> 2) RPN has a short syntax for them << a -> a 2 + >> The syntax is slightly different. What it should be is this << -> a << a 2 + >> >> The arrow introduces

> 2) RPN has a short syntax for them << a -> a 2 + >> The syntax is slightly different. What it should be is this << -> a << a 2 + >> >> The arrow introduces a binding form that captures the top n levels of the stack into n named local variables. (There's also a lower level implementation that forgoes the names in favor of a lookup-by-ordinal scheme that's a lot faster.) The other notable difference from what you might expect is that the lexical environment is not captured: Consider this function: << -> a << << a 2 + >> >> >> What it returns is a function object that looks like this, except that 'a' is a local variable reference rather than the global variable reference it looks like: << a 2 + >> Evaluating this results in an error, because while 'a' is represented as a local variable reference, the environment containing the local binding for 'a' is no longer available.