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comparison ply-3.8/test/pkg_test2/parsing/calcparse.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_simple.py
3 #
4 # A simple, properly specifier grammar
5 # -----------------------------------------------------------------------------
6
7 from .calclex import tokens
8 from ply import yacc
9
10 # Parsing rules
11 precedence = (
12 ('left','PLUS','MINUS'),
13 ('left','TIMES','DIVIDE'),
14 ('right','UMINUS'),
15 )
16
17 # dictionary of names
18 names = { }
19
20 def p_statement_assign(t):
21 'statement : NAME EQUALS expression'
22 names[t[1]] = t[3]
23
24 def p_statement_expr(t):
25 'statement : expression'
26 t[0] = t[1]
27
28 def p_expression_binop(t):
29 '''expression : expression PLUS expression
30 | expression MINUS expression
31 | expression TIMES expression
32 | expression DIVIDE expression'''
33 if t[2] == '+' : t[0] = t[1] + t[3]
34 elif t[2] == '-': t[0] = t[1] - t[3]
35 elif t[2] == '*': t[0] = t[1] * t[3]
36 elif t[2] == '/': t[0] = t[1] / t[3]
37
38 def p_expression_uminus(t):
39 'expression : MINUS expression %prec UMINUS'
40 t[0] = -t[2]
41
42 def p_expression_group(t):
43 'expression : LPAREN expression RPAREN'
44 t[0] = t[2]
45
46 def p_expression_number(t):
47 'expression : NUMBER'
48 t[0] = t[1]
49
50 def p_expression_name(t):
51 'expression : NAME'
52 try:
53 t[0] = names[t[1]]
54 except LookupError:
55 print("Undefined name '%s'" % t[1])
56 t[0] = 0
57
58 def p_error(t):
59 print("Syntax error at '%s'" % t.value)
60
61 parser = yacc.yacc(tabmodule='calcparsetab')
62
63
64
65
66