Arc Forumnew | comments | leaders | submitlogin
1 point by shader 5674 days ago | link | parent

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?



1 point by CatDancer 5674 days ago | link

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

-----

1 point by absz 5672 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).

-----

1 point by shader 5672 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?

-----

1 point by absz 5672 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.

-----