def 条件语句(self):
sub_tree = TreeNode('<条件语句>')
syntax_tree = None
if isinstance(self.token, Keyword) and self.token.value == 'if':
child_tree = TreeNode(self.token)
self.token = self.lexer.forward()
condition, ast_condition = self.条件()
child_tree.sublings.append(condition)
if isinstance(self.token, Keyword) and self.token.value == 'then':
child_tree.sublings.append(TreeNode(self.token))
self.token = self.lexer.forward()
statment, ast_true_stmt = self.语句()
child_tree.sublings.append(statment)
ast_false_stmt = SyntaxTree.EmptyStatement()
if isinstance(self.token, Keyword) and self.token.value == 'else':
child_tree.sublings.append(TreeNode(self.token))
self.token = self.lexer.forward()
statment, ast_false_stmt = self.语句()
child_tree.sublings.append(statment)
sub_tree.child = child_tree
syntax_tree = SyntaxTree.IfStatement(ast_condition, ast_true_stmt, false_stmt=ast_false_stmt)
return sub_tree, syntax_tree
else:
if self.lexer.hasnext():
statement = self.lexer.statement.split('\n')
pos_str = "{}\n{}".format(statement[self.lexer.line_index -1 ], " "*(self.lexer.character_index-2) )
pos_str += '^'
invalid_str = '"then" expected, get "{}" at line {}'.format(self.token.value, self.lexer.line_index)
raise SyntaxException("{}\n{}".format(invalid_str, pos_str))
else:
raise SyntaxException("{}".format('unexpected EOF!'))
else:
self.unexpected_error('if')
def 语句(self):
sub_tree = TreeNode('<语句>')
if isinstance(self.token, Identifier):
# assginment
child_tree, syntax_tree = self.赋值语句()
sub_tree.child = child_tree
# syntax_tree.print()
return sub_tree, syntax_tree
call_tab = {
'if':self.条件语句,
'while':self.当型循环语句,
'call':self.过程调用语句,
'read':self.读语句,
'write':self.写语句,
'begin':self.复合语句,
'repeat':self.重复语句,
}
if isinstance(self.token, Keyword) and self.token.value in call_tab:
# print("选择 {}".format(self.token.value))
child_tree, syntax_tree = call_tab[self.token.value]()
sub_tree.child = child_tree
return sub_tree, syntax_tree
else:
sub_tree.child = TreeNode("")
return sub_tree, SyntaxTree.EmptyStatement()