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From: mandel@forwiss.uni-passau.de (Luis Mandel)
Newsgroups: comp.compilers
Subject: Enumerated data types
Keywords: C, Pascal, design
Message-ID: <1990Aug23.134826.2865@forwiss.uni-passau.de>
Date: 23 Aug 90 13:48:26 GMT
Sender: compilers-sender@esegue.segue.boston.ma.us
Reply-To: mandel@forwiss.uni-passau.de (Luis Mandel)
Organization: University of Passau, W-Germany
Lines: 48
Approved: compilers@esegue.segue.boston.ma.us

Hello world,

I'm studing types, in particular enumerated data types of programming
languages. For example using Pascal enumerated data types, we can write
the following:

type
	car_colours = (red, blue, brown, black);

and also we obtain pred, suc and ord as associated functions to the new
data type:

		 suc(red) = blue        and so on.

Then we can't define another enumerated data type that involves the
tokens red, blue, brown or black, because of these functions pred and
suc. For example, if it were possible to write

type 
    bike_colours = (orange, red, green, white);

it were an ambiguity with suc(red) because there are two possibilities.
The same is with functions pre and ord.

Now my question is: anybody knows if there are languages that allows
anything like

	car_colours = (red, blue, brown, black);
    bike_colours = (orange, red, green, white);

and have these functions defined with an extra parameter, for example:

	  suc (car_colour, red) = blue
	  suc (bike_colour, red) = green

Are there problems with this definition of enumerated data types? 
Could be there difficulties trying to specify the semantics of suc,
pred and ord?, Any suggestion?

Thanks in advance, Luis  (mandel@forwiss.uni-passau.de)

--
Luis Mandel                                mandel@forwiss.uni-passau.de
[I'd think that if you always qualified your names, you might as well
call them car_colour_red and bike_colour_red. -John]
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