that efforts
such as the page in question often become either too encylpaedic for
ease of use, or else too superficial for useful ... use. It's one
thing to take two languages that share most of their conceptual base
(e.g. Pascal and C, ALGOL and Pascal, etc.) and address in a fairly
complete way the questionS (plural emphasized):
- What are the correspondences between the languages (i.e. for those
features that are conceptually similar, how does one "respell"
from one notation to the other)? In this category, explaining that
Pascal uses "begin ... end" for sequences of statements, while C
uses "{ ... }" is reasonable.
- What are points of NON-CORRESPONDENCE between the languages, and what
effect does that have on one's programming/design thinking? In this
category, the nesting of lexical scope (e.g. procedures defined
locally to enclosing procedures in Pascal, vs. the flatter, assembly-
like model of C) can cause one to think and design quite differently.
I should also add that many of the issues under the second point above
often become significant when [only when?] designing programs that deal
with larger-than-toy problems.
But when approaching languages with substantially different conceptual
models, the second issue becomes so dominant that the first issue is
either irrelevant or misleading IMHO. For example, what is the REBOL
equivalent for the elementary PROLOG idiom
conc( [], L, L ).
conc( [X | L1], L2, [X | L3] ) :- conc( L1, L2, L3 ).
??? As much as we might like to write
conc: 'join
that just won't cut it, when trying to understand why
last( Item, List ) :- conc( _, [Item], List ).
works.
Inspired by discussions on this list, I started putting together some
recipes for a Perl-to-REBOL cookbook. I say "started" because I was
smacked in the face by the above issues on the very first recipe, which
dealt with the Perl substr function. You see, in Perl, substr can be
used both as an lvalue and an rvalue (a distinction which doesn't exist
in REBOL).
And OBTW, using an rvalue string expression as an rvalue in
Perl implicitly copies, while an lvalue string expression mutates...
And OBTW, the Perl splice function (more or less) does for
arrays what substr does for strings, but REBOL blocks are the closest
analog to arrays, and block! and string! types are both subsumed in the
REBOL meta-type series! so instead of defining SUBSTR, shouldn't one
actually define SUBSER and ...
So instead of a one-page recipe, I suddenly had a very long chapter (I
know you can't believe that I found lots to say on such a narrow topic
;-) and began to question whether anyone would bother to read it! On
the other hand, I don't want to spend the effort to produce something
that ends up being so superficial that it's a read-once-and-throw-away
(as is the case with too many books and articles in the computing
field IMHO).
So, here's my question (or two... sorry! ;-)
Does the attempt to provide a Berlitz-phrase-book mapping across really
different languages do more harm than good, or is it a reasonable foot
in the door for beginners?
Would a (for example) Perl-to-REBOL cookbook be of enough value to
justify the (substantial) effort to produce it with reasonable quality
and completeness, and would there be a large enough market for such a
thing to have reasonable ROI? Where could I place the balance between
simplicity/brevity versus honesty/completeness to maximize the value?
With only a hint toward to the recent thread started by Petr, I have
to admit that there are many more things about REBOL to play with than
I have time for, there are many more ways to (try to) help REBOL grow
than I can fit in, and REBOL is only a small part of my life agenda
(with many work obligations and other responsibilities/commitments).
I have to work hard at budgeting my increasingly tight discretionary
time to those areas that have the greatest value (in multiple senses
of the word).
Any/all feedback/comments are welcome!
-jn-
