Original bug ID: 4745
Reporter: silroquen
Status: closed (set by @garrigue on 2009-03-16T04:25:41Z)
Resolution: fixed
Priority: normal
Severity: minor
Version: 3.11.0
Fixed in version: 3.11.1+dev
Category: ~DO NOT USE (was: OCaml general)
Monitored by: @yakobowski

Bug description

Here is a simple linked list type:

type 'a linked_list = 'a node option
and 'a node = {
value : 'a;
next : 'a linked_list;
}

and three apparently equivalent functions to find the linked list's last node:

let rec find_end_a = function
| None -> None
| Some {next = None} as li -> li
| Some node -> find_end_a node.next

let rec find_end_b = function
| None -> None
| Some {next = None} as li -> li
| Some {next = n} -> find_end_b n

let rec find_end_c = function
| None -> None
| Some {next = None} as li -> li
| Some {next = Some n} -> find_end_c (Some n)

Note that the inferred type for find_end_a and find_end_b is
'_a linked_list -> '_a node option
but, for find_end_c:
'a node option -> 'a node option

It seems like all three functions should have the type of find_end_c.

Additional information

Note that if the linked_list type is eliminated, so instead

type 'a node = {
value : 'a;
next : 'a node option
}

then the functions find_end_* all have type
'a node option -> 'a node option
as expected.