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2 points by nex3 6119 days ago | link | parent

Agreed. Ruby does it the other way ("abcde"[1..-1] is "bcd"), but that's only because there's no other way to specify "until the end." But that's the default in Arc; the following are equivalent right now:

  (cut "abcde" 1 -1)
  (cut "abcde" 1)


3 points by lsb 6119 days ago | link

Nope, Ruby has -1 at the end:

    $ irb
    >> "abcde"[1..-1]
    => "bcde"
    >>

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4 points by nex3 6119 days ago | link

Oh, right. That's what I meant.

So, to clarify: I think arc should not do it Ruby-style, but rather have

  arc> (cut "abcde" 1 -1)
  "bcd"

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2 points by mec 6119 days ago | link

How would you then decide 0 0?

  arc> (cut "abcde" 0 0)
  "a"
  arc> (cut "abcde" 0 0)
  "abcde"
-1 should deffinitly refer to the last elemental or I don't see a way to get it.

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3 points by nex3 6119 days ago | link

(cut s 0 0) should return the empty string, just like (cut s 1 1) and (cut s 42 42). Which it does in either implementation.

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2 points by vincenz 6119 days ago | link

Then you would need -0 to get the full string. You're not making sense.

How do you propose to get "bcde" from "abcde"?

Either you need -0, or your final 0 is ambiguous.

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3 points by nex3 6119 days ago | link

No you don't - the full string is the default.

  > (cut "abcde" 1)
  "bcde"

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3 points by tokipin 6119 days ago | link

i was thinking that too, but how would you do it dynamically (eg with variables) ?

  (cut "abcde" begin end)
what would i need to put in end to get the full string? nil?

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3 points by sjs 6119 days ago | link

Both nil and (len str) work. I see both sides of the argument as counting from -1 eliminates the 0 corner case.

I like indices that are intuitive with literal numbers. Counting from 0 at one end and from 1 at the other is jarring. When -1 points to the end of string rather than before the last char (cut str 0 (- (len str))) returns the first char instead of the empty string.

With -1 -> before last char:

  (def chop ((o str "abcdef"))
    (pr "Chop how many chars off the end of \"" str "\"? ")
    (= n (coerce (cut (readline) 1) 'int)) ; bug in readline prepends #\newline
    (prn "Chopped: \"" (if (is n 0) str (cut str 0 (- n))) "\"")) ; handle corner case
With -1 -> end of string:

  (def chop ((o str "abcdef"))
    (pr "Chop how many chars off the end of \"" str "\"? ")
    (= n (coerce (cut (readline) 1) 'int)) ; bug in readline prepends #\newline
    (prn "Chopped: \"" (cut str 0 (- -1 n)) "\"")) ; no corner case, but there's this -1 there
I probably made a stronger argument for -1 pointing to the end of string as it leads to shorter code.

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2 points by nex3 6119 days ago | link

If you absolutely need to do that, you can just use (len str).

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3 points by akkartik 6119 days ago | link

Yup. Which is how python does it.

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2 points by jules 6119 days ago | link

    $ irb
    >> "abcde"[1...-1]
    => "bcd"

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