1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
|
#!/usr/bin/env python
# -----------------------------------------------------------------------------
# calc.py
#
# A simple calculator with variables. This is from O'Reilly's
# "Lex and Yacc", p. 63.
#
# Class-based example contributed to PLY by David McNab
# -----------------------------------------------------------------------------
import sys
sys.path.insert(0, "../..")
import ply.lex as lex
import ply.yacc as yacc
import os
class Parser:
"""
Base class for a lexer/parser that has the rules defined as methods
"""
tokens = ()
precedence = ()
def __init__(self, **kw):
self.debug = kw.get('debug', 0)
self.names = {}
try:
modname = os.path.split(os.path.splitext(__file__)[0])[
1] + "_" + self.__class__.__name__
except:
modname = "parser" + "_" + self.__class__.__name__
self.debugfile = modname + ".dbg"
# print self.debugfile
# Build the lexer and parser
lex.lex(module=self, debug=self.debug)
yacc.yacc(module=self,
debug=self.debug,
debugfile=self.debugfile)
def run(self):
while True:
try:
s = input('calc > ')
except EOFError:
break
if not s:
continue
yacc.parse(s)
class Calc(Parser):
tokens = (
'NAME', 'NUMBER',
'PLUS', 'MINUS', 'EXP', 'TIMES', 'DIVIDE', 'EQUALS',
'LPAREN', 'RPAREN',
)
# Tokens
t_PLUS = r'\+'
t_MINUS = r'-'
t_EXP = r'\*\*'
t_TIMES = r'\*'
t_DIVIDE = r'/'
t_EQUALS = r'='
t_LPAREN = r'\('
t_RPAREN = r'\)'
t_NAME = r'[a-zA-Z_][a-zA-Z0-9_]*'
def t_NUMBER(self, t):
r'\d+'
try:
t.value = int(t.value)
except ValueError:
print("Integer value too large %s" % t.value)
t.value = 0
# print "parsed number %s" % repr(t.value)
return t
t_ignore = " \t"
def t_newline(self, t):
r'\n+'
t.lexer.lineno += t.value.count("\n")
def t_error(self, t):
print("Illegal character '%s'" % t.value[0])
t.lexer.skip(1)
# Parsing rules
precedence = (
('left', 'PLUS', 'MINUS'),
('left', 'TIMES', 'DIVIDE'),
('left', 'EXP'),
('right', 'UMINUS'),
)
def p_statement_assign(self, p):
'statement : NAME EQUALS expression'
self.names[p[1]] = p[3]
def p_statement_expr(self, p):
'statement : expression'
print(p[1])
def p_expression_binop(self, p):
"""
expression : expression PLUS expression
| expression MINUS expression
| expression TIMES expression
| expression DIVIDE expression
| expression EXP expression
"""
# print [repr(p[i]) for i in range(0,4)]
if p[2] == '+':
p[0] = p[1] + p[3]
elif p[2] == '-':
p[0] = p[1] - p[3]
elif p[2] == '*':
p[0] = p[1] * p[3]
elif p[2] == '/':
p[0] = p[1] / p[3]
elif p[2] == '**':
p[0] = p[1] ** p[3]
def p_expression_uminus(self, p):
'expression : MINUS expression %prec UMINUS'
p[0] = -p[2]
def p_expression_group(self, p):
'expression : LPAREN expression RPAREN'
p[0] = p[2]
def p_expression_number(self, p):
'expression : NUMBER'
p[0] = p[1]
def p_expression_name(self, p):
'expression : NAME'
try:
p[0] = self.names[p[1]]
except LookupError:
print("Undefined name '%s'" % p[1])
p[0] = 0
def p_error(self, p):
if p:
print("Syntax error at '%s'" % p.value)
else:
print("Syntax error at EOF")
if __name__ == '__main__':
calc = Calc()
calc.run()
|
