|
7267
|
1 # -----------------------------------------------------------------------------
|
|
|
2 # calc.py
|
|
|
3 #
|
|
|
4 # A simple calculator with variables. This is from O'Reilly's
|
|
|
5 # "Lex and Yacc", p. 63.
|
|
|
6 #
|
|
|
7 # This example uses unicode strings for tokens, docstrings, and input.
|
|
|
8 # -----------------------------------------------------------------------------
|
|
|
9
|
|
|
10 import sys
|
|
|
11 sys.path.insert(0,"../..")
|
|
|
12
|
|
|
13 tokens = (
|
|
|
14 'NAME','NUMBER',
|
|
|
15 'PLUS','MINUS','TIMES','DIVIDE','EQUALS',
|
|
|
16 'LPAREN','RPAREN',
|
|
|
17 )
|
|
|
18
|
|
|
19 # Tokens
|
|
|
20
|
|
|
21 t_PLUS = ur'\+'
|
|
|
22 t_MINUS = ur'-'
|
|
|
23 t_TIMES = ur'\*'
|
|
|
24 t_DIVIDE = ur'/'
|
|
|
25 t_EQUALS = ur'='
|
|
|
26 t_LPAREN = ur'\('
|
|
|
27 t_RPAREN = ur'\)'
|
|
|
28 t_NAME = ur'[a-zA-Z_][a-zA-Z0-9_]*'
|
|
|
29
|
|
|
30 def t_NUMBER(t):
|
|
|
31 ur'\d+'
|
|
|
32 try:
|
|
|
33 t.value = int(t.value)
|
|
|
34 except ValueError:
|
|
|
35 print "Integer value too large", t.value
|
|
|
36 t.value = 0
|
|
|
37 return t
|
|
|
38
|
|
|
39 t_ignore = u" \t"
|
|
|
40
|
|
|
41 def t_newline(t):
|
|
|
42 ur'\n+'
|
|
|
43 t.lexer.lineno += t.value.count("\n")
|
|
|
44
|
|
|
45 def t_error(t):
|
|
|
46 print "Illegal character '%s'" % t.value[0]
|
|
|
47 t.lexer.skip(1)
|
|
|
48
|
|
|
49 # Build the lexer
|
|
|
50 import ply.lex as lex
|
|
|
51 lex.lex()
|
|
|
52
|
|
|
53 # Parsing rules
|
|
|
54
|
|
|
55 precedence = (
|
|
|
56 ('left','PLUS','MINUS'),
|
|
|
57 ('left','TIMES','DIVIDE'),
|
|
|
58 ('right','UMINUS'),
|
|
|
59 )
|
|
|
60
|
|
|
61 # dictionary of names
|
|
|
62 names = { }
|
|
|
63
|
|
|
64 def p_statement_assign(p):
|
|
|
65 'statement : NAME EQUALS expression'
|
|
|
66 names[p[1]] = p[3]
|
|
|
67
|
|
|
68 def p_statement_expr(p):
|
|
|
69 'statement : expression'
|
|
|
70 print p[1]
|
|
|
71
|
|
|
72 def p_expression_binop(p):
|
|
|
73 '''expression : expression PLUS expression
|
|
|
74 | expression MINUS expression
|
|
|
75 | expression TIMES expression
|
|
|
76 | expression DIVIDE expression'''
|
|
|
77 if p[2] == u'+' : p[0] = p[1] + p[3]
|
|
|
78 elif p[2] == u'-': p[0] = p[1] - p[3]
|
|
|
79 elif p[2] == u'*': p[0] = p[1] * p[3]
|
|
|
80 elif p[2] == u'/': p[0] = p[1] / p[3]
|
|
|
81
|
|
|
82 def p_expression_uminus(p):
|
|
|
83 'expression : MINUS expression %prec UMINUS'
|
|
|
84 p[0] = -p[2]
|
|
|
85
|
|
|
86 def p_expression_group(p):
|
|
|
87 'expression : LPAREN expression RPAREN'
|
|
|
88 p[0] = p[2]
|
|
|
89
|
|
|
90 def p_expression_number(p):
|
|
|
91 'expression : NUMBER'
|
|
|
92 p[0] = p[1]
|
|
|
93
|
|
|
94 def p_expression_name(p):
|
|
|
95 'expression : NAME'
|
|
|
96 try:
|
|
|
97 p[0] = names[p[1]]
|
|
|
98 except LookupError:
|
|
|
99 print "Undefined name '%s'" % p[1]
|
|
|
100 p[0] = 0
|
|
|
101
|
|
|
102 def p_error(p):
|
|
|
103 if p:
|
|
|
104 print "Syntax error at '%s'" % p.value
|
|
|
105 else:
|
|
|
106 print "Syntax error at EOF"
|
|
|
107
|
|
|
108 import ply.yacc as yacc
|
|
|
109 yacc.yacc()
|
|
|
110
|
|
|
111 while 1:
|
|
|
112 try:
|
|
|
113 s = raw_input('calc > ')
|
|
|
114 except EOFError:
|
|
|
115 break
|
|
|
116 if not s: continue
|
|
|
117 yacc.parse(unicode(s))
|
