ext/ply/test/yacc_notok.py

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