reloading a required file

[hall@research.att.com (Bob Hall)]

    From: pshannon@iapetus.cv.nrao.edu (Paul Shannon)
    Date: Mon, 16 Aug 1993 01:59:52 GMT

    I have an mcl program in two files: a main file, and  a small one
    that defines a function that returns a view containing dialog items.

    After I tinker with the dialog items, I save the file, and re-evaluate
    all of the main file.  

    I had hoped that the function call

	 (require 'rules-dialog-box)

    would detect that  rules-dialog-box.lisp had changed since last loaded,
    but it seems not to.  The only solution I can imagine at this point is
    to quit from mcl, and start from scratch.  There must be a better way.

You can easily implement a recompile-and-reload-if-necessary function
using the Common Lisp function FILE-WRITE-DATE to compare the time
the binary was written with the time the source file was written.
Many defsystems do something like this.

(DEFUN SIMPLE-RECOMPILE-AND-RELOAD-IF-OUT-OF-DATE (SRCFILE-NO-EXTENSION)
  "Assumes you want the binary to be in the same directory with .fasl
   extension.  You can parameterize this if desired."
  (LET* ((SRC (FORMAT NIL "~a.lisp" SRCFILE-NO-EXTENSION))
         SRCDATE
         (BIN (FORMAT NIL "~a.fasl" SRCFILE-NO-EXTENSION))
         BINDATE)
    (WHEN (AND (PROBE-FILE SRC)
       	       (OR (NOT (PROBE-FILE BIN))
                   (NULL (SETQ SRCDATE (FILE-WRITE-DATE SRC)))
                   (NULL (SETQ BINDATE (FILE-WRITE-DATE BIN)))
                   (> SRCDATE BINDATE)))
      (COMPILE-FILE SRC :OUTPUT-FILE BIN)
      (LOAD BIN)))) ;;in a defsystem, you'd put the LOAD outside the WHEN.

You can even add your own require-like functionality by (e.g.) binding a flag
when your rules-dialog-box file is loaded, then adding a check in the
above function for whether the flag is boundp.

While there may be an MCL-native way to do this, the approach above is
portable across Common Lisps (assuming you parameterize correctly for
file naming conventions).

-- Bob