The option -rectypes

From: Gerd Stolpmann (
Date: Wed Nov 24 1999 - 01:59:36 MET

From: Gerd Stolpmann <>
Subject: The option -rectypes
Date: Wed, 24 Nov 1999 01:59:36 +0100
Message-Id: <99112402223302.32002@ice>

I have some code that compiled in 2.02, but in 2.03 I need the new option
-rectypes of the compilers.

My class definitions look like (the signatures)

class type [ 'node ] extension =
  object ('self)
    method clone : 'self
    method node : 'node
    method set_node : 'node -> unit

class type [ 'ext ] node =
  object ('self)
    constraint 'ext = 'ext node #extension
    method extension : 'ext
    (* ... more methods ... *)

This works in both versions out of the box. If I add

val f : 'a node extension as 'a

the 2.03 compiler only accepts the type if I add -rectypes. I have several

- What is the effect of -rectypes? (I did not find a good explanation in the
- What is the background of this change?
- I have thought about the type 'a node extension as 'a. If I apply the
  constraint of "node", the condition must hold that
      ('a node extension as 'a) node extension
  unifies with
      ('a node extension as 'a) node #extension
  Normally, a closed class type does not unify with an open class type,
  and I wonder why this is accepted at all.

  Without -rectypes, the 2.03 compiler only accepts
      val f : 'a node #extension as 'a
  but this is a much more difficult type.


Gerd Stolpmann      Telefon: +49 6151 997705 (privat)
Viktoriastr. 100             
64293 Darmstadt     EMail: (privat)

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