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2 points by rntz 4323 days ago | link | parent

On the basic datatypes of arc: you cannot remove symbols or lists from arc. Then it would no longer be a lisp. I suppose you could just have strings be symbols or vice-versa, but then you either put overhead on usage of strings for variable lookup or overhead on usage of symbols for string manipulation.


2 points by sacado 4323 days ago | link

Yes, but, for example, association lists could be implemented as hash tables while beeing seen and manipulated as regular lists. That's tricky, but that should be feasible. And Clojure removed cons cells and thus "traditional" lists, but it's still a Lisp...

As for strings and symbols, I don't really know how they are actually implemented, but as far as I know, the idea is that 'foo and 'foo are the same memory location, while "foo" and "foo" are not necessarily the same object(thus allowing string mutation). Or maybe I'm wrong ?

Lua's strings are implemented the same way : "foo" is always the same location as any other "foo" and string manipulation really doesn't seem to be a problem at all...

I really think "foo" could be just an alternate syntax for 'foo (just as |foo| is) so that we still have a Lisp... Add string manipulation facilities to symbols, and you're done. In any case, characters just seem useless...

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3 points by almkglor 4322 days ago | link

> Yes, but, for example, association lists could be implemented as hash tables while beeing seen and manipulated as regular lists.

    (= foo '((key1 . val1) (key2 . val2)))
    (= bar (cons '(key2 . different-val2) foo))
    bar
    => ((key2 . different-val2) (key1 . val1) (key2 . val2))
Hmm.

Probably means we want to have some sort of "source" slot too, so that we can display shadowed values. Hmm. The association sublists e.g. '(key1 . val1) can probably be directly shared, but lists also imply an ordered set, so we need to store that info too. Hmm.

>As for strings and symbols, I don't really know how they are actually implemented, but as far as I know, the idea is that 'foo and 'foo are the same memory location, while "foo" and "foo" are not necessarily the same object(thus allowing string mutation)

This is correct. And when you really look at it, changing strings as if they were arrays of characters is hardly ever done in Arc; usually what's done is we just read them off as an array of characters and build a new string.

> In any case, characters just seem useless...

Another lisplike, Skill, uses 1-char length symbols for characters (i.e. no separate character type). Also, many of its string manip functions also accept symbols (although they still all return strings).

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1 point by sacado 4322 days ago | link

  >  => ((key2 . different-val2) (key1 . val1) (key2 . val2))
When you don't know why your design's wrong, ask almkglor :)

Ok, well it's probably a little trickier than I thought... Maybe a dual implementation, as you suggest, would work then...

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3 points by stefano 4322 days ago | link

Another point to consider is that if your a-list is very small (<= 5 elements) it could be faster than hash tables. The sharing behavior could be achieved with some sort of concatenated hash-tables, a list of tables to consider in turn to find the desired element. This seems very slow though. BTW, removing a-lists would be useless: they're so simple to implement that a lot of developers (me included) would re-invent them to use in their applications.

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1 point by almkglor 4322 days ago | link

LOL

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3 points by gnaritas 4322 days ago | link

My two cents on strings/symbols, there are semantic reasons they should always be separate. It's not about string mutation, ignore the implementation, it isn't relevant.

Two symbols 'foo can always be considered to mean the same thing, two strings "foo" can't, they may be only the same by coincidence. This matters if automated refactoring tools become available because you can safely rename all occurrences of a symbol, the same cannot be said of strings.

Mixing strings and symbols is a bad idea, they are different things and should remain that way.

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1 point by sacado 4322 days ago | link

Well, we could at least have a very lightweight bridge between both worlds, by allowing (and automatically converting) symbols into string where strings are needed and vice versa.

Code crashing because, for instance, you tried to concatenate a string and a symbol is rather annoying, but these bugs keep happening and the developer's intention is rather obvious there.

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4 points by gnaritas 4322 days ago | link

Oh I don't disagree, I'm actually a Smalltalker and I'm accustomed to Symbol being a subclass of String and a String being a list of Characters. I actually have refactoring tools so I just wanted to point out that they are different for more than just implementation reasons and there's a logical reason to have symbols beyond mere optimization.

I just hang out here because I like to see how a new Lisp is born and how you guys think, even though I don't actually use Arc.

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