(module why mzscheme
  (require "../private/headelts.ss"
           "../private/util.ss"
           (lib "servlet.ss" "web-server"))
  (provide interface-version timeout start)
  (define interface-version 'v1)
  (define timeout +inf.0)
  (define (start initial-request)
    (report-errors-to-browser send/finish)
    `(html
      (head ,hd-css ,@hd-links (title "Why DrScheme?"))
      (body
       (h1 "Why DrScheme?")
       "Teaching introductory computing courses with Scheme, or any other"
       " functional programming language, facilitates many conceptual tasks"
       " and greatly enhances the appeal of computer science. Specifically,"
       " students can implement many interesting programs with just a small"
       " subset of the language. The execution of a functional program can be"
       " explained with simple reduction rules that students mostly know from"
       " secondary school.  Interactive implementations allow for quick"
       " feedback to the programmers andmake the development of small"
       " functions a pleasant experience."
       (p)
       "Unfortunately, the poor quality of the available environments for"
       " functional languages negates these advantages.  Typical"
       " implementations accept too many definitions, that is, definitions"
       " that are syntactically well-formed in the sense of the full language"
       " but meaningless for beginners. The results are inexplicable behavior,"
       " incomprehensible run-time errors, or confusing type error messages."
       " The imperative nature of read-eval-print loops often introduces"
       " subtle bugs into otherwise perfect program developments. Scheme, in"
       " particular, suffers from an adherence to Lisp's output traditions,"
       " which often produces confusing effects. In many cases students,"
       " especially those familiar with commercial C++ environments, mistake"
       " these problems for problems with the functional approach and reject"
       " the approach itself."
       (p)
       "To overcome this obstacle, we have developed a new programming"
       " environment for Scheme. It fully integrates a (graphics-enriched)"
       " editor, a multi-lingual parser that can process a hierarchy of"
       " syntactically restrictive variants of Scheme, a functional"
       " read-eval-print loop, and an algebraically sensible printer.  The"
       " environment catches the typical syntactic mistakes of beginners and"
       " pinpoints the exact source location of run-time exceptions.  The new"
       " programming environment also provides an algebraic stepper and a"
       " static debugger. The former reduces Scheme programs, including"
       " programs with assignment and control effects, to values (and"
       " effects).  The static debugger infers what set of values an"
       " expression may produce and how values flow from expressions into"
       " variables. It exposes potential safety violations and, upon demand"
       " from the programmer, explains its reasoning by drawing value"
       " flowgraphs over the program text.  Preliminary experience with the"
       " environment shows that students find it helpful and that they greatly"
       " prefer it to shell-based or Emacs-based systems."
       (p)
       "A paper that discusses DrScheme in more detail is available in the"
       " paper: "
       (a ([href "http://www.ccs.neu.edu/scheme/pubs#jfp01-fcffksf"]
           [target "_top"])
          "DrScheme: A Programming Environment for Scheme") "."))))