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comparison ply-3.8/test/yacc_sr.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 # yacc_sr.py
3 #
4 # A grammar with shift-reduce conflicts
5 # -----------------------------------------------------------------------------
6 import sys
7
8 if ".." not in sys.path: sys.path.insert(0,"..")
9 import ply.yacc as yacc
10
11 from calclex import tokens
12
13 # Parsing rules
14
15 # dictionary of names
16 names = { }
17
18 def p_statement_assign(t):
19 'statement : NAME EQUALS expression'
20 names[t[1]] = t[3]
21
22 def p_statement_expr(t):
23 'statement : expression'
24 print(t[1])
25
26 def p_expression_binop(t):
27 '''expression : expression PLUS expression
28 | expression MINUS expression
29 | expression TIMES expression
30 | expression DIVIDE expression'''
31 if t[2] == '+' : t[0] = t[1] + t[3]
32 elif t[2] == '-': t[0] = t[1] - t[3]
33 elif t[2] == '*': t[0] = t[1] * t[3]
34 elif t[2] == '/': t[0] = t[1] / t[3]
35
36 def p_expression_uminus(t):
37 'expression : MINUS expression'
38 t[0] = -t[2]
39
40 def p_expression_group(t):
41 'expression : LPAREN expression RPAREN'
42 t[0] = t[2]
43
44 def p_expression_number(t):
45 'expression : NUMBER'
46 t[0] = t[1]
47
48 def p_expression_name(t):
49 'expression : NAME'
50 try:
51 t[0] = names[t[1]]
52 except LookupError:
53 print("Undefined name '%s'" % t[1])
54 t[0] = 0
55
56 def p_error(t):
57 print("Syntax error at '%s'" % t.value)
58
59 yacc.yacc()
60
61
62
63