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Date: -- (:)
From: Remi VANICAT <vanicat@l...>
Subject: Re: [Caml-list] Newbie question concerning type definitions
"Thomas Link" <t.link.tmp200101@gmx.net> writes:

> Hello, 
> 
> I have hesitated to send this question to this mailing list as I 
> suspect it to be rather stupid. What am I trying to do? I would like to 
> implement a simple stack based language in OCaml in order to get a 
> feeling for OCaml and also to test some ideas. Well, I didn't get far 
> as I wasn't even able to define the basic data structures. I guess this 
> is plain wrong:
> 
> type returnState = Succeeded | Failed | Error of int
> and proc = (stack -> dictionary -> returnState) 
> and procs = proc list 
> and element = 
> 	Int of int 
>   | String of string
>   | Float of float
>   | Word of proc 
> and stack = element Stack.t 
> and dictionary = (string, procs) Hashtbl.t;; 
> 
> When compiling this, the compiler tells me that proc's definition is 
> cyclic. How can I circumvent this in OCaml? 

this is a FAQ (is this FAQ in the FAQ ?)
There is two possible answer :
First add the -rectype option to the compiler to allow such recursive
type, 

Secondly, put the proc type into a constructor :

type returnState = Succeeded | Failed | Error of int
and proc = Proc of (stack -> dictionary -> returnState) 
and procs = proc list 
and element = 
	Int of int 
  | String of string
  | Float of float
  | Word of proc 
and stack = element Stack.t 
and dictionary = (string, procs) Hashtbl.t;; 

-- 
Rémi Vanicat
vanicat@labri.u-bordeaux.fr
http://dept-info.labri.u-bordeaux.fr/~vanicat
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