def parse_in_stmt():
'''
解析输入语句
'''
new_node = TreeNode('INSTMT')
new_node.line = tokens[tokens_index].pos[0]
check_next_token('in')
check_next_token('(')
new_node.add_child(parse_var())
check_next_token(')')
check_next_token(';')
return new_node
def parse_while_stmt():
'''
解析while语句
'''
node = TreeNode('WHILESTMT')
node.line = tokens[tokens_index].pos[0]
check_next_token('while')
check_next_token('(')
node.add_child(parse_condition())
check_next_token(')')
temp = parse_stmt()
if temp: node.add_child(temp)
return node if temp is not None else None
def parse(filename):
'''
语法分析主控程序，调用词法分析后，使用递归下降分析方法，不断进行语法分析，直至到tokens用完
:param filename:
:return:
'''
lexer(filename)
tokens.append(Token('END', 'END', None))
roots = TreeNode('root')
while tokens_index < len(tokens) - 1:
result = parse_stmt()
if result: roots.add_child(result)
tokens.pop(-1)
return roots
def parse_expr():
'''
解析表达式
'''
node = TreeNode('EXPR')
node.line = tokens[tokens_index].pos[0]
if get_next_token().name == '-':
node.add_child(check_next_token('-'))
node.add_child(parse_expr())
else:
node.add_child(parse_term())
while get_next_token().name in ['+', '-']:
node.add_child(check_next_token(get_next_token().name))
node.add_child(parse_term())
return node
def parse_cond():
'''
解析单个条件布尔项
'''
cond_node = TreeNode('COND')
cond_node.line = tokens[tokens_index].pos[0]
if get_next_token().name == '!':
cond_node.add_child(check_next_token('!'))
check_next_token('(')
cond_node.add_child(parse_cond())
check_next_token(')')
else:
cond_node.add_child(parse_expr())
cond_node.add_child(parse_compare())
cond_node.add_child(parse_expr())
return cond_node
def parse_block():
'''
解析语句块
'''
new_node = TreeNode('BLOCK')
new_node.line = tokens[tokens_index].pos[0]
leftbrace = get_next_token()
check_next_token('{')
while get_next_token().name != 'END' and get_next_token().name != '}':
stmt = parse_stmt()
if stmt: new_node.add_child(stmt)
if get_next_token().name == 'END':
raise ParseException("Not matched closed } for { at line %d" %
leftbrace.pos[0])
check_next_token('}')
return new_node
def parse_condition():
'''
解析整个条件布尔值
'''
condition_node = TreeNode('CONDITION')
condition_node.line = tokens[tokens_index].pos[0]
if get_next_token().name == '!':
condition_node.add_child(check_next_token('!'))
check_next_token('(')
condition_node.add_child(parse_condition())
check_next_token(')')
else:
condition_node.add_child(parse_cond())
while get_next_token().name in ['&&', '||']:
condition_node.add_child(check_next_token(get_next_token().name))
condition_node.add_child(parse_cond())
return condition_node
def parse_out_stmt():
'''
解析输出语句
'''
new_node = TreeNode('OUTSTMT')
new_node.line = tokens[tokens_index].pos[0]
check_next_token('out')
check_next_token('(')
token = get_next_token()
if token.type == 'STR':
new_node.add_child(parse_str())
else:
new_node.add_child(parse_expr())
check_next_token(')')
check_next_token(';')
return new_node
def parse_var():
'''
解析变量，包括标识符及数组元素
'''
token = get_next_token()
node = TreeNode('VAR')
node.line = tokens[tokens_index].pos[0]
if token.type == 'ID':
node.add_child(parse_id())
next_token = get_next_token()
if next_token.name == '[':
check_next_token('[')
node.add_child(parse_expr())
check_next_token(']')
return node
else:
raise ParseException('line %d: token should be a identifier' %
token.pos[0])
def parse_decl_stmt():
'''
解析声明语句
'''
type_token = get_next_token()
decl_node = TreeNode('VARDECL')
type_node = TreeNode('TYPE')
decl_node.line = tokens[tokens_index].pos[0]
type_node.line = tokens[tokens_index].pos[0]
decl_node.add_child(type_node)
type_node.add_child(check_next_token(type_token.name))
next_token = get_next_token()
if next_token.name == '[': #判断声明是否为数组
check_next_token('[')
num_token = get_next_token()
if num_token.type != 'NUM' or '.' in num_token.name: #声明数组长度时需为正整数
raise ParseException(
'Line %d: length of array should be a positive constant number'
% num_token.pos[0])
num_node = TreeNode('NUM')
num_node.line = tokens[tokens_index].pos[0]
num_node.value = num_token.name
type_node.add_child(num_node)
skip_next_token()
check_next_token(']')
id = parse_id()
decl_node.add_child(id)
next_name = get_next_token().name
assfunc = parse_str if type_token.name == 'string' else parse_expr
while next_name in [',', '=']:
if next_name == '=':
check_next_token('=')
id.add_child(assfunc())
else:
check_next_token(',')
id = parse_id()
decl_node.add_child(id)
next_name = get_next_token().name
check_next_token(';')
return decl_node
def parse_term():
'''
解析表达式中单个项
'''
node = TreeNode('TERM')
node.line = tokens[tokens_index].pos[0]
node.add_child(parse_factor())
while get_next_token().name in ['*', '/']:
node.add_child(check_next_token(get_next_token().name))
node.add_child(parse_factor())
return node
def parse_assign_stmt():
'''
解析赋值语句
'''
node = TreeNode('ASSIGNSTMT')
node.line = tokens[tokens_index].pos[0]
node.add_child(parse_var())
check_next_token('=')
token = get_next_token()
if token.type == 'STR':
node.add_child(parse_str())
else:
node.add_child(parse_expr())
check_next_token(';')
return node
def parse_if_stmt():
'''
解析if语句
'''
node = TreeNode('IFSTMT')
node.line = tokens[tokens_index].pos[0]
check_next_token('if')
check_next_token('(')
node.add_child(parse_condition())
check_next_token(')')
temp = parse_stmt()
if temp: node.add_child(temp)
if get_next_token().name == 'else':
check_next_token('else')
temp = parse_stmt()
if temp: node.add_child(temp)
return node if temp is not None else None
def parse_factor():
'''
解析项中单个因子
'''
node = TreeNode('FACTOR')
node.line = tokens[tokens_index].pos[0]
token = get_next_token()
if token.type == 'NUM':
rnode = TreeNode('NUM')
rnode.line = tokens[tokens_index].pos[0]
rnode.value = token.name
node.add_child(rnode)
skip_next_token()
elif token.name == '(':
check_next_token('(')
node.add_child(parse_expr())
check_next_token(')')
else:
node.add_child(parse_var())
return node