Re: [pure-lang-users] Swapping Symbols and Integers

[Albert G. <Dr....@t-...>]

Hi David,

David Baird wrote:
> So, I thought maybe I could create a rule like this:
> 
>     A:Symbol * B:Integer = B * A;
>     // and maybe some more rules for associativity/commutivity

There's not type for symbols in either Pure or Q, and in Q the type of 
integers is named Int (section 8.2 of the manual), int and bigint in 
Pure. To check for free variable symbols, there's the isvar predicate, 
described in Section 10.8 of the manual (varp in Pure, see primitives.pure).

So something like this should do the job in Pure:

a*b::int = b*a if varp a;
x*a*b::int = x*b*a if varp a;

(In addition, you'll probably need some associativity rules to make this 
work in the general case.)

HTH,
Albert

-- 
Dr. Albert Gr"af
Dept. of Music-Informatics, University of Mainz, Germany
Email:  Dr....@t-..., ag...@mu...
WWW:    http://www.musikinformatik.uni-mainz.de/ag