Original bug ID: 1137
Reporter: administrator
Status: closed
Resolution: fixed
Priority: normal
Severity: minor
Category: ~DO NOT USE (was: OCaml general)

Bug description

Hi,
I'm not sure if anyone caught this from the mailing list, but in case
no one did, here is the original mail
http://caml.inria.fr/archives/200204/msg00363.html
from Nadji Gauthier.

 The reason I think it is a bug is that the type error only shows up

when the marked Printf line is uncommented from pvmain.ml, but it compiles
fine when the Printf isn't there. The error report is

File "pvmain.ml", line 4, characters 11-22:
The type of this expression, [ D2 of [ D3 of [ `U]]] Pvdim.dec,
contains type variables that cannot be generalized

(* pvmain.ml *)

open Pvdim

let x120 = (d0 (d2 (d1 dec)))
let x32 = (d2 (d3 dec)) (* <--- Bug shows up here! *)
let f_nz (x:[< 'a digit ] dec) = to_int x
let x0 = dec and x1 = (d1 dec)
type 'a atleast5 =
[ D5 of 'a | D6 of 'a | D7 of 'a | D8 of 'a | D9 of 'a ] and 'a atmost4 = [D0 of 'a | D1 of 'a | D2 of 'a | D3 of 'a | D4 of 'a ]
let f_atleast5 (x:[<
| [< 'a digit ] atmost4
| [< `U | 'a digit ] atleast5] dec) = to_int x

let _ =
Printf.printf "Result should be 32, is %d\n" (Pvdim.to_int x32);
(* ^^^ Uncomment this Printf to reveal bug ^^^
Printf.printf "Result should be 32, is %d\n" (f_atleast5 x32);
*)
()

(* pvdim.mli *)
type 'a dec

val dec : [`U] dec
val to_int : 'a dec -> int

type 'a digit =
[D0 of 'a | D1 of 'a | D2 of 'a | D3 of 'a | D4 of 'a | D5 of 'a | D6 of 'a | D7 of 'a | D8 of 'a | D9 of 'a ]

val d0 : ([< 'a digit ] as 'd) dec -> [D0 of 'd] dec val d1 : 'a dec -> [D1 of 'a] dec
val d2 : 'a dec -> [D2 of 'a] dec val d3 : 'a dec -> [D3 of 'a] dec
val d4 : 'a dec -> [D4 of 'a] dec val d5 : 'a dec -> [D5 of 'a] dec
val d6 : 'a dec -> [D6 of 'a] dec val d7 : 'a dec -> [D7 of 'a] dec
val d8 : 'a dec -> [D8 of 'a] dec val d9 : 'a dec -> [D9 of 'a] dec

(* pvdim.ml *)
type 'a digit =
[ D0 of 'a | D1 of 'a | D2 of 'a | D3 of 'a | D4 of 'a | D5 of 'a | D6 of 'a | D7 of 'a | D8 of 'a | D9 of
'a ]
type 'a dec = int

let dec = 0
let to_int x = x

let mkd n = fun d -> d * 10 + n
let d0, d1, d2, d3, d4, d5, d6, d7, d8, d9 =
mkd 0, mkd 1, mkd 2, mkd 3, mkd 4, mkd 5, mkd 6, mkd 7, mkd 8, mkd 9

-- Brian