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comparison ply-3.8/example/optcalc/calc.py @ 7267:343ff337a19b

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<ais523> ` tar -xf ply-3.8.tar.gz
author HackBot
date Wed, 23 Mar 2016 02:40:16 +0000
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7266:61a39a120dee 7267:343ff337a19b
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
8 import sys
9 sys.path.insert(0,"../..")
10
11 if sys.version_info[0] >= 3:
12 raw_input = input
13
14 tokens = (
15 'NAME','NUMBER',
16 'PLUS','MINUS','TIMES','DIVIDE','EQUALS',
17 'LPAREN','RPAREN',
18 )
19
20 # Tokens
21
22 t_PLUS = r'\+'
23 t_MINUS = r'-'
24 t_TIMES = r'\*'
25 t_DIVIDE = r'/'
26 t_EQUALS = r'='
27 t_LPAREN = r'\('
28 t_RPAREN = r'\)'
29 t_NAME = r'[a-zA-Z_][a-zA-Z0-9_]*'
30
31 def t_NUMBER(t):
32 r'\d+'
33 try:
34 t.value = int(t.value)
35 except ValueError:
36 print("Integer value too large %s" % t.value)
37 t.value = 0
38 return t
39
40 t_ignore = " \t"
41
42 def t_newline(t):
43 r'\n+'
44 t.lexer.lineno += t.value.count("\n")
45
46 def t_error(t):
47 print("Illegal character '%s'" % t.value[0])
48 t.lexer.skip(1)
49
50 # Build the lexer
51 import ply.lex as lex
52 lex.lex(optimize=1)
53
54 # Parsing rules
55
56 precedence = (
57 ('left','PLUS','MINUS'),
58 ('left','TIMES','DIVIDE'),
59 ('right','UMINUS'),
60 )
61
62 # dictionary of names
63 names = { }
64
65 def p_statement_assign(t):
66 'statement : NAME EQUALS expression'
67 names[t[1]] = t[3]
68
69 def p_statement_expr(t):
70 'statement : expression'
71 print(t[1])
72
73 def p_expression_binop(t):
74 '''expression : expression PLUS expression
75 | expression MINUS expression
76 | expression TIMES expression
77 | expression DIVIDE expression'''
78 if t[2] == '+' : t[0] = t[1] + t[3]
79 elif t[2] == '-': t[0] = t[1] - t[3]
80 elif t[2] == '*': t[0] = t[1] * t[3]
81 elif t[2] == '/': t[0] = t[1] / t[3]
82 elif t[2] == '<': t[0] = t[1] < t[3]
83
84 def p_expression_uminus(t):
85 'expression : MINUS expression %prec UMINUS'
86 t[0] = -t[2]
87
88 def p_expression_group(t):
89 'expression : LPAREN expression RPAREN'
90 t[0] = t[2]
91
92 def p_expression_number(t):
93 'expression : NUMBER'
94 t[0] = t[1]
95
96 def p_expression_name(t):
97 'expression : NAME'
98 try:
99 t[0] = names[t[1]]
100 except LookupError:
101 print("Undefined name '%s'" % t[1])
102 t[0] = 0
103
104 def p_error(t):
105 if t:
106 print("Syntax error at '%s'" % t.value)
107 else:
108 print("Syntax error at EOF")
109
110 import ply.yacc as yacc
111 yacc.yacc(optimize=1)
112
113 while 1:
114 try:
115 s = raw_input('calc > ')
116 except EOFError:
117 break
118 yacc.parse(s)
119