[mercury-users] natural numbers

[Robert Bossy]

[ Tue, 24 Jul 2001 18:24:08 +1000 ] Robert Colvin <robert at svrc.uq.edu.au> -> mercury-users at cs.mu.OZ.AU

> Hi, I wanted to know what is/would be the usual way to define the natural
> numbers using successor notation in Mercury.  Preferably I would use this:
> 
> :- type nat ---> 0; s(nat).
> 
> but I get the error:
> 
> mercTranslate.m:471: Error: invalid RHS of type definition: 0 ; s(nat).
> 
> which I assume is from the use of `0'.  I will probably use eg. `e' in place of
> 0, unless there is something I'm missing...?

That's it.
Constructors must be valid atoms i.e. a word begining with a lowercase alphabetic character.

:- type nat ---> zero; s(nat).


However you can use quotes if you insist having the 0 constructor:

:- type nat ---> '0'; s(nat).

RB
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