1 files changed, 165 insertions, 0 deletions
diff --git a/third_party/python/ply/example/classcalc/calc.py b/third_party/python/ply/example/classcalc/calc.py
new file mode 100755
index 0000000000..ada4afd426
--- /dev/null
+++ b/third_party/python/ply/example/classcalc/calc.py
@@ -0,0 +1,165 @@
+#!/usr/bin/env python
+
+# -----------------------------------------------------------------------------
+# calc.py
+#
+# A simple calculator with variables.   This is from O'Reilly's
+# "Lex and Yacc", p. 63.
+#
+# Class-based example contributed to PLY by David McNab
+# -----------------------------------------------------------------------------
+
+import sys
+sys.path.insert(0, "../..")
+
+if sys.version_info[0] >= 3:
+    raw_input = input
+
+import ply.lex as lex
+import ply.yacc as yacc
+import os
+
+
+class Parser:
+    """
+    Base class for a lexer/parser that has the rules defined as methods
+    """
+    tokens = ()
+    precedence = ()
+
+    def __init__(self, **kw):
+        self.debug = kw.get('debug', 0)
+        self.names = {}
+        try:
+            modname = os.path.split(os.path.splitext(__file__)[0])[
+                1] + "_" + self.__class__.__name__
+        except:
+            modname = "parser" + "_" + self.__class__.__name__
+        self.debugfile = modname + ".dbg"
+        self.tabmodule = modname + "_" + "parsetab"
+        # print self.debugfile, self.tabmodule
+
+        # Build the lexer and parser
+        lex.lex(module=self, debug=self.debug)
+        yacc.yacc(module=self,
+                  debug=self.debug,
+                  debugfile=self.debugfile,
+                  tabmodule=self.tabmodule)
+
+    def run(self):
+        while 1:
+            try:
+                s = raw_input('calc > ')
+            except EOFError:
+                break
+            if not s:
+                continue
+            yacc.parse(s)
+
+
+class Calc(Parser):
+
+    tokens = (
+        'NAME', 'NUMBER',
+        'PLUS', 'MINUS', 'EXP', 'TIMES', 'DIVIDE', 'EQUALS',
+        'LPAREN', 'RPAREN',
+    )
+
+    # Tokens
+
+    t_PLUS = r'\+'
+    t_MINUS = r'-'
+    t_EXP = 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(self, t):
+        r'\d+'
+        try:
+            t.value = int(t.value)
+        except ValueError:
+            print("Integer value too large %s" % t.value)
+            t.value = 0
+        # print "parsed number %s" % repr(t.value)
+        return t
+
+    t_ignore = " \t"
+
+    def t_newline(self, t):
+        r'\n+'
+        t.lexer.lineno += t.value.count("\n")
+
+    def t_error(self, t):
+        print("Illegal character '%s'" % t.value[0])
+        t.lexer.skip(1)
+
+    # Parsing rules
+
+    precedence = (
+        ('left', 'PLUS', 'MINUS'),
+        ('left', 'TIMES', 'DIVIDE'),
+        ('left', 'EXP'),
+        ('right', 'UMINUS'),
+    )
+
+    def p_statement_assign(self, p):
+        'statement : NAME EQUALS expression'
+        self.names[p[1]] = p[3]
+
+    def p_statement_expr(self, p):
+        'statement : expression'
+        print(p[1])
+
+    def p_expression_binop(self, p):
+        """
+        expression : expression PLUS expression
+                  | expression MINUS expression
+                  | expression TIMES expression
+                  | expression DIVIDE expression
+                  | expression EXP expression
+        """
+        # print [repr(p[i]) for i in range(0,4)]
+        if p[2] == '+':
+            p[0] = p[1] + p[3]
+        elif p[2] == '-':
+            p[0] = p[1] - p[3]
+        elif p[2] == '*':
+            p[0] = p[1] * p[3]
+        elif p[2] == '/':
+            p[0] = p[1] / p[3]
+        elif p[2] == '**':
+            p[0] = p[1] ** p[3]
+
+    def p_expression_uminus(self, p):
+        'expression : MINUS expression %prec UMINUS'
+        p[0] = -p[2]
+
+    def p_expression_group(self, p):
+        'expression : LPAREN expression RPAREN'
+        p[0] = p[2]
+
+    def p_expression_number(self, p):
+        'expression : NUMBER'
+        p[0] = p[1]
+
+    def p_expression_name(self, p):
+        'expression : NAME'
+        try:
+            p[0] = self.names[p[1]]
+        except LookupError:
+            print("Undefined name '%s'" % p[1])
+            p[0] = 0
+
+    def p_error(self, p):
+        if p:
+            print("Syntax error at '%s'" % p.value)
+        else:
+            print("Syntax error at EOF")
+
+if __name__ == '__main__':
+    calc = Calc()
+    calc.run()