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Toplevel doesn't accept the type info it writes itself. #5155

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vicuna opened this issue Sep 26, 2010 · 3 comments
Closed

Toplevel doesn't accept the type info it writes itself. #5155

vicuna opened this issue Sep 26, 2010 · 3 comments
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@garrigue
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bug suspended
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4.01.0

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@vicuna
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vicuna commented Sep 26, 2010

Original bug ID: 5155
Reporter: yziquel
Assigned to: @garrigue
Status: resolved (set by @damiendoligez on 2012-09-19T12:13:05Z)
Resolution: suspended
Priority: normal
Severity: minor
Version: 3.12.0
Target version: 4.01.0+dev
Category: ~DO NOT USE (was: OCaml general)

Bug description

Here's a type declaration that is accepted. However the type information that is returned isn't accepted by the toplevel.

yziquel@seldon:~$ ocaml
Objective Caml version 3.12.0

type 'a t = private ( < .. > as 'a);;

type 'a t = private < .. > constraint 'a = 'a t

type 'a t = private < .. > constraint 'a = 'a t;;

Error: The type constraints are not consistent.
Type 'a is not compatible with type 'a t
@vicuna
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vicuna commented Oct 2, 2010

Comment author: @garrigue

I admit the situation is confusing.
However, I have no easy fix at this point.
Parsing of type expressions is so complicated that fixing this is bound to break something else...

Two remarks:

  1. I'm afraid this definition is not what you intended. It defines a private row type, whose parameter is constrained to be itself. This is not a private abbreviation, and actually this type ends up not being usable.
  2. If you want a private abbreviation, the declaration should be
    type 'a t = 'a constraint 'a = < .. >
    This version gets printed correctly.

@vicuna
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vicuna commented Oct 3, 2010

Comment author: yziquel

Thanks. I believe that

type 'a t = 'a constraint 'a = < .. >

is indeed what I want. Couldn't it be possible to make the toplevel print this type declaration instead of the following?

type 'a t = < .. > constraint 'a t = 'a

It seems to me that the main issue is the fact that 'a is implicit in < .. >. Wouldn't it be better to have a way to make it explicit? Like < .. as 'a >?

@vicuna
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vicuna commented Sep 19, 2012

Comment author: @damiendoligez

This type definition is not accepted anymore in 4.00.0, so the problem disappeared.

@vicuna vicuna closed this as completed Sep 19, 2012
@vicuna vicuna added this to the 4.01.0 milestone Mar 14, 2019
@vicuna vicuna added the bug label Mar 20, 2019
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