[LANGUAGE] Adds new exception to catch the use of at in level 16+ (h…

…edyorg#3831)

**Description**
Fixes issue hedyorg#3800 so now if a student attempts to use 'at random' in either a print statement or an expression or just by itself (fruit at random), an informative message will tell them to use 'list_name[random]' instead. 



**How to test**

Added some test cases to test for "print fruits at random," "x = fruits at random," and "x is fruits at random"

**Checklist**
Done? Check if you have it all in place using this list:*
  
- [ ] Contains one of the PR categories in the name
- [ ] Describes changes in the format above
- [ ] Links to an existing issue or discussion 
- [ ] Has a "How to test" section

If you're unsure about any of these, don't hesitate to ask. We're here to help!

content/error-messages.txt

@@ -44,4 +44,5 @@ gettext('number')
 gettext('integer')
 gettext('float')
 gettext('list')
-gettext('input')
+gettext('input')
+gettext('Invalid At Command')

exceptions.py

@@ -174,6 +174,14 @@ def __init__(self, command, level, line_number):
                          line_number=line_number)
 
 
+class InvalidAtCommandException(HedyException):
+    def __init__(self, command, level, line_number):
+        super().__init__('Invalid At Command',
+                         command=command,
+                         level=level,
+                         line_number=line_number)
+
+
 class IncompleteRepeatException(HedyException):
     def __init__(self, command, level, line_number):
         super().__init__('Incomplete Repeat',

grammars/level16-Additions.lark

@@ -1,9 +1,18 @@
 // adds list access with numbers and brackets
-command:+= change_list_item
 // TODO for tomorrow: this stills needs tests in level 16 for > and !=
+command:+= change_list_item
+
 ?comparison_arg: var_access | text_in_quotes | NUMBER | list_access
 
 ?atom: NUMBER | _MINUS NUMBER | var_access | list_access | text_in_quotes
 list_access: var_access _LEFT_SQUARE_BRACKET (INT | random | var_access) _RIGHT_SQUARE_BRACKET
 change_list_item: var_access _LEFT_SQUARE_BRACKET (INT | var_access) _RIGHT_SQUARE_BRACKET _EQUALS (var_access | textwithoutspaces)
 assign_list: var (_IS | _EQUALS) _LEFT_SQUARE_BRACKET ((quoted_text | INT) (_COMMA (quoted_text | INT))*)? _RIGHT_SQUARE_BRACKET
+
+error_list_access_at: var_access _AT (INT | random)
+
+_print_argument: (_SPACE | quoted_text | list_access | error_list_access_at | expression | print_expression)*
+assign: var (_IS| _EQUALS) (list_access | error_list_access_at | atom | expression)
+error_print_no_quotes: _PRINT (textwithoutspaces | list_access | error_list_access_at | var_access) (_SPACE (textwithoutspaces | list_access | var_access))*  -> error_print_nq
+sleep: _SLEEP (INT | list_access | error_list_access_at | var_access | expression)?
+turtle: _FORWARD ((NUMBER | list_access | error_list_access_at | textwithoutspaces | expression))? -> forward | _TURN ((NUMBER | list_access | error_list_access_at | textwithoutspaces | expression))? -> turn | _COLOR ((black | blue | brown | gray | green | orange | pink | purple | red | white | yellow | list_access | error_list_access_at | textwithoutspaces))? -> color

hedy.py

@@ -1167,6 +1167,9 @@ def error_text_no_print(self, meta, args):
         error = InvalidInfo('lonely text', arguments=[str(args[0])], line=meta.line, column=meta.column)
         return False, error, meta
 
+    def error_list_access_at(self, meta, args):
+        error = InvalidInfo('invalid at keyword', arguments=[str(args[0])], line=meta.line, column=meta.column)
+        return False, error, meta
     # other rules are inherited from Filter
 
 
@@ -2867,6 +2870,8 @@ def is_program_valid(program_root, input_string, level, lang):
             raise exceptions.UnsupportedFloatException(value=''.join(invalid_info.arguments))
         elif invalid_info.error_type == 'lonely text':
             raise exceptions.LonelyTextException(level=level, line_number=line)
+        elif invalid_info.error_type == 'invalid at keyword':
+            raise exceptions.InvalidAtCommandException(command='at', level=level, line_number=invalid_info.line)
         else:
             invalid_command = invalid_info.command
             closest = closest_command(invalid_command, get_suggestions_for_language(lang, level))

messages.pot

@@ -290,6 +290,9 @@ msgstr ""
 msgid "input"
 msgstr ""
 
+msgid "Invalid At Command"
+msgstr ""
+
 msgid "general"
 msgstr ""
 

tests/test_level/test_level_16.py

@@ -616,3 +616,10 @@ def test_if_pressed_with_list_and_for(self):
               break""")
 
         self.single_level_tester(code=code, expected=expected)
+
+    @parameterized.expand(['sleep', 'number is', 'print', 'forward', 'turn'])
+    def test_at_random_express(self, command):
+        code = textwrap.dedent(f"""\
+            numbers is [1, 2, 3]
+            {command} numbers at random""")
+        self.single_level_tester(code=code, exception=hedy.exceptions.InvalidAtCommandException)