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#!/usr/bin/env python
# -----------------------------------------------------------------------------
# calc.py
#
# A simple calculator with variables. This is from O'Reilly's
# "Lex and Yacc", p. 63.
#
# Class-based example contributed to PLY by David McNab
# -----------------------------------------------------------------------------
import sys
sys.path.insert(0,"../..")
import readline
import ply.lex as lex
import ply.yacc as yacc
import os
class Parser:
"""
Base class for a lexer/parser that has the rules defined as methods
"""
tokens = ()
precedence = ()
def __init__(self, **kw):
self.debug = kw.get('debug', 0)
self.names = { }
try:
modname = os.path.split(os.path.splitext(__file__)[0])[1] + "_" + self.__class__.__name__
except:
modname = "parser"+"_"+self.__class__.__name__
self.debugfile = modname + ".dbg"
self.tabmodule = modname + "_" + "parsetab"
#print self.debugfile, self.tabmodule
# Build the lexer and parser
lex.lex(module=self, debug=self.debug)
yacc.yacc(module=self,
debug=self.debug,
debugfile=self.debugfile,
tabmodule=self.tabmodule)
def run(self):
while 1:
try:
s = raw_input('calc > ')
except EOFError:
break
if not s: continue
yacc.parse(s)
class Calc(Parser):
tokens = (
'NAME','NUMBER',
'PLUS','MINUS','EXP', 'TIMES','DIVIDE','EQUALS',
'LPAREN','RPAREN',
)
# Tokens
t_PLUS = r'\+'
t_MINUS = r'-'
t_EXP = r'\*\*'
t_TIMES = r'\*'
t_DIVIDE = r'/'
t_EQUALS = r'='
t_LPAREN = r'\('
t_RPAREN = r'\)'
t_NAME = r'[a-zA-Z_][a-zA-Z0-9_]*'
def t_NUMBER(self, t):
r'\d+'
try:
t.value = int(t.value)
except ValueError:
print "Integer value too large", t.value
t.value = 0
#print "parsed number %s" % repr(t.value)
return t
t_ignore = " \t"
def t_newline(self, t):
r'\n+'
t.lexer.lineno += t.value.count("\n")
def t_error(self, t):
print "Illegal character '%s'" % t.value[0]
t.lexer.skip(1)
# Parsing rules
precedence = (
('left','PLUS','MINUS'),
('left','TIMES','DIVIDE'),
('left', 'EXP'),
('right','UMINUS'),
)
def p_statement_assign(self, p):
'statement : NAME EQUALS expression'
self.names[p[1]] = p[3]
def p_statement_expr(self, p):
'statement : expression'
print p[1]
def p_expression_binop(self, p):
"""
expression : expression PLUS expression
| expression MINUS expression
| expression TIMES expression
| expression DIVIDE expression
| expression EXP expression
"""
#print [repr(p[i]) for i in range(0,4)]
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]
elif p[2] == '**': p[0] = p[1] ** p[3]
def p_expression_uminus(self, p):
'expression : MINUS expression %prec UMINUS'
p[0] = -p[2]
def p_expression_group(self, p):
'expression : LPAREN expression RPAREN'
p[0] = p[2]
def p_expression_number(self, p):
'expression : NUMBER'
p[0] = p[1]
def p_expression_name(self, p):
'expression : NAME'
try:
p[0] = self.names[p[1]]
except LookupError:
print "Undefined name '%s'" % p[1]
p[0] = 0
def p_error(self, p):
print "Syntax error at '%s'" % p.value
if __name__ == '__main__':
calc = Calc()
calc.run()
|
