0005224: Confusing error message at object type definition - MantisBT

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ID

Project

Category

View Status

Date Submitted

Last Update

0005224

OCaml

OCaml general

public

2011-02-14 10:06

2012-06-01 07:13

Reporter

furuse

Assigned To

garrigue

Priority

normal

Severity

minor

Reproducibility

always

Status

closed

Resolution

fixed

Platform

OS

OS Version

Product Version

3.11.2

Target Version

Fixed in Version

4.00.0+dev

Summary

0005224: Confusing error message at object type definition

Description

type 'x t = < f : 'y. 'y t >

gives me an error. I do not understand why this is rejected, but the reason is not the issue. The problem is the error message:

Error: In the definition of t, type 'a t should be 'b t

This should be printed as type 'y t should be 'x t .

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Relationships

Notes
(0007481) protz (manager) 2012-05-31 13:57	This is rejected because this type is non-regular, i.e. it is a parameterized structural type where which is instanciated with a different type parameter. This is also the reason why the code snippet below is rejected: # type 'a foo = [`A \| `B of ('a foo) foo];; Error: In the definition of foo, type 'a foo foo should be 'a foo The solution is to define an intermediary nominal type: type 'a tmp = T of 'a t Then: type 'x t = < f : 'y. 'y tmp > Of course you need these two types to be mutually recursive. # type 'a tmp = Tmp of 'a t and 'a t = < f: 'y. 'y tmp >;; type 'a tmp = Tmp of 'a t and 'a t = < f : 'y. 'y tmp >

(0007492) garrigue (manager) 2012-06-01 07:13	Fixed in trunk and 4.00, revisions 12533 and 12534.

Issue History
Date Modified	Username	Field	Change
2011-02-14 10:06	furuse	New Issue
2011-05-17 16:16	doligez	Status	new => acknowledged
2012-05-31 11:21	frisch	Severity	major => minor
2012-05-31 13:57	protz	Note Added: 0007481
2012-06-01 07:13	garrigue	Note Added: 0007492
2012-06-01 07:13	garrigue	Status	acknowledged => closed
2012-06-01 07:13	garrigue	Assigned To	=> garrigue
2012-06-01 07:13	garrigue	Resolution	open => fixed
2012-06-01 07:13	garrigue	Fixed in Version	=> 4.00.0+dev

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