yacc_badprec.py revision 2632:1bb2f91485ea 
1# -----------------------------------------------------------------------------
2# yacc_badprec.py
3#
4# Bad precedence specifier
5# -----------------------------------------------------------------------------
6import sys
7sys.tracebacklimit = 0
8
9from calclex import tokens
10
11# Parsing rules
12precedence = "blah"
13
14# dictionary of names
15names = { }
16
17def p_statement_assign(t):
18    'statement : NAME EQUALS expression'
19    names[t[1]] = t[3]
20
21def p_statement_expr(t):
22    'statement : expression'
23    print t[1]
24
25def p_expression_binop(t):
26    '''expression : expression PLUS expression
27                  | expression MINUS expression
28                  | expression TIMES expression
29                  | expression DIVIDE expression'''
30    if t[2] == '+'  : t[0] = t[1] + t[3]
31    elif t[2] == '-': t[0] = t[1] - t[3]
32    elif t[2] == '*': t[0] = t[1] * t[3]
33    elif t[3] == '/': t[0] = t[1] / t[3]
34
35def p_expression_uminus(t):
36    'expression : MINUS expression %prec UMINUS'
37    t[0] = -t[2]
38
39def p_expression_group(t):
40    'expression : LPAREN expression RPAREN'
41    t[0] = t[2]
42
43def p_expression_number(t):
44    'expression : NUMBER'
45    t[0] = t[1]
46
47def p_expression_name(t):
48    'expression : NAME'
49    try:
50        t[0] = names[t[1]]
51    except LookupError:
52        print "Undefined name '%s'" % t[1]
53        t[0] = 0
54
55def p_error(t):
56    print "Syntax error at '%s'" % t.value
57
58import yacc
59yacc.yacc()
60
61
62
63
64