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|
# -----------------------------------------------------------------------------
# calc.py
#
# A simple calculator with variables. Asks the user for more input and
# demonstrates the use of the t_eof() rule.
# -----------------------------------------------------------------------------
import sys
sys.path.insert(0, "../..")
if sys.version_info[0] >= 3:
raw_input = input
tokens = (
'NAME', 'NUMBER',
)
literals = ['=', '+', '-', '*', '/', '(', ')']
# Tokens
t_NAME = r'[a-zA-Z_][a-zA-Z0-9_]*'
def t_NUMBER(t):
r'\d+'
t.value = int(t.value)
return t
t_ignore = " \t"
def t_newline(t):
r'\n+'
t.lexer.lineno += t.value.count("\n")
def t_eof(t):
more = raw_input('... ')
if more:
t.lexer.input(more + '\n')
return t.lexer.token()
else:
return None
def t_error(t):
print("Illegal character '%s'" % t.value[0])
t.lexer.skip(1)
# Build the lexer
import ply.lex as lex
lex.lex()
# Parsing rules
precedence = (
('left', '+', '-'),
('left', '*', '/'),
('right', 'UMINUS'),
)
# dictionary of names
names = {}
def p_statement_assign(p):
'statement : NAME "=" expression'
names[p[1]] = p[3]
def p_statement_expr(p):
'statement : expression'
print(p[1])
def p_expression_binop(p):
'''expression : expression '+' expression
| expression '-' expression
| expression '*' expression
| expression '/' expression'''
if p[2] == '+':
p[0] = p[1] + p[3]
elif p[2] == '-':
p[0] = p[1] - p[3]
elif p[2] == '*':
p[0] = p[1] * p[3]
elif p[2] == '/':
p[0] = p[1] / p[3]
def p_expression_uminus(p):
"expression : '-' expression %prec UMINUS"
p[0] = -p[2]
def p_expression_group(p):
"expression : '(' expression ')'"
p[0] = p[2]
def p_expression_number(p):
"expression : NUMBER"
p[0] = p[1]
def p_expression_name(p):
"expression : NAME"
try:
p[0] = names[p[1]]
except LookupError:
print("Undefined name '%s'" % p[1])
p[0] = 0
def p_error(p):
if p:
print("Syntax error at '%s'" % p.value)
else:
print("Syntax error at EOF")
import ply.yacc as yacc
yacc.yacc()
while 1:
try:
s = raw_input('calc > ')
except EOFError:
break
if not s:
continue
yacc.parse(s + '\n')
|
