def eval(cls, *args):
obj = Expr.__new__(cls, *args)
#use dummy variables internally, just to be sure
nargs = len(args) - 1
expression = args[nargs]
funargs = [C.Symbol(arg.name, dummy=True) for arg in args[:nargs]]
#probably could use something like foldl here
for arg, funarg in zip(args[:nargs], funargs):
expression = expression.subs(arg, funarg)
funargs.append(expression)
obj._args = tuple(funargs)
return obj
