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Type a is not compatible with type 'a #7103

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vicuna opened this Issue Dec 20, 2015 · 3 comments

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vicuna commented Dec 20, 2015

Original bug ID: 7103
Reporter: @hhugo
Assigned to: @garrigue
Status: closed (set by @xavierleroy on 2017-02-16T14:18:06Z)
Resolution: fixed
Priority: normal
Severity: minor
Version: 4.02.3
Fixed in version: 4.03.0+dev / +beta1
Category: typing
Monitored by: @hhugo @gasche

Bug description

the following type error

"Type a is not compatible with type 'a"

should contain the constraint on 'a.

"Type a is not compatible with type 'a = < .. >"
"Type a is not compatible with type 'a = [> `b]"

and eventually not talk about 'a is it's not needed.

Steps to reproduce

OCaml version 4.02.3

type 'a t
type a

let f : < .. > t -> unit = fun _ -> ();;

val f : < .. > t -> unit =

let g : [< `b] t -> unit = fun _ -> ();;

val g : [< `b ] t -> unit =

let h : [> `b] t -> unit = fun _ -> ();;

val h : [> `b ] t -> unit =

let _ = fun (x : a t) -> f x;;

Characters 27-28:
let _ = fun (x : a t) -> f x;;
^
Error: This expression has type a t but an expression was expected of type
(< .. > as 'a) t
Type a is not compatible with type 'a

let _ = fun (x : a t) -> g x;;

Characters 27-28:
let _ = fun (x : a t) -> g x;;
^
Error: This expression has type a t but an expression was expected of type
([< `b ] as 'a) t
Type a is not compatible with type 'a

let _ = fun (x : a t) -> h x;;

Characters 27-28:
let _ = fun (x : a t) -> h x;;
^
Error: This expression has type a t but an expression was expected of type
([> `b ] as 'a) t
Type a is not compatible with type 'a

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vicuna commented Dec 21, 2015

Comment author: @hhugo

see #365

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vicuna commented Dec 21, 2015

Comment author: @garrigue

I'm not sure I understand the problem here.
'a is to be understood in the context of the type printed above, which indicates explicitly what 'a refers to.
It could be possible to print the type once more, but this can be heavy.

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vicuna commented Dec 22, 2015

Comment author: @garrigue

Merged GPR 365.

@vicuna vicuna closed this Feb 16, 2017

@vicuna vicuna added the typing label Mar 14, 2019

@vicuna vicuna added the bug label Mar 20, 2019

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