0004907: Type manifests do not support type variable substitutions

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Date Submitted

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0004907

OCaml

OCaml general

public

2009-11-02 16:24

2012-06-01 09:32

Reporter

mottl

Assigned To

garrigue

Priority

normal

Severity

feature

Reproducibility

always

Status

assigned

Resolution

open

Platform

OS Version

Product Version

3.11.1

Target Version

Fixed in Version

Summary

0004907: Type manifests do not support type variable substitutions

Description

The following would seem like a perfectly legitimate thing to do:

  type ('a, 'b) t = { a : 'a; b : 'b }
  type ('a, 'b) u = ('a, 'b option) t = { a : 'a; b : 'b option }

Unfortunately, the compiler fails with:

  File "foo.ml", line 3, characters 5-63:
  Error: The variant or record definition does not match that of type
  ('a, 'b option) t

This does not quite seem correct.

This restriction makes it impossible to e.g. repeat a type definition in a more specialized way such that the preprocessor can exploit the extra syntactic representation to generate code more flexibly from the type definition.

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Notes
(0005191) doligez (manager) 2009-12-09 17:35	The problem is that a record type declaration is generative, so your second record type is not an instance of the first. Can this be changed without major changes to the typechecker? I don't know.

Issue History
Date Modified	Username	Field	Change
2009-11-02 16:24	mottl	New Issue
2009-12-09 17:35	doligez	Note Added: 0005191
2009-12-09 17:35	doligez	Severity	minor => feature
2009-12-09 17:35	doligez	Status	new => acknowledged
2012-06-01 09:32	garrigue	Assigned To	=> garrigue
2012-06-01 09:32	garrigue	Status	acknowledged => assigned