ext/ply/example/optcalc/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     'PLUS','MINUS','TIMES','DIVIDE','EQUALS',
  14     'LPAREN','RPAREN',
  15     )
  16
  17 # Tokens
  18
  19 t_PLUS    = r'\+'
  20 t_MINUS   = r'-'
  21 t_TIMES   = r'\*'
  22 t_DIVIDE  = r'/'
  23 t_EQUALS  = r'='
  24 t_LPAREN  = r'\('
  25 t_RPAREN  = r'\)'
  26 t_NAME    = r'[a-zA-Z_][a-zA-Z0-9_]*'
  27
  28 def t_NUMBER(t):
  29     r'\d+'
  30     try:
  31         t.value = int(t.value)
  32     except ValueError:
  33         print "Integer value too large", t.value
  34         t.value = 0
  35     return t
  36
  37 t_ignore = " \t"
  38
  39 def t_newline(t):
  40     r'\n+'
  41     t.lexer.lineno += t.value.count("\n")
  42
  43 def t_error(t):
  44     print "Illegal character '%s'" % t.value[0]
  45     t.lexer.skip(1)
  46
  47 # Build the lexer
  48 import ply.lex as lex
  49 lex.lex(optimize=1)
  50
  51 # Parsing rules
  52
  53 precedence = (
  54     ('left','PLUS','MINUS'),
  55     ('left','TIMES','DIVIDE'),
  56     ('right','UMINUS'),
  57     )
  58
  59 # dictionary of names
  60 names = { }
  61
  62 def p_statement_assign(t):
  63     'statement : NAME EQUALS expression'
  64     names[t[1]] = t[3]
  65
  66 def p_statement_expr(t):
  67     'statement : expression'
  68     print t[1]
  69
  70 def p_expression_binop(t):
  71     '''expression : expression PLUS expression
  72                   | expression MINUS expression
  73                   | expression TIMES expression
  74                   | expression DIVIDE expression'''
  75     if t[2] == '+'  : t[0] = t[1] + t[3]
  76     elif t[2] == '-': t[0] = t[1] - t[3]
  77     elif t[2] == '*': t[0] = t[1] * t[3]
  78     elif t[2] == '/': t[0] = t[1] / t[3]
  79     elif t[2] == '<': t[0] = t[1] < t[3]
  80
  81 def p_expression_uminus(t):
  82     'expression : MINUS expression %prec UMINUS'
  83     t[0] = -t[2]
  84
  85 def p_expression_group(t):
  86     'expression : LPAREN expression RPAREN'
  87     t[0] = t[2]
  88
  89 def p_expression_number(t):
  90     'expression : NUMBER'
  91     t[0] = t[1]
  92
  93 def p_expression_name(t):
  94     'expression : NAME'
  95     try:
  96         t[0] = names[t[1]]
  97     except LookupError:
  98         print "Undefined name '%s'" % t[1]
  99         t[0] = 0
 100
 101 def p_error(t):
 102     print "Syntax error at '%s'" % t.value
 103
 104 import ply.yacc as yacc
 105 yacc.yacc(optimize=1)
 106
 107 while 1:
 108     try:
 109         s = raw_input('calc > ')
 110     except EOFError:
 111         break
 112     yacc.parse(s)
 113