[mercury-users] Working with exported types

[Peter Schachte]

On Thu, Jul 27, 2006 at 03:14:40PM +1000, Jonathan Morgan wrote:
> Say I have an enum something like the following.
> 
> :- type my_enum --->
>    value1 ;
>    value2 ;
>    value3.
> 
> If I am working with such a type in foreign code there are a couple of
> ways I could do it.
> 
> 1. Assume that value1, value2 and value3 map to the values 0, 1 and 2,
> and then just test against or assign these values.  Efficient, but may
> be broken by change in representation.
> 
> 2. Export Mercury predicates that work on this type, and use these
> exported predicate exclusively.

If you're only worried about enums, how about writing a little mercury
program to read the mercury source file and generate a C file
containing an enum declaration like

	enum my_enum { value1, value2, value3 };

or maybe

	typedef enum { value1, value2, value3 } my_enum;

Then use a little Makefile magic to keep this file up to date when you
change your mercury source file.

Better still:  build this into the compiler, which knows for sure
which values are given to the enum constants.

-- 
Peter Schachte              It has become appallingly obvious that our
schachte at cs.mu.OZ.AU        technology has exceeded our humanity.
www.cs.mu.oz.au/~schachte/      -- Albert Einstein 
Phone: +61 3 8344 1338      
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