1# -----------------------------------------------------------------------------
2# calc.py
3#
4# A simple calculator with variables.  Asks the user for more input and
5# demonstrates the use of the t_eof() rule.
6# -----------------------------------------------------------------------------
7
8import sys
9sys.path.insert(0, "../..")
10
11if sys.version_info[0] >= 3:
12    raw_input = input
13
14tokens = (
15    'NAME', 'NUMBER',
16)
17
18literals = ['=', '+', '-', '*', '/', '(', ')']
19
20# Tokens
21
22t_NAME = r'[a-zA-Z_][a-zA-Z0-9_]*'
23
24
25def t_NUMBER(t):
26    r'\d+'
27    t.value = int(t.value)
28    return t
29
30t_ignore = " \t"
31
32
33def t_newline(t):
34    r'\n+'
35    t.lexer.lineno += t.value.count("\n")
36
37
38def t_eof(t):
39    more = raw_input('... ')
40    if more:
41        t.lexer.input(more + '\n')
42        return t.lexer.token()
43    else:
44        return None
45
46
47def t_error(t):
48    print("Illegal character '%s'" % t.value[0])
49    t.lexer.skip(1)
50
51# Build the lexer
52import ply.lex as lex
53lex.lex()
54
55# Parsing rules
56
57precedence = (
58    ('left', '+', '-'),
59    ('left', '*', '/'),
60    ('right', 'UMINUS'),
61)
62
63# dictionary of names
64names = {}
65
66
67def p_statement_assign(p):
68    'statement : NAME "=" expression'
69    names[p[1]] = p[3]
70
71
72def p_statement_expr(p):
73    'statement : expression'
74    print(p[1])
75
76
77def p_expression_binop(p):
78    '''expression : expression '+' expression
79                  | expression '-' expression
80                  | expression '*' expression
81                  | expression '/' expression'''
82    if p[2] == '+':
83        p[0] = p[1] + p[3]
84    elif p[2] == '-':
85        p[0] = p[1] - p[3]
86    elif p[2] == '*':
87        p[0] = p[1] * p[3]
88    elif p[2] == '/':
89        p[0] = p[1] / p[3]
90
91
92def p_expression_uminus(p):
93    "expression : '-' expression %prec UMINUS"
94    p[0] = -p[2]
95
96
97def p_expression_group(p):
98    "expression : '(' expression ')'"
99    p[0] = p[2]
100
101
102def p_expression_number(p):
103    "expression : NUMBER"
104    p[0] = p[1]
105
106
107def p_expression_name(p):
108    "expression : NAME"
109    try:
110        p[0] = names[p[1]]
111    except LookupError:
112        print("Undefined name '%s'" % p[1])
113        p[0] = 0
114
115
116def p_error(p):
117    if p:
118        print("Syntax error at '%s'" % p.value)
119    else:
120        print("Syntax error at EOF")
121
122import ply.yacc as yacc
123yacc.yacc()
124
125while 1:
126    try:
127        s = raw_input('calc > ')
128    except EOFError:
129        break
130    if not s:
131        continue
132    yacc.parse(s + '\n')
133