--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/ply-3.8/example/unicalc/calc.py	Wed Mar 23 02:40:16 2016 +0000
@@ -0,0 +1,117 @@
+# -----------------------------------------------------------------------------
+# calc.py
+#
+# A simple calculator with variables.   This is from O'Reilly's
+# "Lex and Yacc", p. 63.
+#
+# This example uses unicode strings for tokens, docstrings, and input.
+# -----------------------------------------------------------------------------
+
+import sys
+sys.path.insert(0,"../..")
+
+tokens = (
+    'NAME','NUMBER',
+    'PLUS','MINUS','TIMES','DIVIDE','EQUALS',
+    'LPAREN','RPAREN',
+    )
+
+# Tokens
+
+t_PLUS    = ur'\+'
+t_MINUS   = ur'-'
+t_TIMES   = ur'\*'
+t_DIVIDE  = ur'/'
+t_EQUALS  = ur'='
+t_LPAREN  = ur'\('
+t_RPAREN  = ur'\)'
+t_NAME    = ur'[a-zA-Z_][a-zA-Z0-9_]*'
+
+def t_NUMBER(t):
+    ur'\d+'
+    try:
+        t.value = int(t.value)
+    except ValueError:
+        print "Integer value too large", t.value
+        t.value = 0
+    return t
+
+t_ignore = u" \t"
+
+def t_newline(t):
+    ur'\n+'
+    t.lexer.lineno += t.value.count("\n")
+    
+def t_error(t):
+    print "Illegal character '%s'" % t.value[0]
+    t.lexer.skip(1)
+    
+# Build the lexer
+import ply.lex as lex
+lex.lex()
+
+# Parsing rules
+
+precedence = (
+    ('left','PLUS','MINUS'),
+    ('left','TIMES','DIVIDE'),
+    ('right','UMINUS'),
+    )
+
+# dictionary of names
+names = { }
+
+def p_statement_assign(p):
+    'statement : NAME EQUALS expression'
+    names[p[1]] = p[3]
+
+def p_statement_expr(p):
+    'statement : expression'
+    print p[1]
+
+def p_expression_binop(p):
+    '''expression : expression PLUS expression
+                  | expression MINUS expression
+                  | expression TIMES expression
+                  | expression DIVIDE expression'''
+    if p[2] == u'+'  : p[0] = p[1] + p[3]
+    elif p[2] == u'-': p[0] = p[1] - p[3]
+    elif p[2] == u'*': p[0] = p[1] * p[3]
+    elif p[2] == u'/': p[0] = p[1] / p[3]
+
+def p_expression_uminus(p):
+    'expression : MINUS expression %prec UMINUS'
+    p[0] = -p[2]
+
+def p_expression_group(p):
+    'expression : LPAREN expression RPAREN'
+    p[0] = p[2]
+
+def p_expression_number(p):
+    'expression : NUMBER'
+    p[0] = p[1]
+
+def p_expression_name(p):
+    'expression : NAME'
+    try:
+        p[0] = names[p[1]]
+    except LookupError:
+        print "Undefined name '%s'" % p[1]
+        p[0] = 0
+
+def p_error(p):
+    if p:
+        print "Syntax error at '%s'" % p.value
+    else:
+        print "Syntax error at EOF"
+
+import ply.yacc as yacc
+yacc.yacc()
+
+while 1:
+    try:
+        s = raw_input('calc > ')
+    except EOFError:
+        break
+    if not s: continue
+    yacc.parse(unicode(s))