bugfix for print names in the C runtime and expose the functionality from Java

src/runtime/c/pgf/pgf.c

@@ -191,9 +191,7 @@ PGF_API GuString
 pgf_print_name(PgfConcr* concr, PgfCId id)
 {
 	PgfCId name =
-		gu_map_get(concr->printnames, id, PgfCId);
+		gu_map_get(concr->printnames, id, GuString);
-	if (*name == 0)
-		name = id;
 	return name;
 }
 

src/runtime/c/pgf/reader.c

@@ -565,7 +565,7 @@ pgf_read_abstract(PgfReader* rdr, PgfAbstr* abstract)
 static PgfCIdMap*
 pgf_read_printnames(PgfReader* rdr)
 {
-	PgfCIdMap* printnames = gu_new_string_map(GuString, &"", rdr->opool);
+	PgfCIdMap* printnames = gu_new_string_map(GuString, &gu_null_struct, rdr->opool);
 
 	size_t len = pgf_read_len(rdr);
 	gu_return_on_exn(rdr->err, NULL);

src/runtime/java/jpgf.c

@@ -1146,6 +1146,19 @@ Java_org_grammaticalframework_pgf_Concr_hasLinearization(JNIEnv* env, jobject se
 	return res;
 }
 
+JNIEXPORT jstring JNICALL
+Java_org_grammaticalframework_pgf_Concr_getPrintName(JNIEnv* env, jobject self, jstring jid)
+{
+	PgfConcr* concr = get_ref(env, self);
+	GuPool* tmp_pool = gu_local_pool();
+	PgfCId id = j2gu_string(env, jid, tmp_pool);
+	GuString name = pgf_print_name(concr, id);
+	jstring jname = (name == NULL) ? NULL : gu2j_string(env, name);
+	gu_pool_free(tmp_pool);
+
+	return jname;
+}
+
 JNIEXPORT jlong JNICALL
 Java_org_grammaticalframework_pgf_Pool_alloc(JNIEnv* env, jclass clazz)
 {

src/runtime/java/org/grammaticalframework/pgf/Concr.java

@@ -79,6 +79,10 @@ public class Concr {
 	 */
 	public native boolean hasLinearization(String fun);
 
+	/** returns the print name for that function or category.
+	 */
+	public native String getPrintName(String id);
+
 	/** If the concrete syntaxes in the grammar are stored in external
 	 * files then this method can be used to load the current syntax
 	 * in memory.

src/runtime/python/pypgf.c

@@ -1303,11 +1303,15 @@ Concr_init(ConcrObject *self, PyObject *args, PyObject *kwds)
 static PyObject*
 Concr_printName(ConcrObject* self, PyObject *args)
 {
-	GuString name;
+	GuString id;
-    if (!PyArg_ParseTuple(args, "s", &name))
+    if (!PyArg_ParseTuple(args, "s", &id))
         return NULL;
 
-	return PyString_FromString(pgf_print_name(self->concr, name));
+	GuString name = pgf_print_name(self->concr, id);
+	if (name == NULL)
+		Py_RETURN_NONE;
+
+	return PyString_FromString(name);
 }
 
 #if (    (PY_VERSION_HEX <  0x02070000) \