README: Dean Wampler's Solutions to the SICP Exercises

Dean Wampler (dean@polyglotprogramming.com)

These are solutions for many of the SICP exercises, written in Scheme, Scala, and Clojure and driven by a unit testing library for each language. I didn't solve all the exercises. Also, I didn't solve some of the problems in all three languages (especially those that were proofs, extensions of previous exercises, etc.)

Feedback is welcome.

Running the Solutions

There is a simple Makefile that runs all the solutions. However, it appears that failed tests don't return $? = 1 for all the runtimes (?), so if a particular exercise solution fails, make won't exit.

For running individual script files, use the run.sh files in each language directory, e.g., if your current directory is scheme/ch02 and you want to run the Exercise 2.1 solution, then use ../run.sh ex2.1.scm.

Scheme Solutions

Most of the Scheme solutions use just the features learned up to that point. The only exceptions are a few exercises where I use output functions and the (set! ...) form before the book introduced them, in order to test the exercise results.

I use SchemeUnit as the XUnit tool and run the solutions using PLT Scheme, in particular the mzscheme interpreter. One thing I noticed about this version of scheme; there is no nil defined for empty lists, as used in the book.. I used (list) instead.

Scala Solutions

I'm a self-proclaimed Scala expert: Programming Scala ;) Hence, some of my solutions use idioms that haven't been introduced at that point in the book.

I use Scala v2.7.X and ScalaTest v1.0 to run the solutions. You'll need to add the scalatest-x.y.jar to the CLASSPATH. I invoke scala interactively, then load and execute files, e.g.,

scala -cp $SCALA_TEST_HOME/scalatest-1.0/scalatest-1.0.jar
scala> :load ex1.3.scala
Loading ex1.3.scala...
f: (Int,Int,Int)Int
import org.scalatest._
import org.scalatest.matchers._
defined module FSpec
Squaring top two of three integers
- should select the top two values, square them, and add the result

(I suppressed some of the output.)

Sometimes I define versions of functions for which JDK implementations already exist, e.g., abs (absolute).

Clojure Solutions

I'm a novice Clojure user, so some of the solutions may be naive!

I switched to the Clojure 1.1 release candidates midstream without difficulty. The exercises probably work fine with 1.0, too. I use the clojure.test package that comes with the distribution to write the exercises as unit tests. To run them, I invoke the REPL, load each exercise solution into the REPL, then run it using the following command:

(run-tests)

Note that (run-tests) runs all the tests that have been defined in the current REPL session, not just test(s) for the last-loaded solution.

As for my Scala solutions, sometimes I define versions of functions for which JDK or Clojure core implementations already exist, e.g., abs (absolute) and even?.