Welcome to the CHICKEN Scheme pasting service

(import string-interpolation)

(define BUILTINS '(x p d du dur r q l ln t exn e ch h c f g s ?))

(define (command? id) (or (memq id BUILTINS) (assq id command-table)))

;optional help, reuses "current help" when missing.
;
;say  statement "." means info, ";" means commentary,
;
;ask  query     "?" means a Y|N boolean, ":" means a *

(define-type say (string -> void))
(define-type ask (string #!rest string -> *))

(define-type evaluator (* -> void))

(define (dwim-dot-command form command? say ask evaluator)
  (and-let* ((hd (car form))
             (((symbol? hd)))
             ((nm (symbol->string hd))) )
    (if (not (positive? (string-length nm)))
        (false (say "Looking for a command or an expression but got nothing; #(form)"))
        (begin
          ;what's wrong
          (say "You began what might be a command w/ an invalid marker.")
          ;try common mistake(s) 1st. then a more generic ask
          (if (or (and (char=? #\. (string-ref rm 0))
                       (ask "Looks like you typed the `.', instead of the `,'. Fix it?"))
                  (ask "Did you mean a command? Maybe just typo'ed the marker?"
                       "A \"marker\" is the leading character used to signal a command."
                       "Here looking for a `,'."))
              ;then see if can extract a viable command w/ little effort
              (let ((cmd (string->symbol (substring nm 1))))
                (if (command? cmd)
                    ;then go for it w/o asking since exact spelling
                    (evaluator `(unquote ,cmd ,@(cdr form)))
                    ;else give up
                    ;not just a typo'ed marker. skip prefix & try again. then fail.
                    (false (say #"`#(cmd)' is not unrecognized as a command"))) )
              ;else give up
              (false (say "There isn't more help.")) ) ) ) ) )

(set! ##sys#user-form-parse-hook dwim-command)