On Sat, Jun 13, 2009 at 10:35:44AM +0100, David Chisnall wrote:
> Good catch on the nil test in map.
Right, I somehow forgot to mention that in the email.
> Did you try running your test program? It references a variable
> 'lower' which doesn't exist, so it shouldn't even compile...
My bad. I manually changed variable names before attaching the code.
"lower" should always be "input": %s/lower/input/g
> I expect to use a fold method like this:
>
> id input = A(@"a", @"b", @"c");
> [ETTranscript show: [[input fold] stringByAppendingString: @"letters:
> "]];
>
> I would then get the output:
>
> letters: abc
I personally find that counter-intuitive. The selector you pass to the
proxy object seems represent a folding function, which should take
as arguments the accumulator and an element of the collection to operate
upon (at least). You seem to take @"letters: " as the initial
value of the accumulator. I'd then figure that the receiver will be
element to operate on. So on casual reading the code seems to say
'fold input by appending @"letters: " to each element', which is not
what you want.
Of course, intuitions vary wildly among people, so feel free to
disagree.
But you got another point here: I totally disregarded that one might
want to set the initial value of the accummulator. (It's not my usual
usage pattern, I usally set those to something irrelevant). So what
about writing the above like this:
[[input fold: @"letters: "] stringByAppendingString: (NSString*)input];
Reusing the input array signifies that you want to use the elements of
the input array at that position of the method. I'm using that
mysterious (and clumsy, I admit it) selfArgs array to determine the
positions at which to replace the reference to the whole array with a
reference to the element in question.
As an additional benefit you can then use more complex methods as
folding functions. Suppose NSString implemented
-stringByAppendingString:andString:, you could easily do stuff like
this:
[[input fold: @"letters: "] stringByAppendingString: @"-"
andString:(NSString*)input];
Wich produces the result "letters: -a-b-c" [0] and would, as far as i
can see, not feasible with the implementation you are suggesting. This
approach is still a little bit arkward since if you really want to use
the input array as an argument to the method you're folding with then
you'd need to copy it.
Additionally, I was going to reply to Günther's enquiry about blocks
that I chose not to use them since they require clang, but since you're
just proposing to switch to clang as the default compiler for Étoilé,
implementing this whole higher order messaging stuff with blocks would
probably be okay, wouldn't it?
regards
Niels
--
[0] Or better: Should produce. There is a bug in what I sent yesterday
that prevented this from working.
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