Lexical scope, in particular, is very easy to implement. Call/cc or exceptions are a bit tougher, but it can be done. And all defaults take is a bit of extensio

Lexical scope, in particular, is very easy to implement. Call/cc or exceptions are a bit tougher, but it can be done. And all defaults take is a bit of extension to the lambda. In fact, defaults can be added atop the language with a macros, as can keyword arguments. Macro expanders are a bit harder to write than the functionality itself, however. Especially if you want a good one.