yacc_rr.py revision 2632 
1# -----------------------------------------------------------------------------
2# yacc_rr.py
3#
4# A grammar with a reduce/reduce conflict
5# -----------------------------------------------------------------------------
6import sys
7sys.tracebacklimit = 0
8
9from calclex import tokens
10
11# Parsing rules
12precedence = (
13    ('left','PLUS','MINUS'),
14    ('left','TIMES','DIVIDE'),
15    ('right','UMINUS'),
16    )
17
18# dictionary of names
19names = { }
20
21def p_statement_assign(t):
22    'statement : NAME EQUALS expression'
23    names[t[1]] = t[3]
24
25def p_statement_assign_2(t):
26    'statement : NAME EQUALS NUMBER'
27    names[t[1]] = t[3]
28
29def p_statement_expr(t):
30    'statement : expression'
31    print t[1]
32
33def p_expression_binop(t):
34    '''expression : expression PLUS expression
35                  | expression MINUS expression
36                  | expression TIMES expression
37                  | expression DIVIDE expression'''
38    if t[2] == '+'  : t[0] = t[1] + t[3]
39    elif t[2] == '-': t[0] = t[1] - t[3]
40    elif t[2] == '*': t[0] = t[1] * t[3]
41    elif t[3] == '/': t[0] = t[1] / t[3]
42
43def p_expression_uminus(t):
44    'expression : MINUS expression %prec UMINUS'
45    t[0] = -t[2]
46
47def p_expression_group(t):
48    'expression : LPAREN expression RPAREN'
49    t[0] = t[2]
50
51def p_expression_number(t):
52    'expression : NUMBER'
53    t[0] = t[1]
54
55def p_expression_name(t):
56    'expression : NAME'
57    try:
58        t[0] = names[t[1]]
59    except LookupError:
60        print "Undefined name '%s'" % t[1]
61        t[0] = 0
62
63def p_error(t):
64    print "Syntax error at '%s'" % t.value
65
66import yacc
67yacc.yacc()
68
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72