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Date: Fri, 15 May 2009 15:49:45 +0200
From: Florian Hars <hars@bik-gmbh.de>
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To: Joel Christner <joel.christner@gmail.com>
Cc: caml-list@yquem.inria.fr
Subject: Re: [Caml-list] Newbie list question
References: <9da743ed0905131024u53a207f0s9e963be782f3f2c6@mail.gmail.com>
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X-Spam: no; 0.00; hars:01 hars:01 bik-gmbh:01 foo:01 val:01 elt:01 vars:01 foo:01 baz:01 baz:01 val:01 vars:01 abstr:01 elt:01 recursive:01 

Joel Christner schrieb:
> What I'm wanting to do is create a ref list that contains a series of
> strings

Judging from your code, you really do not want to do this (I just sped up
a program of mine by at least two orders of magnitude fixing an error like
that). What you probably want to do is

module S = Set.Make(String);;

let s = ref S.empty;;

let add_variable_ref s v = 
  s := S.add v !s;;

add_variable_ref s "foo";;
add_variable_ref s "bar";;
S.elements !s;;

Even better if you can structure your code to get rid of the ref:

# let add_variable s v = S.add v s;;
val add_variable : S.t -> S.elt -> S.t = <fun>
# let vars = List.fold_left add_variable S.empty ["Foo"; "Bar"; "Baz"; "Foo"; "Qux"; "Baz"];;
val vars : S.t = <abstr>
# S.elements vars;;
- : S.elt list = ["Bar"; "Baz"; "Foo"; "Qux"]

Of course, this works as well, but uses more stack space as right folds are
not tail recursive:

# let vars' = List.fold_right S.add ["Foo"; "Bar"; "Baz"; "Foo"; "Qux"; "Baz"] S.empty;;
val vars' : S.t = <abstr>
# S.elements vars';;
- : S.elt list = ["Bar"; "Baz"; "Foo"; "Qux"]

-- Florian.