python
import ply.lex as lex
tokens = (
'NUMBER',
'PLUS',
'TIMES',
)
def t_NUMBER(t):
r'\d+'
t.value = int(t.value)
return t
t_PLUS = r'\+'
t_TIMES = r'\*'
t_ignore = ' \t'
def t_error(t):
print(f"Unexpected character: {t.value[0]}")
t.lexer.skip(1)
lexer = lex.lex()
python
import ply.yacc as yacc
def p_expression_plus(p):
'expression : expression PLUS expression'
p[0] = p[1] + p[3]
def p_expression_times(p):
'expression : expression TIMES expression'
p[0] = p[1] * p[3]
def p_expression_number(p):
'expression : NUMBER'
p[0] = p[1]
def p_error(p):
print("Syntax error")
parser = yacc.yacc()
python
while True:
try:
s = input('>>> ')
except EOFError:
break
if not s:
continue
result = parser.parse(s)
print(result)
