1#!/usr/bin/env python2.7
2
3# -----------------------------------------------------------------------------
4# calc.py
5#
6# A simple calculator with variables.   This is from O'Reilly's
7# "Lex and Yacc", p. 63.
8#
9# Class-based example contributed to PLY by David McNab
10# -----------------------------------------------------------------------------
11
12import sys
13sys.path.insert(0,"../..")
14
15if sys.version_info[0] >= 3:
16    raw_input = input
17
18import ply.lex as lex
19import ply.yacc as yacc
20import os
21
22class Parser:
23    """
24    Base class for a lexer/parser that has the rules defined as methods
25    """
26    tokens = ()
27    precedence = ()
28
29    def __init__(self, **kw):
30        self.debug = kw.get('debug', 0)
31        self.names = { }
32        try:
33            modname = os.path.split(os.path.splitext(__file__)[0])[1] + "_" + self.__class__.__name__
34        except:
35            modname = "parser"+"_"+self.__class__.__name__
36        self.debugfile = modname + ".dbg"
37        self.tabmodule = modname + "_" + "parsetab"
38        #print self.debugfile, self.tabmodule
39
40        # Build the lexer and parser
41        lex.lex(module=self, debug=self.debug)
42        yacc.yacc(module=self,
43                  debug=self.debug,
44                  debugfile=self.debugfile,
45                  tabmodule=self.tabmodule)
46
47    def run(self):
48        while 1:
49            try:
50                s = raw_input('calc > ')
51            except EOFError:
52                break
53            if not s: continue
54            yacc.parse(s)
55
56
57class Calc(Parser):
58
59    tokens = (
60        'NAME','NUMBER',
61        'PLUS','MINUS','EXP', 'TIMES','DIVIDE','EQUALS',
62        'LPAREN','RPAREN',
63        )
64
65    # Tokens
66
67    t_PLUS    = r'\+'
68    t_MINUS   = r'-'
69    t_EXP     = r'\*\*'
70    t_TIMES   = r'\*'
71    t_DIVIDE  = r'/'
72    t_EQUALS  = r'='
73    t_LPAREN  = r'\('
74    t_RPAREN  = r'\)'
75    t_NAME    = r'[a-zA-Z_][a-zA-Z0-9_]*'
76
77    def t_NUMBER(self, t):
78        r'\d+'
79        try:
80            t.value = int(t.value)
81        except ValueError:
82            print("Integer value too large %s" % t.value)
83            t.value = 0
84        #print "parsed number %s" % repr(t.value)
85        return t
86
87    t_ignore = " \t"
88
89    def t_newline(self, t):
90        r'\n+'
91        t.lexer.lineno += t.value.count("\n")
92
93    def t_error(self, t):
94        print("Illegal character '%s'" % t.value[0])
95        t.lexer.skip(1)
96
97    # Parsing rules
98
99    precedence = (
100        ('left','PLUS','MINUS'),
101        ('left','TIMES','DIVIDE'),
102        ('left', 'EXP'),
103        ('right','UMINUS'),
104        )
105
106    def p_statement_assign(self, p):
107        'statement : NAME EQUALS expression'
108        self.names[p[1]] = p[3]
109
110    def p_statement_expr(self, p):
111        'statement : expression'
112        print(p[1])
113
114    def p_expression_binop(self, p):
115        """
116        expression : expression PLUS expression
117                  | expression MINUS expression
118                  | expression TIMES expression
119                  | expression DIVIDE expression
120                  | expression EXP expression
121        """
122        #print [repr(p[i]) for i in range(0,4)]
123        if p[2] == '+'  : p[0] = p[1] + p[3]
124        elif p[2] == '-': p[0] = p[1] - p[3]
125        elif p[2] == '*': p[0] = p[1] * p[3]
126        elif p[2] == '/': p[0] = p[1] / p[3]
127        elif p[2] == '**': p[0] = p[1] ** p[3]
128
129    def p_expression_uminus(self, p):
130        'expression : MINUS expression %prec UMINUS'
131        p[0] = -p[2]
132
133    def p_expression_group(self, p):
134        'expression : LPAREN expression RPAREN'
135        p[0] = p[2]
136
137    def p_expression_number(self, p):
138        'expression : NUMBER'
139        p[0] = p[1]
140
141    def p_expression_name(self, p):
142        'expression : NAME'
143        try:
144            p[0] = self.names[p[1]]
145        except LookupError:
146            print("Undefined name '%s'" % p[1])
147            p[0] = 0
148
149    def p_error(self, p):
150        if p:
151            print("Syntax error at '%s'" % p.value)
152        else:
153            print("Syntax error at EOF")
154
155if __name__ == '__main__':
156    calc = Calc()
157    calc.run()
158