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[Caml-list] mystified by typing of optional arguments
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Date: -- (:)
From: Ville-Pertti Keinonen <will@e...>
Subject: Re: [Caml-list] mystified by typing of optional arguments
> The following example mystifies me
>
> let f ?opt x =
>   match opt with
>   | None -> x
>   | Some dx -> x + dx
>
> let g x = x + 1
>
>
> let h1 = function
>   | 0 -> [g]
>   | _ -> [f; g]
>
>
> let h2 = function
>   | _ -> [f; g]
>
>
> h1 is typable but not h2.
> Why is that ?

The type of the list is inferred from the first element of the first 
instance.

Similarly:

let x = [ g; f ] (* works *)

let x = [ f; g ] (* doesn't work *)

let x = [ (f : int -> int); g ] (* works *)

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