ext/ply/test/yacc_badtok.py

   1 # -----------------------------------------------------------------------------
   2 # yacc_badtok.py
   3 #
   4 # A grammar, but tokens is a bad datatype
   5 # -----------------------------------------------------------------------------
   6
   7 import sys
   8 sys.tracebacklimit = 0
   9
  10 sys.path.insert(0,"..")
  11 import ply.yacc as yacc
  12
  13 tokens = "Hello"
  14
  15 # Parsing rules
  16 precedence = (
  17     ('left','PLUS','MINUS'),
  18     ('left','TIMES','DIVIDE'),
  19     ('right','UMINUS'),
  20     )
  21
  22 # dictionary of names
  23 names = { }
  24
  25 def p_statement_assign(t):
  26     'statement : NAME EQUALS expression'
  27     names[t[1]] = t[3]
  28
  29 def p_statement_expr(t):
  30     'statement : expression'
  31     print t[1]
  32
  33 def p_expression_binop(t):
  34     '''expression : expression PLUS expression
  35                   | expression MINUS expression
  36                   | expression TIMES expression
  37                   | expression DIVIDE expression'''
  38     if t[2] == '+'  : t[0] = t[1] + t[3]
  39     elif t[2] == '-': t[0] = t[1] - t[3]
  40     elif t[2] == '*': t[0] = t[1] * t[3]
  41     elif t[3] == '/': t[0] = t[1] / t[3]
  42
  43 def p_expression_uminus(t):
  44     'expression : MINUS expression %prec UMINUS'
  45     t[0] = -t[2]
  46
  47 def p_expression_group(t):
  48     'expression : LPAREN expression RPAREN'
  49     t[0] = t[2]
  50
  51 def p_expression_number(t):
  52     'expression : NUMBER'
  53     t[0] = t[1]
  54
  55 def p_expression_name(t):
  56     'expression : NAME'
  57     try:
  58         t[0] = names[t[1]]
  59     except LookupError:
  60         print "Undefined name '%s'" % t[1]
  61         t[0] = 0
  62
  63 def p_error(t):
  64     print "Syntax error at '%s'" % t.value
  65
  66 yacc.yacc()
  67
  68
  69
  70