117 lines
2.4 KiB
Python
117 lines
2.4 KiB
Python
# -----------------------------------------------------------------------------
|
|
# calc.py
|
|
#
|
|
# A simple calculator with variables. This is from O'Reilly's
|
|
# "Lex and Yacc", p. 63.
|
|
#
|
|
# This example uses unicode strings for tokens, docstrings, and input.
|
|
# -----------------------------------------------------------------------------
|
|
|
|
import sys
|
|
sys.path.insert(0,"../..")
|
|
|
|
tokens = (
|
|
'NAME','NUMBER',
|
|
'PLUS','MINUS','TIMES','DIVIDE','EQUALS',
|
|
'LPAREN','RPAREN',
|
|
)
|
|
|
|
# Tokens
|
|
|
|
t_PLUS = ur'\+'
|
|
t_MINUS = ur'-'
|
|
t_TIMES = ur'\*'
|
|
t_DIVIDE = ur'/'
|
|
t_EQUALS = ur'='
|
|
t_LPAREN = ur'\('
|
|
t_RPAREN = ur'\)'
|
|
t_NAME = ur'[a-zA-Z_][a-zA-Z0-9_]*'
|
|
|
|
def t_NUMBER(t):
|
|
ur'\d+'
|
|
try:
|
|
t.value = int(t.value)
|
|
except ValueError:
|
|
print "Integer value too large", t.value
|
|
t.value = 0
|
|
return t
|
|
|
|
t_ignore = u" \t"
|
|
|
|
def t_newline(t):
|
|
ur'\n+'
|
|
t.lexer.lineno += t.value.count("\n")
|
|
|
|
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','PLUS','MINUS'),
|
|
('left','TIMES','DIVIDE'),
|
|
('right','UMINUS'),
|
|
)
|
|
|
|
# dictionary of names
|
|
names = { }
|
|
|
|
def p_statement_assign(p):
|
|
'statement : NAME EQUALS expression'
|
|
names[p[1]] = p[3]
|
|
|
|
def p_statement_expr(p):
|
|
'statement : expression'
|
|
print p[1]
|
|
|
|
def p_expression_binop(p):
|
|
'''expression : expression PLUS expression
|
|
| expression MINUS expression
|
|
| expression TIMES expression
|
|
| expression DIVIDE expression'''
|
|
if p[2] == u'+' : p[0] = p[1] + p[3]
|
|
elif p[2] == u'-': p[0] = p[1] - p[3]
|
|
elif p[2] == u'*': p[0] = p[1] * p[3]
|
|
elif p[2] == u'/': p[0] = p[1] / p[3]
|
|
|
|
def p_expression_uminus(p):
|
|
'expression : MINUS expression %prec UMINUS'
|
|
p[0] = -p[2]
|
|
|
|
def p_expression_group(p):
|
|
'expression : LPAREN expression RPAREN'
|
|
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(unicode(s))
|