Scheme 9 from Empty Space

(Reimagined)

S9fES Reimagined is is a complete rewrite of most of the S9fES Scheme interpreter. The new interpreter is almost 100% compatible with the previous version. The main difference is that it is much faster.

Highlights

• the S9 system now uses a bytecode compiler and abstract machine (earlier versions used a tree walker)
• the S9 interpreter now uses shallow binding instead of deep binding; this means that
  – symbol lookup is now O(1) (was O(n log n))
  – closure creation is now O(n) (small n, was O(1))
• the compiler inlines most standard Scheme procedures and lambda-lifts functions when called immediately. That is, ((lambda (x) y) z) will not create a closure (unless Y uses SET!).
• the table of interned symbols is now a hash table instead of a list

Yes, this means that S9 Reimagined is much, much faster than the original S9. Check out the benchmarks if you haven't already!

Other Improvements

• strings can now contain \n (newline) escape sequences; although non-standard, a lot of code out there appears to use this
• CALL/CC is finally working properly and passes all Petrofsky tests; it is rather expensive, though, because the interpreter does not do CPS conversion
• The *LIBRARY-PATH* is now in list form (was a Unix PATH-style string before)