tk's bits

I went ahead and made the continuation style evaluator more uniform in the handling of syntax expressions.

I also moved the recognition test for syntax expressions up into the body of ev-c. This makes evsyntax-c a procedure that handles only syntax expressions. The interpreter is much faster now. I attribute this to the still primitive CONSing of arguments in a procedure call. The vast majority of procedure calls are by name, and the redundant test bypasses the call to evsyntax-c. This removes two levels of internal interpreter calls for each interpreted procedure call. The new code adds a redundant lookup only for syntax expressions. The lookup was already redundant when interpretation of procedure calls involved evsyntax-c.

    (syntax?
      (lambda (exp env)
        (eq? (first (bound-value (lookup (car exp) env))) prim-syntax-mark)))

    (ev-c
      (lambda (exp env c)
        (cond
          ((constant? exp) (evconst-c exp env c))
          ((symbol? exp) (evvar-c exp env c))
          ((syntax? exp env) (evsyntax-c exp env c))
          (#t (evcall-c exp env c)))))

    (evsyntax-c
      (lambda (exp env c)
        (evsyntaxc-c (bound-value (lookup (car exp) env)) exp env c)))

    (evsyntaxc-c
      (lambda (cmddef exp env c)
        (cond
          ((eq? (second cmddef) 'quote) (evquote-c exp env c))
          ((eq? (second cmddef) 'cond) (evcond-c exp env c))
          ((eq? (second cmddef) 'set!) (evset-c exp env c))
          ((eq? (second cmddef) 'letrec) (evletrec-c exp env c))
          ((eq? (second cmddef) 'lambda) (evlambda-c exp env c))
          (#t (undefined-c exp env c)))))

This entry was posted on Sunday, March 15th, 2009 at 8:33 pm and is filed under Lisp/Scheme. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.