0003601: "type ... and ..." is not commutative

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0003601

OCaml

OCaml general

public

2005-04-19 15:50

2010-04-30 08:28

Reporter

administrator

Assigned To

garrigue

Priority

normal

Severity

feature

Reproducibility

always

Status

closed

Resolution

fixed

Platform

OS Version

Product Version

Target Version

Fixed in Version

3.12.0+dev

Summary

0003601: "type ... and ..." is not commutative

Description

Full_Name: Francois Pottier
Version: 3.08+alpha1 (2004-07-03)
OS: RedHat Linux 8
Submission from: madiran.inria.fr (128.93.8.77)

Mutually recursive data type definitions, written using "type ... and ...",
are not commutative, even though one might expect them to be. This is
illustrated by the following two code snippets.

Snippet 1:

  # type t = { foo: t} and u = { foo: u };;
  type t = { foo : t; }
  and u = { foo : u; }
  # fun x -> x.foo;;
  - : t -> t = <fun>

Snippet 2:

  # type u = { foo: u } and t = { foo: t };;
  type u = { foo : u; }
  and t = { foo : t; }
  # fun x -> x.foo;;
  - : u -> u = <fun>

Suggested solution: detect that a record label is being defined twice
in this mutually recursive definition and reject the program. Do the
same for data constructors.

Note: this is not a theoretical example! I have actually written code
like this and got a type error much later in the program.

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Notes
(0000256) administrator (administrator) 2005-04-27 14:39	The documentation doesn't say it's supposed to be commutative...

(0005426) garrigue (manager) 2010-04-30 08:02	Added a check for duplicates in revision 10331. This is a hard error. One might prefer a warning, but currently there is no way to use such duplicates.

(0005428) garrigue (manager) 2010-04-30 08:28	After some hesitation, I downgraded it to a warning, as programming style may change in the future. (revision 10332)

Issue History
Date Modified	Username	Field	Change
2005-11-18 10:13	administrator	New Issue
2010-04-30 08:00	garrigue	Status	acknowledged => assigned
2010-04-30 08:00	garrigue	Assigned To	=> garrigue
2010-04-30 08:02	garrigue	Note Added: 0005426
2010-04-30 08:02	garrigue	Status	assigned => resolved
2010-04-30 08:02	garrigue	Fixed in Version	=> 3.12.0+dev
2010-04-30 08:02	garrigue	Resolution	open => fixed
2010-04-30 08:28	garrigue	Note Added: 0005428
2010-04-30 08:28	garrigue	Status	resolved => closed