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Date: Fri, 19 Sep 2003 11:22:52 -0400
To: Richard Jones <rich@annexia.org>
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] Subclasses and pattern matching
Message-ID: <20030919152252.GA30989@henchmonkey.org>
References: <20030919142156.GA30187@henchmonkey.org> <20030919145220.GD4205@redhat.com>
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From: katre <katre@henchmonkey.org>
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Richard Jones wrote:
> 
> Possibly I'm being dumb here, but wouldn't it be better to use
> a union type, eg:
> 
> type num = Int of int | Float of float
> 

Yes, except for two facts:

a) Each different type has different data available (some are ints, some
strings, some more complex)
b) Each different type has a lot of data.  I don't really want to
specify a 10-member tuple for each constructor :)
c) Where the data is used, I want to match two or three different types,
and then call a default method with anything left over.  With a union, I
have to deal with every possible type, or do nothing with the data.

To clarify, using your type above, I can't do

match n with
    Int(i) -> print_int i
    | _ -> print_int some_data_from_n

Remember, all of my structures have many more than 1 piece of data.  A
class inheritance really is the best way to model the data structure, I
just want to be able to pattern match on it.

katre

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