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1 point by cchooper 5895 days ago | link | parent

Alternatively, it could be used to do an assoc lookup, which would make alists more like hashes.

  (= x '((a 1) (b 2) (c 3)))

  x!b
  => 2
Note that it returns the value not the pair, as with hashes. It's not as powerful as assoc but more convenient in most cases.


1 point by bogomipz 5895 days ago | link

And a third alternative is to use dotted pairs for the associations, but my point was that by treating a plain list as alternating keys and values, it plays nice with rest arguments in functions.

Generally, a list may be interpreted in different ways in different situations, and a common complaint about lisp is that you can't tell if a cons cell is supposed to be the starting point of a tree, an assoc list, a sequence, or something else. I think the way to tackle this in Arc should be to make better use of annotations.

A rest argument will always be a plain list without a tag. That's the reason for the suggested interpretation of kvp!b.

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1 point by nlavine 5894 days ago | link

Why are we assuming that keyword arguments must be passed as flat lists of keywords and values?

  (bar 1 2 ('foo 3) ('baz 4))
I agree the flat way is cleaner, but this is certainly a possibility too.

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1 point by cooldude127 5895 days ago | link

well, you could always just use pairs to turn the interleaved list into an alist.

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1 point by bogomipz 5895 days ago | link

Yes, with the overhead of the operation plus a let form.

My suggestion only really applies if pg decides against adding keyword arguments to Arc.

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2 points by cchooper 5895 days ago | link

Exactly. It's basically a roundabout way of adding keywords into the language. A better idea would be to just add them, and then list-functional notation could be used for something more generally useful.

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