Arc Forum | Yeah, but env just keeps the variables around, not their values. It's used to d...

Arc Forum

1 point by fallintothis 5435 days ago | link | parent

Yeah, but env just keeps the variables around, not their values. It's used to distinguish between locals and globals when compiling down to lambda.

  > (ac '(fn (x) (+ x 1)) '())
  (lambda (x) (ar-funcall2 _+ x 1))
  > (ac '(+ x 1) '())
  (ar-funcall2 _+ _x 1)
  > (ac '(+ x 1) '(x))
  (ar-funcall2 _+ x 1)

So it's not quite what you'd want. Off the top of my head, you could hack ac.scm to treat

  (fn (x) body)

as something like

  (fn (x) (= (locals* 'x) x) body (wipe (locals* 'x)))

Since Arc does all of its local binding with fn (either directly or by macroexpansion), this would work. ac.scm won't heed Arc-side redefinitions of fn, so I can't think of a convenient vanilla Arc implementation. As for efficiency, thread safety, etc., my idea seems gross.

I know Common Lisp has environments (http://www-prod-gif.supelec.fr/docs/cltl/clm/node102.html), but I don't know how they're usually implemented.

  $ clisp -q
  [1]> (let ((x 10)) (let ((y 20)) (the-environment)))
  #(#(Y 20 #(X 10 NIL))
    NIL
    NIL
    NIL
    ((DECLARATION XLIB::CLX-VALUES VALUES OPTIMIZE DECLARATION)))