[LANGUAGE] Nested functions (hedyorg#4280)

**Description**

**Adds** exception for nested functions
**Fixes** hedyorg#4240

exceptions.py

@@ -279,3 +279,8 @@ def __init__(self, command, level, line_number):
                          command=command,
                          level=level,
                          line_number=line_number)
+
+
+class NestedFunctionException(HedyException):
+    def __init__(self):
+        super().__init__('Nested Function')

grammars/level11-Additions.lark

@@ -1,11 +1,13 @@
-command:+= for_loop | call | define
+command:+= for_loop | call | error_nested_define
 
 //new : for loop
 for_loop: _FOR var _IN _RANGE (INT | var_access) _TO (INT | var_access) _EOL (_SPACE command) (_EOL _SPACE command)*  _EOL? _END_BLOCK
 
 // FUNCTIONS ======================================== =============================
 // check line 1: command:+= call | define
+_non_empty_program: _EOL* (define | command | error_invalid) _SPACE* (_EOL+ (define | command) _SPACE*)* _EOL* //lines may end on spaces and might be separated by many newlines
 define: _DEFINE function_name _EOL (_SPACE command) (_EOL _SPACE command)* _EOL? _END_BLOCK
 call: _CALL function_name
 function_name: NAME -> text
+error_nested_define: define
 // ================================================================================

hedy.py

@@ -1216,6 +1216,10 @@ def error_ifpressed_missing_else(self, meta, args):
         error = InvalidInfo('ifpressed missing else', arguments=[str(args[0])], line=meta.line, column=meta.column)
         return False, error, meta
 
+    def error_nested_define(self, meta, args):
+        error = InvalidInfo('nested function', arguments=[str(args[0])], line=meta.line, column=meta.column)
+        return False, error, meta
+
     # other rules are inherited from Filter
 
 
@@ -3018,6 +3022,8 @@ def is_program_valid(program_root, input_string, level, lang):
         elif invalid_info.error_type == 'ifpressed missing else':
             raise exceptions.MissingElseForPressitException(
                 command='ifpressed_else', level=level, line_number=invalid_info.line)
+        elif invalid_info.error_type == 'nested function':
+            raise exceptions.NestedFunctionException()
         else:
             invalid_command = invalid_info.command
             closest = closest_command(invalid_command, get_suggestions_for_language(lang, level))

tests/test_level/test_level_11.py

@@ -389,3 +389,16 @@ def simple_function():
             expected=expected,
             output=output,
         )
+
+    def test_nested_functions(self):
+        code = textwrap.dedent("""\
+        define simple_function
+            define nested_function
+                print 1
+        call simple_function""")
+
+        self.multi_level_tester(
+            code=code,
+            exception=hedy.exceptions.NestedFunctionException,
+            max_level=16,
+        )

tests/test_level/test_level_17.py

@@ -536,6 +536,15 @@ def test_pressed_elif(self):
 
         self.single_level_tester(code=code, expected=expected)
 
+    def test_nested_functions(self):
+        code = textwrap.dedent("""\
+        define simple_function:
+            define nested_function:
+                print 1
+        call simple_function""")
+
+        self.single_level_tester(code=code, exception=hedy.exceptions.NestedFunctionException)
+
     def test_source_map(self):
         code = textwrap.dedent("""\
         for i in range 1 to 10:

tests/test_level/test_level_18.py

@@ -334,3 +334,12 @@ def test_if_button_is_pressed_print(self):
             # End of PyGame Event Handler""")
 
         self.single_level_tester(code=code, expected=expected)
+
+    def test_nested_functions(self):
+        code = textwrap.dedent("""\
+        def simple_function():
+            def nested_function():
+                print(1)
+        simple_function()""")
+
+        self.single_level_tester(code=code, exception=hedy.exceptions.NestedFunctionException)