yacc_rr.py revision 4479 
1# -----------------------------------------------------------------------------
2# yacc_rr.py
3#
4# A grammar with a reduce/reduce conflict
5# -----------------------------------------------------------------------------
6import sys
7sys.tracebacklimit = 0
8
9sys.path.insert(0,"..")
10import ply.yacc as yacc
11
12from calclex import tokens
13
14# Parsing rules
15precedence = (
16    ('left','PLUS','MINUS'),
17    ('left','TIMES','DIVIDE'),
18    ('right','UMINUS'),
19    )
20
21# dictionary of names
22names = { }
23
24def p_statement_assign(t):
25    'statement : NAME EQUALS expression'
26    names[t[1]] = t[3]
27
28def p_statement_assign_2(t):
29    'statement : NAME EQUALS NUMBER'
30    names[t[1]] = t[3]
31
32def p_statement_expr(t):
33    'statement : expression'
34    print t[1]
35
36def p_expression_binop(t):
37    '''expression : expression PLUS expression
38                  | expression MINUS expression
39                  | expression TIMES expression
40                  | expression DIVIDE expression'''
41    if t[2] == '+'  : t[0] = t[1] + t[3]
42    elif t[2] == '-': t[0] = t[1] - t[3]
43    elif t[2] == '*': t[0] = t[1] * t[3]
44    elif t[3] == '/': t[0] = t[1] / t[3]
45
46def p_expression_uminus(t):
47    'expression : MINUS expression %prec UMINUS'
48    t[0] = -t[2]
49
50def p_expression_group(t):
51    'expression : LPAREN expression RPAREN'
52    t[0] = t[2]
53
54def p_expression_number(t):
55    'expression : NUMBER'
56    t[0] = t[1]
57
58def p_expression_name(t):
59    'expression : NAME'
60    try:
61        t[0] = names[t[1]]
62    except LookupError:
63        print "Undefined name '%s'" % t[1]
64        t[0] = 0
65
66def p_error(t):
67    print "Syntax error at '%s'" % t.value
68
69yacc.yacc()
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