ext/ply/example/calc/calc.py

   1 # -----------------------------------------------------------------------------
   2 # calc.py
   3 #
   4 # A simple calculator with variables.   This is from O'Reilly's
   5 # "Lex and Yacc", p. 63.
   6 # -----------------------------------------------------------------------------
   7
   8 import sys
   9 sys.path.insert(0,"../..")
  10
  11 tokens = (
  12     'NAME','NUMBER',
  13     )
  14
  15 literals = ['=','+','-','*','/', '(',')']
  16
  17 # Tokens
  18
  19 t_NAME    = r'[a-zA-Z_][a-zA-Z0-9_]*'
  20
  21 def t_NUMBER(t):
  22     r'\d+'
  23     try:
  24         t.value = int(t.value)
  25     except ValueError:
  26         print "Integer value too large", t.value
  27         t.value = 0
  28     return t
  29
  30 t_ignore = " \t"
  31
  32 def t_newline(t):
  33     r'\n+'
  34     t.lexer.lineno += t.value.count("\n")
  35
  36 def t_error(t):
  37     print "Illegal character '%s'" % t.value[0]
  38     t.lexer.skip(1)
  39
  40 # Build the lexer
  41 import ply.lex as lex
  42 lex.lex()
  43
  44 # Parsing rules
  45
  46 precedence = (
  47     ('left','+','-'),
  48     ('left','*','/'),
  49     ('right','UMINUS'),
  50     )
  51
  52 # dictionary of names
  53 names = { }
  54
  55 def p_statement_assign(p):
  56     'statement : NAME "=" expression'
  57     names[p[1]] = p[3]
  58
  59 def p_statement_expr(p):
  60     'statement : expression'
  61     print p[1]
  62
  63 def p_expression_binop(p):
  64     '''expression : expression '+' expression
  65                   | expression '-' expression
  66                   | expression '*' expression
  67                   | expression '/' expression'''
  68     if p[2] == '+'  : p[0] = p[1] + p[3]
  69     elif p[2] == '-': p[0] = p[1] - p[3]
  70     elif p[2] == '*': p[0] = p[1] * p[3]
  71     elif p[2] == '/': p[0] = p[1] / p[3]
  72
  73 def p_expression_uminus(p):
  74     "expression : '-' expression %prec UMINUS"
  75     p[0] = -p[2]
  76
  77 def p_expression_group(p):
  78     "expression : '(' expression ')'"
  79     p[0] = p[2]
  80
  81 def p_expression_number(p):
  82     "expression : NUMBER"
  83     p[0] = p[1]
  84
  85 def p_expression_name(p):
  86     "expression : NAME"
  87     try:
  88         p[0] = names[p[1]]
  89     except LookupError:
  90         print "Undefined name '%s'" % p[1]
  91         p[0] = 0
  92
  93 def p_error(p):
  94     print "Syntax error at '%s'" % p.value
  95
  96 import ply.yacc as yacc
  97 yacc.yacc()
  98
  99 while 1:
 100     try:
 101         s = raw_input('calc > ')
 102     except EOFError:
 103         break
 104     if not s: continue
 105     yacc.parse(s)