Is learning LISP useful at all these days? [closed]

Question

I picked up a LISP book at a garage sale the other day and was just wondering if it was worth spending some time on.

Answer 1

Yes. I'll stick to Common Lisp, here, though Scheme is also a superb language that has a lot to recommend it.

In Common Lisp, you have a largish multi-paradigm language that provides some things that either don't exist widely outside the Lisp family of languages, or are limited to CL and even more obscure/niche languages.

The first feature, which you can get in one way or another from CL, Scheme and quite a few other dialects, is a real macro system.

I say "real" because the system is much more complete, flexible and reliable than, say, C preprocessor macros. It's extremely difficult to get CPP macros to do even simple things (like swapping the values of two variables, or making a foreach construct) in a reliable fashion, but these are trivial with Lisp macros. This turns out to be a very powerful tool for introducing new abstractions and dispensing with "boilerplate" code.

The second feature, which is effectively limited to Common Lisp, is CLOS, the Common Lisp Object System. Despite the name, it's not a conventional OO system like that of Java with methods being part of a class's definition. Instead, it provides polymorphism through "generic functions" which are what methods are attached to, and by default allow you to do multiple dispatch.

I vastly prefer CLOS to the more usual approach to object orientation, as it makes a number of "patterns" (like the Visitor pattern) completely unneccessary and because extension of existing generic functions is so easy; others loathe it because it takes an extremely cavalier approach to encapsulation and because extension of generic functions becomes arguably too easy. Either way, CLOS is different enough that I think it's worth learning just for the different perspective it provides.

The third feature, which is available outside of Lisp but still fantastic if you've never experienced it before is dynamic, interactive programming. CL debuggers tend to be extremely powerful tools, and CL provides for dynamic definition and redefinition of functions, classes and methods, all of which dramatically improves one's ability to explore a problem, test solutions of that problem and its subproblems, and finally put together a program that works correctly and efficiently.

Lastly, for a lot of classes of problems, Lisp is a great practical language. It provides good performance (usually not as fast as C, but dramatically faster than most "scripting languages"), safety, automatic memory management, a decent "standard library" of functions and tremendous opportnities for easy extension.

Answer 2

It is worth learning for "mind-expansion" purposes but not so popular for building apps these days.

However, it is powerful, and mature, and there are fast and free compilers out there. So there is no reason not to choose it for a program if you like.

The way in which Lisp treats data structures and program structures the same offers amazing power which is worth understanding.

Its history is fascinating and it has shaped the world of computer science.

Be sure to check out Ableson and Sussman's Structure and Interpretation of Computer Programs at MIT OpenCourseware

Clojure: a Lisp on .NET and Java VMs

GNU CLISP.

CMU Common Lisp