Re: APL-style array indexing in Kawa - a sketch

[Per Bothner <per at bothner dot com>]

On 08/17/2015 08:37 PM, Jamison Hope wrote:
> On Aug 17, 2015, at 6:47 PM, Per Bothner <per@bothner.com> wrote:
>
> > We could define [<:] as a supported syntax (see $bracket-list$ in syntax.scm).
> > It would be relative easy to define 0 as the default lower bound, but that
> > doesn't quite do what you want.  We could define [<;] as a special magic value
> > that gets coerced to a specific range depending on context.
>
> Hmm can we pick something that won't confuse paredit mode?

I'm not familiar with paredit - but why would [<:] confuse it?

> (array-map (lambda (x) (* 2 x)) ARR) => a new array where each element
> is doubled in value.
>
> (array-map + ARR1 ARR2) => a new array representing the elementwise sum
> of the elements of ARR1 and ARR2.
>
> (I'm imagining that the array-map call wouldn't allocate a new data
> buffer, but would just close over the supplied function and array(s),
> lazily applying the function to array elements as needed.)

"Lazily" is confusing here.  I think array-map should eager, in the
same way vector-map is.  What it should do:
(1) Figure out the shape of the result.  (The same as the argument, if
a single argument; otherwise they may be "broadcast" in the Racket sense.)
(2) Allocate an Object[] buffer for the result whose length is the
element-count of the shape.
(3) Iterate of the shape (which is the same as iterating over the buffer);
extract the corresponding argument array value using the same (or broadcast)
indexes; call the function.

http://docs.racket-lang.org/math/array_pointwise.html

The Racket array functions is another place to look for inspiration.
--
	--Per Bothner
per@bothner.com   http://per.bothner.com/