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[Caml-list] C style for loop
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Date: -- (:)
From: Jeff Henrikson <jehenrik@y...>
Subject: [Caml-list] C style for loop
Okay, so maybe I should be more specific about what I want in a "C-style for loop."  Its readablity merits are hopefully self
evident.  Well, unless you're a compulsive CPS addict who wishes even his grocery list could be written to tail recurse. . .

Suppose

(*  loop var | init val | while | expr for next val *)
for     c         0      (c<10)        (c+1)         do
  (* bla *)
done;

desugars into:

let rec iter_gensymXXX c =
  (* bla *)
  let c = (c+1) in
    if (c<10) then iter_gensymXXX c else ()
  in
iter_gensymXXX 0


Then we could write nice readable nested loops for square arrays, etc.  And then there's the canonical loop form which enters in a
place different from the exit test.  For that, C style "break" is a readable idiom:


for c 0 true c do
  (* bla1 *)
  let c = c+1 in
    if !(c<10) then break;
  (* bla2 *)
end;

could desugar into:

let rec iter_gensymXXX c =
  (* bla1 *)
  let c = c+1 in
    if !(c<10) then
	()
    else begin
      (* bla2 *)
	let c = c in
	  if true then iter_gensymXXX c else ()
    end
 in
 iter_gensymXXX 0


The transformation for "continue" is similar.

Pardon my laziness, camlp4 looks really cool, but I haven't taken the time to learn it.  For the time being, if somebody has
already written a macro kind of like this, I'll take it.  IMHO it would be a boon to the caml community to have a standard form for
this.  Even if it were only a "style guide" addition or what have you.


Jeff Henrikson


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