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Re: [Caml-list] getting the type of a polymorphic data ?
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 Date: -- (:) From: Diego Olivier Fernandez Pons Subject: Re: [Caml-list] getting the type of a polymorphic data ?
```    Bonjour,

> # type 'a result = 'a * string;;
> # let new_result (a:'a) description = ((a,description) : 'a result);;
> val new_result : 'a -> string -> 'a result = <fun>
> # let print_int ((a,d): int result) = Printf.printf "%s is %d\n%!" d a;;
> val print_int : int result -> unit = <fun>
> # let print_float = ...
> # let x = new_result 10 "the number of elements in the knapsack";;
> val x : int result = ...
> # print_int x;;
> the number of elements in the knapsack is 10
> - : unit = ()

Here is the problem of this approach

# let complex_computation = fun x y -> x + y
val complex_computation : int -> int -> int = <fun>

let x = simple_computation () and
y = simple_computation ()

let z = complex_computation x y

Now I what to add a comment to x to print intermediate results and
check the first computation is correct. In your approach, this lifts x
: int on x : int result. But what will then be the type of
complex_computation ?

int result -> int -> int ?
int -> int result -> int ?
int result -> int result -> int ?
int result -> int result -> int result ?

Diego Olivier

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```