From APL

[Simen Kjaeraas]

On Thu, 20 Sep 2012 13:55:48 +0200, bearophile <bearophileHUGS at lycos.com>  
wrote:

> Section 2.3 is about Scan operations, that are like reduce or fold, but  
> keep all the intermediate results too:
>
> +\ of 3 1 2 4
>
> is 3 4 6 10
>
> Some lazy scans are present in the Haskell Prelude too (and in  
> Mathematica) (the Prelude contains functions and constants that are  
> loaded on default):
> http://zvon.org/other/haskell/Outputprelude/scanl_f.html
>
> I think scans are not present in Phobos. Maybe one or two are worth  
> adding.

See attached. Mayhaps I should post this as a pull request?


> ------------------
>
> Section 2.5 suggests to generalize the dot product:
>
>> If the + and * of the Fortran 77 DO loops for inner product are  
>> replaced by other functions, a whole family of interesting inner  
>> products appear,<
>
> Some examples of usage (in J language):
>
> Associative search                   *./..=y
> Inverted associative                 x+./..~:y
> Minima of residues for primes        x<./..|y
> Transitive closure step on Booleans  y+./..*.y
> Minima of maxima                     x<./..>.y
>
> Maybe a higher order function named "dot" (that takes two callables) is  
> worth adding to Phobos. But I am not sure.

So that's basically mapReduce, right? We've got that, just not as succinct.


-- 
Simen
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