/// <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="SwiPrologException">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), "PrologQuery.NextSolution() _name is required");
Contract.Requires(!string.IsNullOrEmpty(_name), "PrologQuery.NextSolution() _name is required");
IntPtr p = libswipl.PL_predicate(_name, _av.Size, _module);
var atom = libswipl.PL_new_atom_wchars(_module);
IntPtr m = libswipl.PL_new_module(atom);
libswipl.PL_unregister_atom(atom);
_qid = libswipl.PL_open_query(m /* was IntPtr.Zero */, libswipl.PL_Q_CATCH_EXCEPTION, p, _av.A0);
}
int rval = libswipl.PL_next_solution(_qid);
if (0 == rval)
{ // error
uintptr_t ex; // term_t
if ((ex = libswipl.PL_exception(_qid)) > 0)
{
_qid = 0; // to avoid an AccessViolationException on Dispose. E.g. if the query is mispelled.
var etmp = new SwiPrologException(new SwiPrologTerm(ex));
etmp.Throw();
}
}
if (rval <= 0)
{
Free(false);
}
return(rval > 0);
}
internal static void PL_close_query(uintptr_t qid)
{
if (IsValid)
{
SafeNativeMethods.PL_close_query(qid);
}
}
internal static void PL_close_foreign_frame(uintptr_t fid_t)
{
if (IsValid)
{
SafeNativeMethods.PL_close_foreign_frame(fid_t);
}
}
internal static string PL_atom_wchars(uintptr_t tAtom)
{
// see http://www.mycsharp.de/wbb2/thread.php?threadid=51100
int dummyLen = 0;
return(Marshal.PtrToStringUni(SafeNativeMethods.PL_atom_wchars(tAtom, ref dummyLen)));
}
/// <summary>called by Dispose</summary>
private void Free()
{
if (_fid > 0 && libswipl.PL_is_initialised(IntPtr.Zero, IntPtr.Zero) != 0)
{
libswipl.PL_close_foreign_frame(_fid);
}
_fid = 0;
}
internal static int PL_get_wchars(uintptr_t term, out string s, uint flags)
{
var dummyLen = 0;
var ps = IntPtr.Zero;
var iRet = SafeNativeMethods.PL_get_wchars(term, ref dummyLen, ref ps, flags);
s = Marshal.PtrToStringUni(ps);
return(iRet);
}
/// <summary>
/// Discards the query, but does not delete any of the data created by the query if discardData is false.
/// It just invalidate qid, allowing for a new PlQuery object in this context.
/// </summary>
/// <remarks>see <see href="http://gollem.science.uva.nl/SWI-Prolog/Manual/foreigninclude.html#PL_cut_query()"/></remarks>
/// <param name="discardData">if true all bindings of the query are destroyed</param>
private void Free(bool discardData)
{
if (_qid > 0 && libswipl.PL_is_initialised(IntPtr.Zero, IntPtr.Zero) != 0)
{
try
{
if (discardData)
{
// <"leider werden dann die gebundenen variablen der query wieder frei e.g. in PlCall(goal)"/>
// unfortunately this statement detaches the bound variables of the query e.g. in PlCall(goal)
libswipl.PL_close_query(_qid);
}
else
{
libswipl.PL_cut_query(_qid);
}
}
catch (AccessViolationException ex)
{
TraceAccessViolationException(ex);
}
}
_qid = 0;
}
internal static extern int PL_get_arg(int index, uintptr_t t, uintptr_t a);
internal static extern uintptr_t PL_exception(uintptr_t qid);
internal static extern int PL_unify(uintptr_t t1, uintptr_t t2);
internal static extern int PL_get_list(uintptr_t termL, uintptr_t termH, uintptr_t termT);
internal static extern int PL_unify_list(uintptr_t termL, uintptr_t termH, uintptr_t termT);
internal static extern int PL_is_number(uintptr_t term_t);
internal static extern int PL_wchars_to_term([In] string chars, uintptr_t term);
internal static extern int PL_cons_list(uintptr_t list, uintptr_t head, uintptr_t tail);
internal static extern int PL_is_list(uintptr_t term_t);
internal static extern int PL_is_atomic(uintptr_t term_t);
internal static extern void PL_cons_functor_v(uintptr_t term, uintptr_t functor_t, uintptr_t termA0);
internal static extern uintptr_t PL_copy_term_ref(uintptr_t term_t);
internal static extern uintptr_t PL_new_functor(uintptr_t atom, int a);
internal static extern int PL_unify_nil(uintptr_t term_t);
internal static extern int PL_is_variable(uintptr_t term_t);
internal static extern int PL_get_nil(uintptr_t term_t);
internal static extern int PL_is_string(uintptr_t term_t);
internal static extern int PL_unify_wchars(uintptr_t t1, int type, int len, string atom);
internal static extern int PL_is_integer(uintptr_t term_t);
internal static extern int PL_raise_exception(uintptr_t exceptionTerm);
internal static extern int PL_is_float(uintptr_t term_t);
internal static extern int PL_get_name_arity(uintptr_t t, ref uintptr_t name, ref int arity);
internal static extern int PL_is_compound(uintptr_t term_t);
