Original bug ID: 7068
Reporter: lavi
Status: closed (set by @xavierleroy on 2017-02-16T14:18:22Z)
Resolution: not a bug
Priority: normal
Severity: major
Version: 4.02.3
Target version: 4.03.0+dev / +beta1
Category: ~DO NOT USE (was: OCaml general)
Monitored by: @gasche

Bug description

Manual http://caml.inria.fr/pub/docs/manual-ocaml-4.02/libref/Lazy.html says:

Note: if the program is compiled with the -rectypes option, ill-founded recursive definitions of the form let rec x = lazy x or let rec x = lazy(lazy(...(lazy x))) are accepted by the type-checker and lead, when forced, to ill-formed values that trigger infinite loops in the garbage collector and other parts of the run-time system. Without the -rectypes option, such ill-founded recursive definitions are rejected by the type-checker.

The last sentence is over optimistic:

module rec A : sig
type t = B.t Lazy.t
val x : t
end = struct
type t = B.t Lazy.t
let x = lazy B.x
end and B : sig
type t
val x : t
end = struct
type t = A.t
let x = A.x
end

let y = Lazy.force A.x