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prolog in scheme

    We tried using the query system in "Structure & Interpretation" in our
    freshman class last year and found it wanting in some respects.  (1) It
    doesn't handle disjunctions unless the disjuncts contain the same variables.
    (2) It is extremely slow. We were using it in TI's PC Scheme on AT's.  We
    gave some very simple logic programming problems (e.g. the standard kinship
    relations) and found that the students we spending 10 or 15 minutes waiting
    for the query system to finish!  They found this very frustrating.

(1) GJS consistently updates the query language and fixes versions as bugs
appear.  You should get in touch with him, the bug may have been

(2) I have observed this also on MacScheme.  I don't know about PC
Scheme, but in the case of MacScheme the reason is probably that
streams have no interpreter support, they are written in scheme.  This
is unlike MIT Scheme, for which the code was originally written.  PC
Scheme may have the same problem.  While it is not blindingly fast on
our machines at MIT, it only becomes slow with relatively complicated
programs, and is adequately fast for the class.  10 or 15 mins. is way
longer than I've ever seen it take while solving the S&ICP problems.