Arc Forumnew | comments | leaders | submitlogin
1 point by cchooper 6152 days ago | link | parent

Doesn't work I'm afraid:

  (= pre 'blub)

  (your-def-with-prefix pre foo (x) (+ 1 x))
  => #<procedure: pre-foo>

  (my-def-with-prefix pre foo (x) (+ 1 x))
  => #<procedure: blub-foo>
Without being able to take the prefix from the value of a variable, the whole macro is pointless.


1 point by eds 6152 days ago | link

Then why don't you just eval prefix?

  `(def ,(read (+ (coerce (eval prefix) 'string) "-" (coerce name 'string))) ,args ,@body)
It's still much less clunky than expanding the whole def under an eval.

-----

1 point by cchooper 6152 days ago | link

Still has a bug:

  (let pre2 'blub (your-def-with-prefix pre2 foo (x) (+ 1 x)))
  => Error: "reference to undefined identifier: _pre2"

-----

2 points by cooldude127 6152 days ago | link

that's because the macro gets expanded (and thus eval is called on pre2) before the let form is evaluated.

-----

1 point by eds 6152 days ago | link

Yeah, I see the problem with that.

cchooper, did you actually ever run your version? I can't make your orginal version work.

  arc> (def-with-prefix pre foo (x) (+ 1 x))
  Error: "reference to undefined identifier: _x"
And looking at the macro expansion, I'm not at all surprised:

  arc> (macex '(def-with-prefix pre foo (x) (+ 1 x)))
  (eval (list (quote def) ; my indentation
              (read (+ (coerce pre (quote string)) "-" (coerce (quote foo) (quote string))))
              (x) (+ 1 x)))
args and body would need to be quoted for this to work properly. And then it admittedly does what it is supposed to, but it becomes even uglier.

  (mac def-with-prefix (prefix name args . body)
    `(eval (list 'def
            (read (+ (coerce ,prefix 'string)
                     "-"
                     (coerce ',name 'string)))
            ',args
            ,@(map [list 'quote _] body))))

-----

1 point by cchooper 6151 days ago | link

Hmmm... it worked last night. I must have made a mistake when I copied it into the comment. Thanks for catching it.

Here's a slightly less clunky version:

  (mac def-with-prefix (prefix name args . body)
    `(eval (join (list 'def 
                  (sym (+ (coerce ,prefix 'string)
                          "-"
                          (coerce ',name 'string)))
                  ',args)
            ',body)))
I also tried doing it with nested quasiquotes but that just looked worse.

-----

1 point by shiro 6152 days ago | link

Ah, I got it.

-----