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1 # -----------------------------------------------------------------------------
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2 # calc.py
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3 #
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4 # A simple calculator with variables. This is from O'Reilly's
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5 # "Lex and Yacc", p. 63.
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6 # -----------------------------------------------------------------------------
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7
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8 import sys
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9 sys.path.insert(0,"../..")
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10
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11 if sys.version_info[0] >= 3:
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12 raw_input = input
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13
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14 tokens = (
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15 'NAME','NUMBER',
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16 'PLUS','MINUS','TIMES','DIVIDE','EQUALS',
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17 'LPAREN','RPAREN',
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18 )
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19
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20 # Tokens
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21
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22 t_PLUS = r'\+'
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23 t_MINUS = r'-'
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24 t_TIMES = r'\*'
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25 t_DIVIDE = r'/'
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26 t_EQUALS = r'='
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27 t_LPAREN = r'\('
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28 t_RPAREN = r'\)'
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29 t_NAME = r'[a-zA-Z_][a-zA-Z0-9_]*'
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30
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31 def t_NUMBER(t):
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32 r'\d+'
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33 try:
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34 t.value = int(t.value)
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35 except ValueError:
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36 print("Integer value too large %s" % t.value)
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37 t.value = 0
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38 return t
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39
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40 t_ignore = " \t"
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41
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42 def t_newline(t):
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43 r'\n+'
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44 t.lexer.lineno += t.value.count("\n")
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45
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46 def t_error(t):
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47 print("Illegal character '%s'" % t.value[0])
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48 t.lexer.skip(1)
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49
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50 # Build the lexer
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51 import ply.lex as lex
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52 lex.lex(optimize=1)
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53
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54 # Parsing rules
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55
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56 precedence = (
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57 ('left','PLUS','MINUS'),
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58 ('left','TIMES','DIVIDE'),
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59 ('right','UMINUS'),
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60 )
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61
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62 # dictionary of names
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63 names = { }
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64
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65 def p_statement_assign(t):
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66 'statement : NAME EQUALS expression'
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67 names[t[1]] = t[3]
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68
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69 def p_statement_expr(t):
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70 'statement : expression'
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71 print(t[1])
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72
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73 def p_expression_binop(t):
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74 '''expression : expression PLUS expression
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75 | expression MINUS expression
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76 | expression TIMES expression
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77 | expression DIVIDE expression'''
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78 if t[2] == '+' : t[0] = t[1] + t[3]
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79 elif t[2] == '-': t[0] = t[1] - t[3]
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80 elif t[2] == '*': t[0] = t[1] * t[3]
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81 elif t[2] == '/': t[0] = t[1] / t[3]
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82 elif t[2] == '<': t[0] = t[1] < t[3]
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83
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84 def p_expression_uminus(t):
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85 'expression : MINUS expression %prec UMINUS'
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86 t[0] = -t[2]
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87
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88 def p_expression_group(t):
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89 'expression : LPAREN expression RPAREN'
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90 t[0] = t[2]
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91
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92 def p_expression_number(t):
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93 'expression : NUMBER'
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94 t[0] = t[1]
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95
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96 def p_expression_name(t):
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97 'expression : NAME'
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98 try:
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99 t[0] = names[t[1]]
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100 except LookupError:
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101 print("Undefined name '%s'" % t[1])
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102 t[0] = 0
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103
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104 def p_error(t):
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105 if t:
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106 print("Syntax error at '%s'" % t.value)
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107 else:
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108 print("Syntax error at EOF")
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109
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110 import ply.yacc as yacc
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111 yacc.yacc(optimize=1)
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112
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113 while 1:
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114 try:
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115 s = raw_input('calc > ')
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116 except EOFError:
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117 break
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118 yacc.parse(s)
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119
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