Hi!
Does this fold implementation try to do what in Smalltalk is usually
done using the inject:into: selector? An example for that would be:
{ 'a'. 'b'. 'c' . 'd' } inject: 'foo' into: [ :x :y | '(' + x + ',' +
y + ')' ]
would evaluate to: '(((foo,a), b), c), d)'
(or something similar, depending on whether you do a fold-right or
fold-left.
If this is the idea behind that patch, using Smalltalk or ObjC2 blocks
would probably give a more elegant solution...
Best regards,
Günther
On 13 Jun 2009, at 11:35, David Chisnall wrote:
> On 13 Jun 2009, at 09:15, Niels Grewe wrote:
>
>> Hi again,
>>
>> This really is fun! I never thought that implementing fold would be
>> that much
>> easier. I have attached a patch and sample code on which I would
>> like to
>> get some feedback. I know that there is quite some duplicated code
>> that
>> should be refactored into a more generic implementation for arbitrary
>> collections and HOM-variations. What else is there that could be done
>> to improve this?
>
> Good catch on the nil test in map.
>
> I don't really understand your code. What is the selfArgs array for?
> You seem to be trying to implement something like NSIndexSet, but I
> can't really work out why.
>
> Did you try running your test program? It references a variable
> 'lower' which doesn't exist, so it shouldn't even compile...
>
> 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
>
> To do this, you need to set arg 2 of the invocation to last value
> returned (initially to the original arg 2 value) and then invoke with
> the target set to the next element in the array (or the other way
> around, for folding the other way). This doesn't require any of the
> selfArgs-related stuff, so I don't see what it is trying to
> accomplish.
>
> David
>
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