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2 points by Adlai 5619 days ago | link | parent

I think two is better, because it a) clearly distinguishes it as indentation (rather than just an accidental #\space), and b) it's consistent with the indentation of macros & co.


1 point by shader 5617 days ago | link

Two spaces it is.

Another question:

How do people indent do, and, or, etc.:

a)

  (do abc
      bcd
      cde)
or b)

  (do
    abc
    bcd
    cde)
Choice a is more like a function call, b is more like a macro. Should it be a community standard, or on a user by user basis?

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1 point by CatDancer 5617 days ago | link

I use A, for me the space taken up by the extra indentation is less than the extra line taken up for B.

I don't use indentation as a way to indicate whether I'm calling a function or using a macro.

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1 point by shader 5617 days ago | link

Next question:

Should case be indented like 'if:

  (case
    a
      (b     )
    c
      (d     )
    (e      ))
or in pairs like with:

  (case
     a (b    )
     c (d    )
     (e     ))
?

Should it depend on whether they fit on one line or not? If they don't fit, should it still be like b., just with the second part spilling onto the next line?

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1 point by CatDancer 5617 days ago | link

I use the second if it fits OK, or the first if they don't fit.

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1 point by absz 5616 days ago | link

Ditto, except I write

  (case
    a-short     (b ...)
    c-very-long (d ...)
                (e ...))
when everything is on one line, and

  (case
    a-short
      (b ...)
    c-very-long
      (d ...)
    ; else
      (e ...))
when it doesn't (though I go back and forth about the ; else).

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1 point by shader 5616 days ago | link

Your first version is the one currently implemented by ppr.arc. If you would like, you can write the indentation function for your second version (it can even include the "; else")

Otherwise I think that the first version is generally clearer, and the second is rarely needed, as the value of the case statement can't usually be very long. Could you give me an example where you use your second version?

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1 point by absz 5615 days ago | link

Sure; here's something from my tagged-unions.arc on Anarki (Arc 2). It's responsible for parsing the types specified for slots in the tagged union:

  (each type-frag types
    ; Assemble the ('type name) pairs into two lists, so that we can iterate
    ; through them.
    (case (type type-frag)
      ; If it's a symbol, then we're defining a new name; add a new set of
      ; values, and go.
      sym
        (do
          (zap [cons type-frag _] names)
          (zap [cons nil       _] values))
      ; Otherwise, we're adding a value to an existing variant.
      cons
        ; I changed my mind about the order (now it's (name pred?) instead of
        ; (pred? name)), so I'm reversing it here.
        (zap [cons (rev type-frag) _] (car values))
      ; else
        (err "Invalid member of tagged union declaration.")))
I should also add (just as another data point) that my multi-condition ifs look like that too, and single-condition ifs look like the following:

  (def macexn (n expr)
    " Macroexpand `expr' `n' times.  NB: `expr' *is* evaluated!
      See also [[macex1]] [[macex]] "
    (if (and (number n) (> n 0))
      (macexn (- n 1) (macex1 expr))
      expr))
I'm not hugely wedded to any of my conventions, though, and I haven't coded in Arc for quite a while anyway; this isn't intended to get you to change anything or convert people to my style. As I said, it's just another data point.

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