Mel Reams

Nerrrrd

Scheme tip of the day

Get Racket. Technically the racket IDE is for the Racket language, but it works just fine with scheme if you put “#lang scheme” (minus the quotes) at the top of your .scm file. The thing I really love about Racket is the debugger. You can actually step through your scheme code instead of just littering it with (display <blah>)! So much easier!

SICP: first impressions

Not so long ago I decided to try working my way through Structure and Interpretation of Computer Programs, hereafter referred to as SICP because that’s an awful lot of typing. Why SICP? Because I hear it will make me a better programmer and because I’ve heard about it enough times that I want to know what I’m missing :)

Thanks to the wonders of the internets, you can get the book at the link above and MIT-Scheme or SCM scheme. If you’re running windows like me, I don’t so much recommend MIT-Scheme. I have heard that it’s the only one you can do all of the exercises from SICP in (I haven’t gotten far enough into the book yet to see if that’s true, but I’ll let you all know when I do), but the documentation for it is kind of painful and in general I’d rather take up cottage cheese sculpture than learn emacs.

SCM is much less painful to run once you get it installed, but that isn’t as easy as it looks. The quick start for windows section currently says to install slib-3b4-1.exe and then scm-5f2-1.exe, but that’s the wrong version of slib. You want slib-3b5-1.exe from http://people.csail.mit.edu/jaffer/SLIB.html, then you can install scm successfully. After that make sure scm scheme has been added to your path, then you can use whatever editor you want to work with your scheme files and run them from the command line with scm -f <filename>

For an editor, I personally like Sublime, although I’ll be honest, I’m cheap and I think $70 is a bit steep for a text editor. It does have excellent plugin support though, as well as a much nicer interface than free editors like Notepad++.

If you decide to go with Sublime, I recommend installing Package Control and then the scheme package to add scheme syntax highlighting. Once you have package control installed, go to preferences->package control and click “Package Control: Install Package” in the menu that will pop up. It lags a little bit on my machine but in a second or two a new popup will appear that lists all the packages you can install. Search for scheme and install that package. Once you restart you’ll have scheme syntax highlighting and paren matching, which is pretty handy.

When you’re editing your scheme file, it will probably be helpful to know that you print to standard out with (display <arg>) and print a carriage return with (newline). You can skip printing your output if you use the MIT-Scheme interpreter, but then you’d have to use the MIT-Scheme interpreter :)

My workflow so far is edit in sublime, run the file with scm from the command line (scm -f <filename>, don’t forget), then look at the output and go back to sublime.

Now that the environment setup is out of the way, let’s talk about scheme. It’s been almost ten years since I touched any dialect of Lisp and it’s incredibly weird working with it again. Normally I write methods/functions from the top down, but scheme forces me to write them from the center out. It’s also pretty strange to work in a language with so little syntax. There’s almost nothing to scheme but a few basic functions and shit-ton of parens. It’s kind of beautiful, but compared to java’s creepy obsession with boilerplate it’s really, really weird. I don’t know yet if SICP will actually make me a better programmer, but it’s definitely forcing me to look at problems from a different perspective.

So far SICP has covered pretty basic parts of programming, but if it’s been a while since you used scheme I recommend plodding through the refresher. And check your work with google, there are a ton of solutions out there for all the exercises, including this handy wiki. There are a couple of tricky questions about normal-order and applicative-order in the first chapter that I got completely backwards the first time, so check your work and run an example to make sure you’ve got a handle on it.

Expect to hear a lot more about SICP from me in the future, I have plenty of chapters to go.

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