From 8f1ead168558dac9cf4c10e269f568e15b5f8faf Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?John=20Ankarstr=C3=B6m?= <john@ankarstrom.se>
Date: Fri, 15 Jul 2022 13:13:50 +0200
Subject: Add support for Prolog exceptions.

---
 c/common.cpp |  3 ++-
 c/defs.h     | 41 +++++++++++++++++++++++++++++++++++++----
 c/pl.cpp     | 39 +++++++++++++++++++++++++++++++++++----
 3 files changed, 74 insertions(+), 9 deletions(-)

(limited to 'c')

diff --git a/c/common.cpp b/c/common.cpp
index 89cc426..dd84742 100644
--- a/c/common.cpp
+++ b/c/common.cpp
@@ -31,7 +31,8 @@ TCHAR *TszFromSz(const char *sz, int iCp)
 
 Library::Library(const TCHAR *tszLibrary)
 {
-	if (!(m_hModule = LoadLibrary(tszLibrary)))
+	m_hModule = LoadLibrary(tszLibrary);
+	if (!m_hModule)
 		throw std::invalid_argument("Library not found.");
 }
 
diff --git a/c/defs.h b/c/defs.h
index c8d76b3..5a6a25a 100644
--- a/c/defs.h
+++ b/c/defs.h
@@ -66,8 +66,19 @@ struct DataListView : public ListView
 };
 
 /* pl.cpp */
-int Pl(const char *, const char *);
+int Plx(const char *, const char *);
+struct Query
+{
+	Query(module_t ctx, predicate_t p, term_t t0);
+	~Query();
+	int Cut();
+	int Close();
+	int NextSolution();
+private:
+	qid_t m_q;
+};
 
+/* Polymorphic aliases for PL_put_*, PL_get_*. */
 inline int PlPut(term_t t, int x) { return PL_put_integer(t, x); }
 inline int PlPut(term_t t, long x) { return PL_put_integer(t, x); }
 inline int PlPut(term_t t, long long x) { return PL_put_integer(t, x); }
@@ -92,6 +103,7 @@ inline int PlGet(term_t t, long long *x) { return PL_get_int64(t, x); }
 inline int PlGet(term_t t, atom_t *x) { return PL_get_atom(t, x); }
 inline int PlGet(term_t t, char **x) { return PL_get_atom_chars(t, x); }
 
+/* Helper templates for Plx, Pl. */
 template <typename T>
 int PlPutv(term_t t, T arg) { return PlPut(t, arg); }
 template <typename T, typename ...R>
@@ -104,18 +116,39 @@ template <typename T>
 int Countv(int i, T arg) { return i+1; }
 template <typename T, typename ...R>
 int Countv(int i, T arg, R... rest) { return Countv(i+1, rest...); }
+
+/* Call Prolog predicate, propagating Prolog exceptions. */
 template <typename ...T>
-int Pl(const char *szMod, const char *szPred, T... args)
+int Plx(const char *szMod, const char *szPred, T... args)
 {
 	int iArity = Countv(0, args...);
 	term_t t = PL_new_term_refs(iArity);
 	if (!PlPutv(t, args...)) return 0;
-	if (!PL_call_predicate(NULL, PL_Q_CATCH_EXCEPTION, PL_predicate(szPred, iArity, szMod), t))
-		return 0;
+	Query q(NULL, PL_predicate(szPred, iArity, szMod), t);
+	if (!q.NextSolution()) return 0;
 	if (!PlGetv(t, args...)) return 0;
 	return 1;
 }
 
+/* Call Prolog predicate, ignoring Prolog exceptions. */
+inline int Pl(const char *szMod, const char *szPred)
+{
+	try {
+		return Plx(szMod, szPred);
+	} catch (term_t &t) {
+		return 0;
+	}
+}
+template <typename ...T>
+int Pl(const char *szMod, const char *szPred, T... args)
+{
+	try {
+		return Plx(szMod, szPred, args...);
+	} catch (term_t &t) {
+		return 0;
+	}
+}
+
 /* defs.h */
 #ifdef UNICODE
 #define WA "W"
diff --git a/c/pl.cpp b/c/pl.cpp
index 3172090..1fbc4e7 100644
--- a/c/pl.cpp
+++ b/c/pl.cpp
@@ -1,9 +1,40 @@
 #include <SWI-Prolog.h>
+#include "defs.h"
 
-int Pl(const char *szMod, const char *szPred)
+Query::Query(module_t ctx, predicate_t p, term_t t0)
+{
+	m_q = PL_open_query(ctx, PL_Q_CATCH_EXCEPTION, p, t0);
+}
+
+Query::~Query()
+{
+	PL_cut_query(m_q);
+}
+
+int Query::Cut()
+{
+	if (PL_cut_query(m_q)) return 1;
+	if (term_t t = PL_exception(m_q)) throw t;
+	return 0;
+}
+
+int Query::Close()
+{
+	if (PL_close_query(m_q)) return 1;
+	if (term_t t = PL_exception(m_q)) throw t;
+	return 0;
+}
+
+int Query::NextSolution()
+{
+	if (PL_next_solution(m_q)) return 1;
+	if (term_t t = PL_exception(m_q)) throw t;
+	return 0;
+}
+
+int Plx(const char *szMod, const char *szPred)
 {
 	term_t t = PL_new_term_refs(0);
-	if (!PL_call_predicate(NULL, PL_Q_CATCH_EXCEPTION, PL_predicate(szPred, 0, szMod), t))
-		return 0;
-	return 1;
+	Query q(NULL, PL_predicate(szPred, 0, szMod), t);
+	return q.NextSolution();
 }
-- 
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