Merge branch 'dpbutter-fix-join'

Author: Kasper Peeters

core/pythoncdb/py_ex.cc

@@ -137,9 +137,17 @@ namespace cadabra {
 		auto ret = std::make_shared<Ex>("\\comma");
 
 		for(const Ex_ptr& ex: exs) {
-			auto loc = ret->append_child(ret->begin(), ex->begin());
-			if(*ex->begin()->name=="\\comma") 
-				ret->flatten_and_erase(loc);
+			// skip ex if empty
+			if (ex->size() > 0) {
+				auto loc = ret->append_child(ret->begin(), ex->begin());
+				if(*ex->begin()->name=="\\comma") 
+					ret->flatten_and_erase(loc);
+				}
+			}
+		// Note: ret could still \comma{} or \comma{x}
+		auto it = ret->begin();
+		if (ret->number_of_children(it) < 2) {
+			ret->flatten_and_erase(it);
 			}
 		return ret;
 		}

tests/programming.cdb

@@ -333,6 +333,15 @@ def test14():
     ex4= join(ex1, ex2, ex3)
     assert(ex4==${A,C,D,E}$)
     print("Test 14g passed")
+    ex1:= A;
+    ex4 = join(ex1, Ex(""))
+    assert(ex4==$A$)
+    print("Test 14h passed")
+    ex1:= A;
+    ex2:= \comma{};
+    ex4= join(ex1, ex2)
+    assert(ex4==$A$)
+    print("Test 14i passed")
 
 test14()