First, the usual disclaimer:

That said, I've run the latest version of PLT Scheme on two sets of benchmarks:
  • Benchmarks in the PLT sources – vs. Bigloo, Chicken, Gambit, Guile, Ikarus, Larceny, MIT Scheme, and Scheme48; safe operations and generic arithmetic only
The second set is why I started running benchmarks. Fixnum-/flonum-specific arithmetic and unsafe operations are new in PLT Scheme 4.2.4. The benchmark results suggest that the new operations in PLT Scheme offer roughly the same performance benefits as in Bigloo and Gambit. There's room for improvement, but it's a good first cut. For the other results: PLT Scheme is rarely the fastest implementation on a given benchmark. For most purposes, though, it's in the same ballpark – except for programs that spend all their time capturing and invoking continuations. It's fun to run benchmarks occasionally. Now, back to working on language design, libraries, documentation, usability...


PLT Scheme v4.2.4

PLT Scheme version 4.2.4 is now available from

  • The scheme/flonum and scheme/fixnum libraries provide flonum- and fixnum-specific operations. In the case of flonum-specific operations, the JIT compiler can recognize combinations of operations (including local bindings) and improve performance by "unboxing" intermediate results.
  • The scheme/unsafe/ops library provides arithmetic and other operations that are implemented without dynamic checks. Avoiding checks can sometimes improve performance, but at the expense of safety.
  • 2htdp/universe: We have severed the connection between universe and an image library and made a few other, minor changes. Most programs will now have to change to require the htdp/image library explicitly. For the full details, see the new Porting World Programs section of the documentation.
  • The 2htdp/image library continues to grow. In this release, it is supported by 2htdp/universe, equality changed to be based on how the images are drawn, cropping and curves were added, and support for more kinds of pens were added.
  • htdp/world: The old world teachpack remains deprecated. HtDP/2e exclusively uses the new 2htdp/universe library. For backwards compatibility, the world teachpack will remain in the distribution until the coming summer.
  • The scheme/class library now provides this%, which refers to the class of the current object (i.e. this).
  • scheme/generator has convenient functions for infinite generators, and for converting a generator to a sequence for iteration.
  • PLT Scheme's add-on directory can be customized by the $PLTADDONDIR environment variable or --addon/-A command-line flags. This controls where downloaded Planet packages and their compiled Scribble documentation are installed.
  • Additional extensions include: saving errno in foreign calls, much improved sort speed, normalized results from procedure-arity, and more.


Scheme Videos (Lectures and Talks)

Scheme Videos (Lectures and Talks)

(thanks to Geoffrey Knauth and Hari)

Following a mailing-list request, it turns out that there are quite a lot of Scheme-related lectures and talks floating around out there in video format. The following list was compiled by Geoffrey Knauth, with contributions from Hari and Michael Sperber, and at least one insertion from me, right at the front.