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From: "Hezekiah M. Carty" <hcarty@atmos.umd.edu>
To: ben kuin <benkuin@gmail.com>
Cc: Philip <feucht@uni-koblenz.de>, caml-list@inria.fr
Subject: Re: [Caml-list] from if...else to pattern matching
Date: Sat, 2 Oct 2010 12:09:17 -0400	[thread overview]
Message-ID: <AANLkTimp6OxMnYKrjon1=EnaS4OpCf9sHvQVVyo6D9e=@mail.gmail.com> (raw)
In-Reply-To: <AANLkTikkFytjyRzE=_NJUq2g6KV6wAR8v7QOwyshHUnj@mail.gmail.com>

On Sat, Oct 2, 2010 at 10:47 AM, ben kuin <benkuin@gmail.com> wrote:
>>
>> # let t x = match x with
>>  a when x<=4 -> true
>>  | _ -> false;;
>>
>
> ok, I had a similar attempt with
>
>    let tt x = function
>    a when x<=4 -> true
>    | _ -> false;;
>
> but that gave me the following (scary  -> 'a -> ) signature
>
>     val tt : int -> 'a -> bool = <fun>
>
> so I stopped
>
> thanks anyway
>

This seems to be a common beginner mistake (hence the reference to the
beginner's list).  You defined tt as a function which takes two
arguments, x and another matched by "function" - which tt ignores the
value of (a when x <= 4).  The pattern-matched value is never used,
therefore it can be any type.

Hope this helps,

Hez


  reply	other threads:[~2010-10-02 16:09 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-10-02 14:04 ben kuin
2010-10-02 14:22 ` [Caml-list] " Philip
2010-10-02 14:47   ` ben kuin
2010-10-02 16:09     ` Hezekiah M. Carty [this message]
2010-10-02 17:54 ` Jon Harrop

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