/// <summary>
/// Provide the next solution to the query. Prolog exceptions are mapped to C# exceptions.
/// </summary>
/// <returns>return true if successful and false if there are no (more) solutions.</returns>
/// <remarks>
/// <para>If the query is closed it will be opened. If the last solution was generated the query will be closed.</para>
/// <para>If an exception is thrown while parsing (open) the query the _qid is set to zero.</para>
/// </remarks>
/// <exception cref="PlException">Is thrown if <see href="http://gollem.science.uva.nl/SWI-Prolog/Manual/foreigninclude.html#PL_next_solution()">SWI-Prolog Manual PL_next_solution()</see> returns false </exception>
public bool NextSolution()
{
if (0 == _qid)
{
Check.Require(!string.IsNullOrEmpty(_name), "PlQuery.NextSolution() _name is required");
IntPtr p = LibPl.PL_predicate(_name, _av.Size, _module);
_qid = LibPl.PL_open_query((IntPtr)0, LibPl.PL_Q_CATCH_EXCEPTION, p, _av.A0);
}
int rval = LibPl.PL_next_solution(_qid);
if (0 == rval)
{ // error
uintptr_t ex; // term_t
if ((ex = LibPl.PL_exception(_qid)) > 0)
{
_qid = 0; // to avoid an AccessViolationException on Dispose. E.g. if the query is miss spelled.
var etmp = new PlException(new PlTerm(ex));
etmp.Throw();
}
}
if (rval <= 0)
{
Free(false);
}
return(rval > 0);
}
private void CheckForException()
{
uint ex = libpl.PL_exception(_qid); // term_t
if (ex > 0)
{
PlTerm exceptionTerm = new PlTerm(ex);
PlException etmp = new PlException(exceptionTerm);
_qid = 0; // to avoid an AccessViolationException on Dispose. E.g. if the query is miss spelled.
etmp.Throw();
}
}