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2 points by tokipin 6153 days ago | link | parent

my guess is it avoids it because it's ugly. i may be in the minority for thinking that's a good reason


5 points by byronsalty 6153 days ago | link

Well I don't think it's ugly, but ugliness aside it's very descriptive in one char. I'd personally like to see this convention carried over. Ruby uses the same convention so it's not just Scheme.

If this was intentionally left out my guess would be that PG was trying to save those chars for something meaningful to the compiler (syntax) not for aesthetics.

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1 point by are 6152 days ago | link

It should be possible to detect, at define-time, whether a function/macro has side-effects (see the ideas for a conservative purity analyzer in http://arclanguage.org/item?id=558).

So if the function/macro has side-effects, def/mac could e.g. also assign it to a second symbol with "!" appended.

'?' could also be done similarly, but would be more difficult. Here is a start:

def/mac should also assign its function/macro to a second symbol with "?" appended if:

1) The function/macro has no side-effects (no "!")

2) The function/macro has a least one argument

3) The function/macro could return the empty list

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1 point by Jekyll 6149 days ago | link

join? ?

list? ?

sort? ?

first? ?

It's not doing it for me.

Leaving aside the issues of detecting a query, I think it's a really bad idea to have the compiler force (badly guessed) semantic knowledge on me.

It's my code, I wrote it, and I don't want any compiler telling me that a query that caches previous results must be imperative! and not end in a ? .

I also thing needlessly polluting a namespace with addition symbols is a bad idea. You only get one namespace in arc, try to preserve it for the future.

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1 point by tokipin 6153 days ago | link

that makes sense. '!' is already being used (though the convention doesn't interfere with the syntax at the moment)

bear with me here, but '!' means the function isn't pure, right? if so, who cares? it seems like an ivory tower thing. ? is fine, though maybe prefix notation can be considered

  isPair
  isNumber
  dangerSet
  dangerSet-car

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5 points by absz 6153 days ago | link

Just because something is academic doesn't mean it's not worthwhile. For instance, map, keep, reduce, etc. are different if passed a function with side-effects. What happens if you give them a function which modifies the list as it's being traversed? A pathological example:

  arc> (= x (range 1 5))
  (1 2 3 4 5)
  arc> (map [do (= (cdr x) (cddr x)) _] x)
  (1 3 4 5)
  arc> x
  (1)
However, if map is passed a pure function, you can e.g. run one copy of the function on each core and run it in parallel.

And "dangerSet" is both non-Lispy and non-Arcy. It's non-Arcy because it's long. And it's non-Lispy because of that capital letter: danger-set would be marginally better. But nevertheless, pair? is shorter than is-pair, and (in my opinion) reads much more nicely.

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9 points by im 6153 days ago | link

You may be in the minority for thinking it's ugly.

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