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|
(* TEST
expect;
*)
type 'a ty =
| Int : int ty
| Bool : bool ty
let fbool (type t) (x : t) (tag : t ty) =
match tag with
| Bool -> x
;;
[%%expect{|
type 'a ty = Int : int ty | Bool : bool ty
Lines 6-7, characters 2-13:
6 | ..match tag with
7 | | Bool -> x
Warning 8 [partial-match]: this pattern-matching is not exhaustive.
Here is an example of a case that is not matched:
Int
val fbool : 't -> 't ty -> 't = <fun>
|}];;
(* val fbool : 'a -> 'a ty -> 'a = <fun> *)
(** OK: the return value is x of type t **)
let fint (type t) (x : t) (tag : t ty) =
match tag with
| Int -> x > 0
;;
[%%expect{|
Lines 2-3, characters 2-16:
2 | ..match tag with
3 | | Int -> x > 0
Warning 8 [partial-match]: this pattern-matching is not exhaustive.
Here is an example of a case that is not matched:
Bool
val fint : 't -> 't ty -> bool = <fun>
|}];;
(* val fint : 'a -> 'a ty -> bool = <fun> *)
(** OK: the return value is x > 0 of type bool;
This has used the equation t = bool, not visible in the return type **)
(* not principal *)
let f (type t) (x : t) (tag : t ty) =
match tag with
| Int -> x > 0
| Bool -> x
;;
[%%expect{|
val f : 't -> 't ty -> bool = <fun>
|}, Principal{|
Line 4, characters 12-13:
4 | | Bool -> x
^
Error: This expression has type t = bool
but an expression was expected of type bool
This instance of bool is ambiguous:
it would escape the scope of its equation
|}];;
(* val f : 'a -> 'a ty -> bool = <fun> *)
(* fail for both *)
let g (type t) (x : t) (tag : t ty) =
match tag with
| Bool -> x
| Int -> x > 0
;;
[%%expect{|
Line 4, characters 11-16:
4 | | Int -> x > 0
^^^^^
Error: This expression has type bool but an expression was expected of type
t = int
|}, Principal{|
Line 4, characters 11-16:
4 | | Int -> x > 0
^^^^^
Error: This expression has type bool but an expression was expected of type
t = int
This instance of int is ambiguous:
it would escape the scope of its equation
|}];;
(* Error: This expression has type bool but an expression was expected of type
t = int *)
(* OK *)
let g (type t) (x : t) (tag : t ty) : bool =
match tag with
| Bool -> x
| Int -> x > 0
;;
[%%expect{|
val g : 't -> 't ty -> bool = <fun>
|}];;
let id x = x;;
let idb1 = (fun id -> let _ = id true in id) id;;
let idb2 : bool -> bool = id;;
let idb3 ( _ : bool ) = false;;
let g (type t) (x : t) (tag : t ty) =
match tag with
| Bool -> idb3 x
| Int -> x > 0
;;
[%%expect{|
val id : 'a -> 'a = <fun>
val idb1 : bool -> bool = <fun>
val idb2 : bool -> bool = <fun>
val idb3 : bool -> bool = <fun>
val g : 't -> 't ty -> bool = <fun>
|}];;
let g (type t) (x : t) (tag : t ty) =
match tag with
| Bool -> idb2 x
| Int -> x > 0
;;
[%%expect{|
val g : 't -> 't ty -> bool = <fun>
|}];;
|
