One thing I keep noticing is how similar Lisp and C++ are. Many Lispers, of course, would regard this as heresy, but to me it makes perfect sense. For example, take this passage from the book:

Many languages offer some form of macro, but Lisp macros are singularly powerful. When a file of Lisp is compiled, a parser reads the source code and sends its output to the compiler. Here’s the stroke of genius: the output of the parser consists of lists of Lisp objects. With macros, we can manipulate the program while it’s in this intermediate form between parser and compiler. If necessary, these manipulations can be very extensive.

Of course, the two languages aren’t exactly the same in this regard. C++ templates can’t be manipulated in the same way first-class C++ expressions can be; they are powerful, but really only give you full control over the type system. Being able to say lots of things about types in C++ will get you a long way, but not as far as Lisp macros will get you. Still, the similarities I think are striking, especially considering some of the newer techniques that have been discovered with C++ templates that let you go a bit beyond just the type system by doing some really obscure things with types.

A number of other similarities I think are significant; Lisp and C++ are the two languages with the best multi-paradigm support to which I’ve been exposed. Lisp tends to tilt functional, while C++ tilts procedural, but they both support all the major programming paradigms to practical degrees (although, to be fair, it would be easier to write an entirely procedural and/or object-oriented program in Lisp than it would be to write and entirely functional program in C++).

Anyway, just blurting some thoughts out loud while reading On Lisp.