yacc_badprec.py revision 4479:61d3ed46e373 
1# -----------------------------------------------------------------------------
2# yacc_badprec.py
3#
4# Bad precedence specifier
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 = "blah"
16
17# dictionary of names
18names = { }
19
20def p_statement_assign(t):
21    'statement : NAME EQUALS expression'
22    names[t[1]] = t[3]
23
24def p_statement_expr(t):
25    'statement : expression'
26    print t[1]
27
28def 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[3] == '/': t[0] = t[1] / t[3]
37
38def p_expression_uminus(t):
39    'expression : MINUS expression %prec UMINUS'
40    t[0] = -t[2]
41
42def p_expression_group(t):
43    'expression : LPAREN expression RPAREN'
44    t[0] = t[2]
45
46def p_expression_number(t):
47    'expression : NUMBER'
48    t[0] = t[1]
49
50def 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
58def p_error(t):
59    print "Syntax error at '%s'" % t.value
60
61yacc.yacc()
62
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