1# -----------------------------------------------------------------------------
2# yacc_nodoc.py
3#
4# Rule with a missing doc-string
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_expr(t):
28    print(t[1])
29
30def p_expression_binop(t):
31    '''expression : expression PLUS expression
32                  | expression MINUS expression
33                  | expression TIMES expression
34                  | expression DIVIDE expression'''
35    if t[2] == '+'  : t[0] = t[1] + t[3]
36    elif t[2] == '-': t[0] = t[1] - t[3]
37    elif t[2] == '*': t[0] = t[1] * t[3]
38    elif t[2] == '/': t[0] = t[1] / t[3]
39
40def p_expression_uminus(t):
41    'expression : MINUS expression %prec UMINUS'
42    t[0] = -t[2]
43
44def p_expression_group(t):
45    'expression : LPAREN expression RPAREN'
46    t[0] = t[2]
47
48def p_expression_number(t):
49    'expression : NUMBER'
50    t[0] = t[1]
51
52def p_expression_name(t):
53    'expression : NAME'
54    try:
55        t[0] = names[t[1]]
56    except LookupError:
57        print("Undefined name '%s'" % t[1])
58        t[0] = 0
59
60def p_error(t):
61    print("Syntax error at '%s'" % t.value)
62
63yacc.yacc()
64
65
66
67
68