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
|
|
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
|