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"Fatal error: types should not include variables" #6158

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vicuna opened this issue Sep 4, 2013 · 1 comment
Closed

"Fatal error: types should not include variables" #6158

vicuna opened this issue Sep 4, 2013 · 1 comment
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@vicuna
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@vicuna vicuna commented Sep 4, 2013

Original bug ID: 6158
Reporter: @yallop
Assigned to: @garrigue
Status: closed (set by @xavierleroy on 2015-12-11T18:24:06Z)
Resolution: fixed
Priority: normal
Severity: minor
Version: 4.01.0+beta/+rc
Fixed in version: 4.01.0+dev
Category: typing

Bug description

The following code should be rejected but triggers an internal error:

$ cat vars.ml
type 'a t = T of 'a
type 'a s = S of 'a

type (_, _) eq = Refl : ('a, 'a) eq

let f : (int s, int t) eq -> unit = function
| Refl -> ()
$ ocamlc vars.ml

Fatal error: types should not include variables
Fatal error: exception Misc.Fatal_error

A similar example with well-typed code gives the same error:

$ cat vars2.ml
type (_, _) eq = Refl : ('a, 'a) eq

module M (S : sig
type 'a t = T of 'a
type 'a s = T of 'a
end) =
struct
let f : ('a S.s, 'a S.t) eq -> unit = function
| Refl -> ()
end
$ ocamlc vars2.ml

Fatal error: types should not include variables
Fatal error: exception Misc.Fatal_error

@vicuna
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@vicuna vicuna commented Sep 5, 2013

Comment author: @garrigue

Fixed in trunk and 4.01, revision 14064.

Indeed, the incompatibility check is more clever than before, but as a result it may be called on type definitions containing variables. No need to fail in that case.

Keep this PR open, as there is a minor side-problem, as the non-principal typechecker may leave reified variables in exported types. They are detected and report when using -principal.
While it would be better to do that without -principal too, this has no impact on soundness.

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