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-rw-r--r--ext/ply/example/calc/calc.py108
1 files changed, 108 insertions, 0 deletions
diff --git a/ext/ply/example/calc/calc.py b/ext/ply/example/calc/calc.py
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+# -----------------------------------------------------------------------------
+# calc.py
+#
+# A simple calculator with variables. This is from O'Reilly's
+# "Lex and Yacc", p. 63.
+# -----------------------------------------------------------------------------
+
+tokens = (
+ 'NAME','NUMBER',
+ 'PLUS','MINUS','TIMES','DIVIDE','EQUALS',
+ 'LPAREN','RPAREN',
+ )
+
+# Tokens
+
+t_PLUS = r'\+'
+t_MINUS = r'-'
+t_TIMES = r'\*'
+t_DIVIDE = r'/'
+t_EQUALS = r'='
+t_LPAREN = r'\('
+t_RPAREN = r'\)'
+t_NAME = r'[a-zA-Z_][a-zA-Z0-9_]*'
+
+def t_NUMBER(t):
+ r'\d+'
+ try:
+ t.value = int(t.value)
+ except ValueError:
+ print "Integer value too large", t.value
+ t.value = 0
+ return t
+
+t_ignore = " \t"
+
+def t_newline(t):
+ r'\n+'
+ t.lineno += t.value.count("\n")
+
+def t_error(t):
+ print "Illegal character '%s'" % t.value[0]
+ t.skip(1)
+
+# Build the lexer
+import lex
+lex.lex()
+
+# Parsing rules
+
+precedence = (
+ ('left','PLUS','MINUS'),
+ ('left','TIMES','DIVIDE'),
+ ('right','UMINUS'),
+ )
+
+# dictionary of names
+names = { }
+
+def p_statement_assign(t):
+ 'statement : NAME EQUALS expression'
+ names[t[1]] = t[3]
+
+def p_statement_expr(t):
+ 'statement : expression'
+ print t[1]
+
+def p_expression_binop(t):
+ '''expression : expression PLUS expression
+ | expression MINUS expression
+ | expression TIMES expression
+ | expression DIVIDE expression'''
+ if t[2] == '+' : t[0] = t[1] + t[3]
+ elif t[2] == '-': t[0] = t[1] - t[3]
+ elif t[2] == '*': t[0] = t[1] * t[3]
+ elif t[2] == '/': t[0] = t[1] / t[3]
+
+def p_expression_uminus(t):
+ 'expression : MINUS expression %prec UMINUS'
+ t[0] = -t[2]
+
+def p_expression_group(t):
+ 'expression : LPAREN expression RPAREN'
+ t[0] = t[2]
+
+def p_expression_number(t):
+ 'expression : NUMBER'
+ t[0] = t[1]
+
+def p_expression_name(t):
+ 'expression : NAME'
+ try:
+ t[0] = names[t[1]]
+ except LookupError:
+ print "Undefined name '%s'" % t[1]
+ t[0] = 0
+
+def p_error(t):
+ print "Syntax error at '%s'" % t.value
+
+import yacc
+yacc.yacc()
+
+while 1:
+ try:
+ s = raw_input('calc > ')
+ except EOFError:
+ break
+ yacc.parse(s)