ext/ply/test/yacc_uprec.py

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