Re: Singleton variable in branch: right warning message?

On Mon, Mar 17, 2014 at 6:32 AM, Parker Jones <[email protected]> wrote:

> This code gives the warning "Singleton variable in branch: A", but
> shouldn't it be a regular singleton warning?
>
>
> p(X) :-
>     (X > 0 ->
>         A=1
>         ;
>         A=0
>     ).


It's not a regular singleton warning because the variable A appears twice
in this clause.  This code has two branches: X > 0 and X =< 0.  Simplifying
you have roughly:

P(X) :- A=1. % when X > 0
P(X) :- A=0. % when X =< 0

You can see that A is a singleton (appears only once) in each of those
clauses (each representing a branch).

By adding write(A), you add a second occurrence of the variable A to each
branch, so it's no longer a singleton.

-- 
Michael
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