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3 points by binx 4211 days ago | link | parent

2. Take this function as an example:

(fn (x y) (g x y (fn (x) (h x))))

When inlined with x=1 and y=2, it should be rewritten as:

(g 1 2 (fn (x) (h x))), not

(g 1 2 (fn (x) (h 1)))

Because the second x is not free in the function body.



2 points by almkglor 4211 days ago | link

I see. This is actually handled implicitly in the compiler's AST structure: during the conversion from the list form to the AST form, each local variable is given a unique ID:

  (fn (x y) (g x y (fn (x) (h x))))
  =>
  (fn (x@1 y@2) (g x@1 y@2 (fn (x@3) (h x@3))))
  ; approximation of the AST structure, the AST
  ; is really a table of properties
So mindless replacement of the inlined version will simply replace x@1, not x@3.

  (g 1 2 (fn (x@3) (h x@3)))

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1 point by almkglor 4210 days ago | link

Hmm. Turns out this is a real issue, but for a different reason: since local variables are given unique ID's, we should actually replace local variable ID's for subfunctions when a function is inlined several times:

  (set glob
    (fn (x@1 y@2)
      (g x@1 y@2 (fn (x@3) (h x@3))))
  (glob 1 2)
  (glob 3 4)
  =>
  (set glob
    (fn (x@1 y@2)
      (g x@1 y@2 (fn (x@3) (h x@3))))
  (g 1 2
    (fn (x@4) (h x@4)))
  (g 3 4
    (fn (x@5) (h x@5)))

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