The idea for this post started on Aug 11, 2011, when I read Gregg’s post about choosing a scripting language for 3DScript, the CGM interactive test bed. That article had a lot of good ideas, but I feel like it kind of missed the point regarding Lisp/Scheme/Functional Programming. He used a do loop to try to make the point that the syntax is rather goofy. The reason scheme came up at all is that it is used as a scripting language for acis3dt.exe our 3D ACIS Modeler Test application.
I actually agree that the syntax for a do loop is goofy. However, learning about Lisp (and the lispy features of perl, see http://hop.perl.plover.com/) has made me a much better programmer than I would otherwise be. In some ways, this thesis is older than the hills. To illustrate this, Google various subjects surrounding Lisp, Functional Programming, etc., for example, map-reduce. When I talk with other programmers, I get the feeling that the message bears repeating.
So please bear with me while I sketch a few specifics. Also, feel free to add your own in the comments:
- Referential transparency makes things a lot easier to reason about. Put another way: it is much easier to deal with C/C++ code that doesn’t modify global and static variables.
- The best way to speed up code is to get a smarter algorithm.
- Writing programs as compositions of simple (but high order functions), makes it much easier to reason about them:
- There are a few functional programming clichés that often help in dramatically speeding things up
- Memoization
- Make the algorithm lazy
- Mathematical proofs are very easily given in terms of induction/recursion
- The literature on Lisp has lots of discussion about how you can convert between recursion and iteration.
- Thinking about classes in terms of closures is helpful to me.
A common anti-pattern in legacy code is monolithic and large functions which give a detailed to do list. Typically, I end up extracting functions from the huge monster, turning them into classes, and then parameterizing their behavior. This is really almost the same thing as taking a code snippet, making a closure over the variables you need to encapsulate, etc.
C/C++ still tends to be ubiquitous because:
(a) So many system libraries are written in C or C++
(b) Well written C++ can be very fast
However, C-style languages don’t lend themselves to simple and concise reasoning about code. If there were a well-established Lisp with a good linker, it might eat C’s lunch.
Here's a cartoon on the subject http://imgs.xkcd.com/comics/lisp.jpg
What do you think?
