Re: gprolog display incorrectly a ?

[Paulo Moura]

On 14/fev/2005, at 17:45, Michel Levy wrote:

> Let's suppose that the predicate a is defined by
> a(f(b),1).
> a(f(c),2).
> We execute the query
> ?- a(f(b),X).
> X = 1?
> Why Prolog display a ? although there are no remaining alternatives ?

Most Prolog compilers, including GNU Prolog, use first-argument 
indexing when compiling predicate clauses in order to speed-up query 
execution. This indexing mechanism (which usually is implemented using 
a hash table) can only help detecting query determinism based on the 
first argument.

Cheers,

Paulo


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Paulo Jorge Lopes de Moura
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