1# -----------------------------------------------------------------------------
2# yacc_rr.py
3#
4# A grammar with a reduce/reduce conflict
5# -----------------------------------------------------------------------------
6import sys
7
8if ".." not in sys.path: sys.path.insert(0,"..")
9import ply.yacc as yacc
10
11from calclex import tokens
12
13# Parsing rules
14precedence = (
15    ('left','PLUS','MINUS'),
16    ('left','TIMES','DIVIDE'),
17    ('right','UMINUS'),
18    )
19
20# dictionary of names
21names = { }
22
23def p_statement_assign(t):
24    'statement : NAME EQUALS expression'
25    names[t[1]] = t[3]
26
27def p_statement_assign_2(t):
28    'statement : NAME EQUALS NUMBER'
29    names[t[1]] = t[3]
30
31def p_statement_expr(t):
32    'statement : expression'
33    print(t[1])
34
35def p_expression_binop(t):
36    '''expression : expression PLUS expression
37                  | expression MINUS expression
38                  | expression TIMES expression
39                  | expression DIVIDE expression'''
40    if t[2] == '+'  : t[0] = t[1] + t[3]
41    elif 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
45def p_expression_uminus(t):
46    'expression : MINUS expression %prec UMINUS'
47    t[0] = -t[2]
48
49def p_expression_group(t):
50    'expression : LPAREN expression RPAREN'
51    t[0] = t[2]
52
53def p_expression_number(t):
54    'expression : NUMBER'
55    t[0] = t[1]
56
57def p_expression_name(t):
58    'expression : NAME'
59    try:
60        t[0] = names[t[1]]
61    except LookupError:
62        print("Undefined name '%s'" % t[1])
63        t[0] = 0
64
65def p_error(t):
66    print("Syntax error at '%s'" % t.value)
67
68yacc.yacc()
69
70
71
72
73