indexing

[eddier]

I absolutely LOVE the implicit  indexing Lutz. Just one question, can we do something with rest in a similar manar?



Eddie

[Lutz]

I love it just as much :), you could see implicit indexing as a natural extension of traditional LISP/Scheme evaluation:



traditional LISP

-----------------

built-ins -> apply to args

lambda -> apply to args



newLISP adds

---------------

contexts -> apply default function on args

lists -> indexing with args



Theoretically you could extend this to any data type, i.e. numbers:



number -> slice list in args



(1 '(a b c d e f g)) => (b c d e f g)  ; like (rest ...)

(2 '(a b c d e f g)) => (c d e f g)     ; like (rest (rest ...))

(2 '(a b c d e f g) 3) => (c d e)       ; like (slice ...)



have to think about this a little bit more ...



Lutz

[eddier]

Would something like

Code Select Expand


(0 3 '(a b c d e)) => (a b c d)
(1 2 '(a b c d e)) => (b c)


?



Eddie

[eddier]

Opps, I didn't see the slice up there. Wouldn't the semantics indicate

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(2 '(a b c d e f g) 3) =>
('(c d e f g) 3) =>
f

?

[Lutz]

I think the implicit nrest is fine:

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(1 '(a b c d)) => (b c d)
(2 '(a b c d)) => (c d)
(10 '(a b c d)) => ()

But I am not happy with the slice (idx theList len) or (idx len theList), just doesn't feel right, but the second syntax may be the better one.



I implemented (undocumented, experimental, list only, no strings) the implicit nrest in the new development version 8.4.7 here: http://newlisp.org/downloads/development">http://newlisp.org/downloads/development



Lutz

[eddier]

I was thinking more

Code Select Expand


(idx1 idx2 list)

(2 4 '(a b c d e f g)) => '(c d e)


But I'm not sure. The only thing that might be confusing is the position of the number. I still get confused on set-nth and nth-set. There might be a similar problem with implicit indexing and slicing.



Eddie

[Lutz]

Already did similar over the weekend, but length instead of idx2 this:

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(offset len lst)

(2 4 '(a b c d e f g)) => (c d e f)

so its's basically a slice with implicit indexing, and it also works with negative offsets:

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(-4 2 '(a b c d e f g)) => (d e)

and I also have the implicit index/rest now for negative index:

Code Select Expand


(-3 '(a b c d e f g)) => (e f g)

and everything works on strings too.



Lutz