Do not allow ambiguous datatype strings.

src/lua_term.c

@@ -179,7 +179,9 @@ static int l_new_iriref_rel (lua_State *L)
  * datatype has precedence. If both are nil, datatype is set to the default
  * (xsd:string).
  *
- * Data type can be either a namespace-prefixed or a fully qualified URI.
+ * Data type can be either a namespace-prefixed or a fully qualified URI. This
+ * must be specified with arg 4 (dtype_ns), set to `true` if the string passed
+ * is a namespace-prefixed URI. Volksdata cannot guess that.
  */
 static int l_new_lit (lua_State *L)
 {
@@ -187,17 +189,17 @@ static int l_new_lit (lua_State *L)
         *data = luaL_checkstring (L, 1),
         *dtype_str = lua_tostring (L, 2);
     const char *lang = lua_tostring (L, 3);
+    const bool dtype_ns = lua_toboolean (L, 4);
 
     VOLK_Term **tp = allocate_term (L);
     VOLK_Term *dtype;
 
     if (dtype_str) {
-        // TODO check memory leak.
-        dtype = VOLK_iriref_new_ns (dtype_str);
-        if (!dtype) dtype = VOLK_iriref_new (dtype_str);
+        dtype = dtype_ns ? VOLK_iriref_new_ns (dtype_str) :
+                VOLK_iriref_new (dtype_str);
         LUA_NLCHECK (dtype, "Error creating data type URI.");
         *tp = VOLK_literal_new (data, dtype);
-        LUA_NLCHECK (tp, "Error creating literal term.");
+        LUA_NLCHECK (*tp, "Error creating literal term.");
     }
     else if (lang) *tp = VOLK_lt_literal_new (data, (char *)lang);
     else *tp = VOLK_literal_new (data, NULL);