Fix to issue #1072: decimal separator in lists should respect decimals setting.

stack/maximaparser/MP_classes.php

@@ -1488,7 +1488,7 @@ class MP_List extends MP_Node {
             return $indent . '[' . implode(', ', $ar) . ']';
         }
 
-        return '[' . implode(',', $ar) . ']';
+        return '[' . implode($sep, $ar) . ']';
     }
 
     public function replace($node, $with) {

tests/ast_container_test.php

@@ -1027,4 +1027,21 @@ class ast_container_test extends qtype_stack_testcase {
         $this->assertEquals($t3['last-seen'], false);
 
     }
+
+    public function test_teacher_answer_decimals() {
+        // This tests the functions which generate "The teacher's answer is".
+        $s = '{4.4,4}';
+        $at1 = stack_ast_container::make_from_teacher_source($s, '', new stack_cas_security());
+        $at1->set_nounify(0);
+        $this->assertTrue($at1->get_valid());
+        $this->assertEquals('', $at1->get_errors());
+        $this->assertEquals($at1->get_inputform(true, 0, true, ','), '{4,4;4}');
+
+        $s = '[4.4,4]';
+        $at1 = stack_ast_container::make_from_teacher_source($s, '', new stack_cas_security());
+        $at1->set_nounify(0);
+        $this->assertTrue($at1->get_valid());
+        $this->assertEquals('', $at1->get_errors());
+        $this->assertEquals($at1->get_inputform(true, 0, true, ','), '[4,4;4]');
+    }
 }