|
7267
|
1 # -----------------------------------------------------------------------------
|
|
|
2 # calc.py
|
|
|
3 #
|
|
|
4 # A calculator parser that makes use of closures. The function make_calculator()
|
|
|
5 # returns a function that accepts an input string and returns a result. All
|
|
|
6 # lexing rules, parsing rules, and internal state are held inside the function.
|
|
|
7 # -----------------------------------------------------------------------------
|
|
|
8
|
|
|
9 import sys
|
|
|
10 sys.path.insert(0,"../..")
|
|
|
11
|
|
|
12 if sys.version_info[0] >= 3:
|
|
|
13 raw_input = input
|
|
|
14
|
|
|
15 # Make a calculator function
|
|
|
16
|
|
|
17 def make_calculator():
|
|
|
18 import ply.lex as lex
|
|
|
19 import ply.yacc as yacc
|
|
|
20
|
|
|
21 # ------- Internal calculator state
|
|
|
22
|
|
|
23 variables = { } # Dictionary of stored variables
|
|
|
24
|
|
|
25 # ------- Calculator tokenizing rules
|
|
|
26
|
|
|
27 tokens = (
|
|
|
28 'NAME','NUMBER',
|
|
|
29 )
|
|
|
30
|
|
|
31 literals = ['=','+','-','*','/', '(',')']
|
|
|
32
|
|
|
33 t_ignore = " \t"
|
|
|
34
|
|
|
35 t_NAME = r'[a-zA-Z_][a-zA-Z0-9_]*'
|
|
|
36
|
|
|
37 def t_NUMBER(t):
|
|
|
38 r'\d+'
|
|
|
39 t.value = int(t.value)
|
|
|
40 return 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 lexer = lex.lex()
|
|
|
52
|
|
|
53 # ------- Calculator parsing rules
|
|
|
54
|
|
|
55 precedence = (
|
|
|
56 ('left','+','-'),
|
|
|
57 ('left','*','/'),
|
|
|
58 ('right','UMINUS'),
|
|
|
59 )
|
|
|
60
|
|
|
61 def p_statement_assign(p):
|
|
|
62 'statement : NAME "=" expression'
|
|
|
63 variables[p[1]] = p[3]
|
|
|
64 p[0] = None
|
|
|
65
|
|
|
66 def p_statement_expr(p):
|
|
|
67 'statement : expression'
|
|
|
68 p[0] = p[1]
|
|
|
69
|
|
|
70 def p_expression_binop(p):
|
|
|
71 '''expression : expression '+' expression
|
|
|
72 | expression '-' expression
|
|
|
73 | expression '*' expression
|
|
|
74 | expression '/' expression'''
|
|
|
75 if p[2] == '+' : p[0] = p[1] + p[3]
|
|
|
76 elif p[2] == '-': p[0] = p[1] - p[3]
|
|
|
77 elif p[2] == '*': p[0] = p[1] * p[3]
|
|
|
78 elif p[2] == '/': p[0] = p[1] / p[3]
|
|
|
79
|
|
|
80 def p_expression_uminus(p):
|
|
|
81 "expression : '-' expression %prec UMINUS"
|
|
|
82 p[0] = -p[2]
|
|
|
83
|
|
|
84 def p_expression_group(p):
|
|
|
85 "expression : '(' expression ')'"
|
|
|
86 p[0] = p[2]
|
|
|
87
|
|
|
88 def p_expression_number(p):
|
|
|
89 "expression : NUMBER"
|
|
|
90 p[0] = p[1]
|
|
|
91
|
|
|
92 def p_expression_name(p):
|
|
|
93 "expression : NAME"
|
|
|
94 try:
|
|
|
95 p[0] = variables[p[1]]
|
|
|
96 except LookupError:
|
|
|
97 print("Undefined name '%s'" % p[1])
|
|
|
98 p[0] = 0
|
|
|
99
|
|
|
100 def p_error(p):
|
|
|
101 if p:
|
|
|
102 print("Syntax error at '%s'" % p.value)
|
|
|
103 else:
|
|
|
104 print("Syntax error at EOF")
|
|
|
105
|
|
|
106
|
|
|
107 # Build the parser
|
|
|
108 parser = yacc.yacc()
|
|
|
109
|
|
|
110 # ------- Input function
|
|
|
111
|
|
|
112 def input(text):
|
|
|
113 result = parser.parse(text,lexer=lexer)
|
|
|
114 return result
|
|
|
115
|
|
|
116 return input
|
|
|
117
|
|
|
118 # Make a calculator object and use it
|
|
|
119 calc = make_calculator()
|
|
|
120
|
|
|
121 while True:
|
|
|
122 try:
|
|
|
123 s = raw_input("calc > ")
|
|
|
124 except EOFError:
|
|
|
125 break
|
|
|
126 r = calc(s)
|
|
|
127 if r:
|
|
|
128 print(r)
|
|
|
129
|
|
|
130
|
