[squeak-dev] Collection's #fold: vs #reduce:
Juan Vuletich
juan at jvuletich.org
Tue Nov 2 20:50:09 UTC 2010
Eliot Miranda wrote:
>
>
> On Tue, Nov 2, 2010 at 1:23 PM, Juan Vuletich <juan at jvuletich.org
> <mailto:juan at jvuletich.org>> wrote:
>
> Nicolas Cellier wrote:
>
>
> I'd say which selector are implemented in Pharo and Cuis ?
> We should better converge.
>
> Nicolas
>
>
>
> Hi folks,
>
> Cuis doesn't include any of them yet. I can add whatever people
> prefer. What I'd do different is the implementation:
>
> fold: aBinaryBlock
>
> "Evaluate the block with the first two elements of the receiver,
> then with the result of the first evaluation and the next element,
> and so on. Answer the result of the final evaluation. If the
> receiver
> is empty, raise an error. If the receiver has a single element,
> answer
> that element."
> "
> #('if' 'it' 'is' 'to' 'be' 'it' 'is' 'up' 'to' 'me') fold: [:a
> :b | a, ' ', b]
> "
> | noPreviousValue |
> noPreviousValue := Object new. "something that can't be in
> the receiver"
> ^self inject: noPreviousValue into: [ :previousValue :each |
> previousValue == noPreviousValue
> ifTrue: [ each ]
> ifFalse: [ aBinaryBlock value: previousValue value: each ]]
>
> This is easier to understand, and it also makes clear the relation
> between #fold: (or #reduce:) and #inject:into: .
>
>
> I disagree. inject:into: is not particularly easy to understand,
> whereas both the existing fold: and reduce: are understandable in
> terms of do:.
I say this is easier to understand, given that #inject:into: is already
understood. #inject:into: and #fold: / #reduce: are very close in what
they do. So close, that it is best to show how they differ. That's what
my implementation does. Showing the use of #inject:into: (with proper
names for block args) is a didactic bonus.
> Also the use of inject:into: isn't really buying you anything since
> the logic in the block within the inject:into: usage is as complex as
> that within fold: or reduce:. Further, this /is/ a lot slower because
> of the extra level of evaluation (there's an extra block activation
> around each element).
>
>
> best,
> Eliot
No, it is not slower:
[100000 timesRepeat: [#('if' 'it' 'is' 'to' 'be' 'it' 'is' 'up' 'to'
'me') fold: [:a :b | a, ' ', b]]] timeToRun 2710 | 879
[100000 timesRepeat: [#('if' 'it' 'is' 'to' 'be' 'it' 'is' 'up' 'to'
'me') foldx: [:a :b | a, ' ', b]]] timeToRun 2723 | 874
[100000 timesRepeat: [#('if' 'it' 'is' 'to' 'be' 'it' 'is' 'up' 'to'
'me') reduce: [:a :b | a, ' ', b]]] timeToRun 2780 | 881
#foldx: is my implementation. In all cases, the first number is regular
interpreter Squeak 4.2.4beta1U.app, the second number is Cog Squeak
5.8b10-1.app on a 1.6GHz Mac mini.
The argument about complexity is more aesthetic than anything. My
version doesn't need assignment to outer temps, and I see that 'cleaner'
and closer to FP.
Cheers,
Juan Vuletich
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