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From: "Hezekiah M. Carty" <hcarty@atmos.umd.edu>
Date: Sat, 2 Oct 2010 12:09:17 -0400
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Subject: Re: [Caml-list] from if...else to pattern matching
To: ben kuin <benkuin@gmail.com>
Cc: Philip <feucht@uni-koblenz.de>, caml-list@inria.fr
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X-Spam: no; 0.00; val:01 bool:01 beginner's:01 wrote:01 matched:01 caml-list:01 int:01 defined:02 match:02 seems:03 let:03 let:03 pattern:04 anyway:05 matching:05 

On Sat, Oct 2, 2010 at 10:47 AM, ben kuin <benkuin@gmail.com> wrote:
>>
>> # let t x =3D match x with
>> =C2=A0a when x<=3D4 -> true
>> =C2=A0| _ -> false;;
>>
>
> ok, I had a similar attempt with
>
> =C2=A0 =C2=A0let tt x =3D function
> =C2=A0 =C2=A0a when x<=3D4 -> true
> =C2=A0 =C2=A0| _ -> false;;
>
> but that gave me the following (scary =C2=A0-> 'a -> ) signature
>
> =C2=A0 =C2=A0 val tt : int -> 'a -> bool =3D <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 <=3D 4).  The pattern-matched value is never used,
therefore it can be any type.

Hope this helps,

Hez