1 files changed, 152 insertions, 0 deletions
diff --git a/ext/ply/example/classcalc/calc.py b/ext/ply/example/classcalc/calc.py
new file mode 100644
index 000000000..b2f3f70f1
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+++ b/ext/ply/example/classcalc/calc.py
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+#!/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,"../..")
+
+import readline
+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", 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):
+        print "Syntax error at '%s'" % p.value
+
+if __name__ == '__main__':
+    calc = Calc()
+    calc.run()