Evaluating Medley compatibility with Practical Common Lisp code: Chapter 19 #1613

pamoroso · 2024-03-24T11:57:37Z

pamoroso
Mar 24, 2024
Collaborator

Chapter 19. Beyond Exception Handling: Conditions and Restarts

This is the continuation of the work on issue #609. To evaluate the compatibility of Medley Common Lisp with ANSI Common Lisp I'm testing on Medley the code of Peter Seibel's book Practical Common Lisp.

Issues

While working on chapter 19 I bumped into an error hinting at a missing loop feature. Before rewriting the code without loop or reporting an issue I want to make sure there's indeed a problem with loop.

Code

This is the first part of the code I'm evaluating at a XCL Exec, which adds some definitions and calls missing from the chapter:

(define-condition malformed-log-entry-error (error)
  ((text :initarg :text :reader text)))

(defun well-formed-log-entry-p (text)
  (not (search "MALFORMED" text)))

(defclass log-entry ()
  ((message :initarg :message :accessor message)))

(defun parse-log-entry (text)
  (if (well-formed-log-entry-p text)
    (make-instance 'log-entry :message text)
    (error 'malformed-log-entry-error :text text)))

(parse-log-entry "Well formed")

(parse-log-entry "MALFORMED")

(defun create-log-file (file)
  (with-open-file (s file :direction :output :if-exists :supersede)
    (dotimes (i 10)
      (format s "~&Log message ~a~%" i))
    (format s "~&MALFORMED~%")))

(create-log-file "pclchap19.log")

(defun parse-log-file (file)
  (with-open-file (in file :direction :input)
    (loop for text = (read-line in nil nil) while text
       for entry = (handler-case (parse-log-entry text)
                     (malformed-log-entry-error () nil))
       when entry collect it)))

Session transcript

And here is a session leading to an unprocessed loop form tail error:

2/8> (define-condition malformed-log-entry-error (error)
  ((text :initarg :text :reader text)))
MALFORMED-LOG-ENTRY-ERROR
2/9> 

2/9> (defun well-formed-log-entry-p (text)
  (not (search "MALFORMED" text)))
WELL-FORMED-LOG-ENTRY-P
2/10> 

2/10> (defclass log-entry ()
  ((message :initarg :message :accessor message)))
LOG-ENTRY
2/11> 

2/11> (defun parse-log-entry (text)
  (if (well-formed-log-entry-p text)
    (make-instance 'log-entry :message text)
    (error 'malformed-log-entry-error :text text)))
PARSE-LOG-ENTRY
2/12> 

2/12> (parse-log-entry "Well formed")
#<LOG-ENTRY 124,140174>
2/13> 

2/13> (parse-log-entry "MALFORMED")
Serious condition MALFORMED-LOG-ENTRY-ERROR occurred.

2/14> 

2/14> (defun create-log-file (file)
  (with-open-file (s file :direction :output :if-exists :supersede)
    (dotimes (i 10)
      (format s "~&Log message ~a~%" i))
    (format s "~&MALFORMED~%")))
CREATE-LOG-FILE
2/15> 

2/15> (create-log-file "pclchap19.log")
NIL
2/16> 

2/16> (defun parse-log-file (file)
  (with-open-file (in file :direction :input)
    (loop for text = (read-line in nil nil) while text
       for entry = (handler-case (parse-log-entry text)
                     (malformed-log-entry-error () nil))
       when entry collect it)))
Loop form tail (FOR ENTRY = (HANDLER-CASE (PARSE-LOG-ENTRY TEXT) (MALFORMED-LOG-ENTRY-ERROR NIL NIL)) WHEN ENTRY COLLECT IT) remained unprocessed.

2/17>

Are there any problems with this code? Is this a loop issue?

masinter · 2024-03-25T15:44:53Z

masinter
Mar 25, 2024
Maintainer

I tried the same script in sbl without problem, so I think this might be a problem with the Medley cl:loop not handling nested iterations.

(Whether in the sacla implementation or my result of loading that into Medley, I don't know.)

I didn't see a simple fix, so I'd suggest an issue. I got with-hash-table-iterator working but with-package-iterator is harder and I might put it on the shelf.

0 replies

pamoroso · 2024-03-25T16:18:12Z

pamoroso
Mar 25, 2024
Collaborator Author

I opened issue #1614. Since the two loop calls of the code are incidental to the chapter, which covers the condition system, I'll rewrite them.

0 replies

tfeb · 2024-03-25T17:29:03Z

tfeb
Mar 25, 2024
Collaborator

loop doesn't do nested iteration, so that is not the problem.

I would have to think about this more than I can do on a phone, but I think that

(loop for ...
      while ...
      for ...
      ...)

may not be legal.

In particular this is because the syntax is

loop [name-clause] {variable-clause}* {main-clause}* ...

and while ... is one of the things under main clause in the syntax.

(And yes, that's stupid but this is loop whose entire purpose is to set traps for the unwary, and even the wary.)

So if that is the case this is just not legal CL, even though the error message is not helpful here.

However as I said I am reading all this on a phone.

0 replies

masinter · 2024-03-25T18:45:27Z

masinter
Mar 25, 2024
Maintainer

it's easy enough to turn (loop for ... for ... collect ...) into (loop for ... nconc (for ... collect ...)) and similarly with pairs of accumulators
do/do, maximize/max for collect/nconc

and sbcl supports it, but it's a DWIMish kind of thing to fix up non-conforming code.

0 replies

pamoroso · 2024-03-26T13:31:23Z

pamoroso
Mar 26, 2024
Collaborator Author

Code

I rewrote the loop calls using do* and added the usual missing definitions and calls. Before discussing the test session, here is the complete code of the sequence of expressions I evaluated at a XCL Exec:

(define-condition malformed-log-entry-error (error)
  ((text :initarg :text :reader text)))

(defun well-formed-log-entry-p (text)
  (not (search "MALFORMED" text)))

(defclass log-entry ()
  ((message :initarg :message :accessor message)))

(defun parse-log-entry (text)
  (if (well-formed-log-entry-p text)
    (make-instance 'log-entry :message text)
    (error 'malformed-log-entry-error :text text)))

(parse-log-entry "Well formed")

(parse-log-entry "MALFORMED")

(defun create-log-file (file)
  (with-open-file (s file :direction :output :if-exists :supersede)
    (dotimes (i 10)
      (format s "~&Log message ~a~%" i))
    (format s "~&MALFORMED~%")))

(create-log-file "pclchap19.log")

(defun parse-log-file (file)
  (with-open-file (in file :direction :input)
    (do* (result
          (text (read-line in nil nil) (read-line in nil nil))
          (entry (handler-case (parse-log-entry text)
                   (malformed-log-entry-error () nil))
                 (handler-case (parse-log-entry text)
                   (malformed-log-entry-error () nil))))
        ((not text) (nreverse result))
      (when entry (push entry result)))))

(parse-log-file "pclchap19.log")

(defun skip-log-entry (c)
  (invoke-restart 'skip-log-entry))

(defun parse-log-file (file)
  (with-open-file (in file :direction :input)
    (do* (result
          (text (read-line in nil nil) (read-line in nil nil))
          (entry (restart-case (parse-log-entry text)
                   (skip-log-entry () nil))
                 (restart-case (parse-log-entry text)
                   (skip-log-entry () nil))))
        ((not text) (nreverse result))
      (when entry (push entry result)))))

(parse-log-file "pclchap19.log")

(defun analyze-entry (entry)
  (format t "~&Analyzing entry: ~a~%" entry))

(analyze-entry "This is an entry")

(defun analyze-log (log)
  (dolist (entry (parse-log-file log))
    (analyze-entry entry)))

(analyze-log "pclchap19.log")

(defun find-all-logs ()
  (list "pclchap19.log"))

(defun log-analyzer ()
  (dolist (log (find-all-logs))
    (analyze-log log)))

(log-analyzer)

(defun log-analyzer ()
  (handler-bind ((malformed-log-entry-error
                  #'(lambda (c)
                      (invoke-restart 'skip-log-entry))))
    (dolist (log (find-all-logs))
      (analyze-log log))))

(log-analyzer)

(defun log-analyzer ()
  (handler-bind ((malformed-log-entry-error #'skip-log-entry))
    (dolist (log (find-all-logs))
      (analyze-log log))))

(log-analyzer)

(defun skip-log-entry (c)
  (let ((restart (find-restart 'skip-log-entry)))
    (when restart (invoke-restart restart))))

(defun parse-log-entry (text)
  (if (well-formed-log-entry-p text)
    (make-instance 'log-entry :message text)
    (restart-case (error 'malformed-log-entry-error :text text)
      (use-value (value) value)
      (reparse-entry (fixed-text) (parse-log-entry fixed-text)))))

(parse-log-entry "Well formed")

(parse-log-entry "MALFORMED") ; error raised instead of RESTART-CASE

(defun log-analyzer ()
  (handler-bind ((malformed-log-entry-error
                  #'(lambda (c)
                      (use-value
                       (make-instance 'malformed-log-entry :text (text c))))))
    (dolist (log (find-all-logs))
      (analyze-log log))))

(log-analyzer)

Issues

Evaluating the expressions pointed out a couple of issues. The first is there doesn't seem to be any way of interactively invoking restarts or using values from the debugger, not even in the break window's middle-click menu.

The other issue is an undefined function error which is likely a bug in the code and not a Medley problem.

Session transcript

Now let's go over the code and the issues in the transcript of the test session. The first group of expressions worked fine, including the intentionally unhandled error:

2/8> (define-condition malformed-log-entry-error (error)
  ((text :initarg :text :reader text)))
MALFORMED-LOG-ENTRY-ERROR
2/9> 

2/9> (defun well-formed-log-entry-p (text)
  (not (search "MALFORMED" text)))
WELL-FORMED-LOG-ENTRY-P
2/10> 

2/10> (defclass log-entry ()
  ((message :initarg :message :accessor message)))
LOG-ENTRY
2/11> 

2/11> (defun parse-log-entry (text)
  (if (well-formed-log-entry-p text)
    (make-instance 'log-entry :message text)
    (error 'malformed-log-entry-error :text text)))
PARSE-LOG-ENTRY
2/12> 

2/12> (parse-log-entry "Well formed")
#<LOG-ENTRY 124,140174>
2/13> 

2/13> (parse-log-entry "MALFORMED")
Serious condition MALFORMED-LOG-ENTRY-ERROR occurred.

2/14> 

2/14> (defun create-log-file (file)
  (with-open-file (s file :direction :output :if-exists :supersede)
    (dotimes (i 10)
      (format s "~&Log message ~a~%" i))
    (format s "~&MALFORMED~%")))
CREATE-LOG-FILE
2/15> 

2/15> (create-log-file "pclchap19.log")
NIL
2/16> 

2/16> (defun parse-log-file (file)
  (with-open-file (in file :direction :input)
    (do* (result
          (text (read-line in nil nil) (read-line in nil nil))
          (entry (handler-case (parse-log-entry text)
                   (malformed-log-entry-error () nil))
                 (handler-case (parse-log-entry text)
                   (malformed-log-entry-error () nil))))
        ((not text) (nreverse result))
      (when entry (push entry result)))))
PARSE-LOG-FILE
2/17> 

2/17> (parse-log-file "pclchap19.log")
(#<LOG-ENTRY 124,140170> #<LOG-ENTRY 124,140164> #<LOG-ENTRY 124,140160> #<LOG-ENTRY 124,140154> #<LOG-ENTRY 124,140150> #<LOG-ENTRY 124,140144> #<LOG-ENTRY 124,140140> #<LOG-ENTRY 124,140134> #<LOG-ENTRY 124,140130> #<LOG-ENTRY 124,140124>)
2/18> 

2/18> (defun skip-log-entry (c)
  (invoke-restart 'skip-log-entry))
SKIP-LOG-ENTRY
2/19> 

2/19> (defun parse-log-file (file)
  (with-open-file (in file :direction :input)
    (do* (result
          (text (read-line in nil nil) (read-line in nil nil))
          (entry (restart-case (parse-log-entry text)
                   (skip-log-entry () nil))
                 (restart-case (parse-log-entry text)
                   (skip-log-entry () nil))))
        ((not text) (nreverse result))
      (when entry (push entry result)))))

New FUNCTIONS definition for PARSE-LOG-FILE.
PARSE-LOG-FILE
2/20>

The next call broke into the debugger. The parse-log-file function sets up a restart but I couldn't find any way of invoking it interactively:

2/20> (parse-log-file "pclchap19.log")
In EVAL:
Serious condition MALFORMED-LOG-ENTRY-ERROR occurred.

2/21: ^

The next few expressions worked as expected:

2/22> (defun analyze-entry (entry)
  (format t "~&Analyzing entry: ~a~%" entry))
ANALYZE-ENTRY
2/23> 

2/23> (analyze-entry "This is an entry")
Analyzing entry: This is an entry
NIL
2/24> 

2/24> (defun analyze-log (log)
  (dolist (entry (parse-log-file log))
    (analyze-entry entry)))
ANALYZE-LOG
2/25>

Then a call to analyze-log broke into the debugger, again with no apparent way of invoking restarts:

2/25> (analyze-log "pclchap19.log")
In EVAL:
Serious condition MALFORMED-LOG-ENTRY-ERROR occurred.

2/26: ^

The next couple of expressions worked as expected:

2/27> (defun find-all-logs ()
  (list "pclchap19.log"))
FIND-ALL-LOGS
2/28> 

2/28> (defun log-analyzer ()
  (dolist (log (find-all-logs))
    (analyze-log log)))
LOG-ANALYZER
2/29>

But the call to log-analyzer broke into the debugger with no way of invoking restarts:

2/29> (log-analyzer)
In EVAL:
Serious condition MALFORMED-LOG-ENTRY-ERROR occurred.

2/30: ^

The next group of expressions worked fine:

2/31> (defun log-analyzer ()
  (handler-bind ((malformed-log-entry-error
                  #'(lambda (c)
                      (invoke-restart 'skip-log-entry))))
    (dolist (log (find-all-logs))
      (analyze-log log))))

New FUNCTIONS definition for LOG-ANALYZER.
LOG-ANALYZER
2/32> 

2/32> (log-analyzer)
Analyzing entry: #<LOG-ENTRY 124,140120>
Analyzing entry: #<LOG-ENTRY 124,140114>
Analyzing entry: #<LOG-ENTRY 124,140110>
Analyzing entry: #<LOG-ENTRY 124,140104>
Analyzing entry: #<LOG-ENTRY 124,140100>
Analyzing entry: #<LOG-ENTRY 124,140074>
Analyzing entry: #<LOG-ENTRY 124,140070>
Analyzing entry: #<LOG-ENTRY 124,140064>
Analyzing entry: #<LOG-ENTRY 124,140060>
Analyzing entry: #<LOG-ENTRY 124,140054>
NIL
2/33> 

2/33> (defun log-analyzer ()
  (handler-bind ((malformed-log-entry-error #'skip-log-entry))
    (dolist (log (find-all-logs))
      (analyze-log log))))

New FUNCTIONS definition for LOG-ANALYZER.
LOG-ANALYZER
2/34> 

2/34> (log-analyzer)
Analyzing entry: #<LOG-ENTRY 124,140044>
Analyzing entry: #<LOG-ENTRY 124,140040>
Analyzing entry: #<LOG-ENTRY 124,140034>
Analyzing entry: #<LOG-ENTRY 124,140030>
Analyzing entry: #<LOG-ENTRY 124,140024>
Analyzing entry: #<LOG-ENTRY 124,140020>
Analyzing entry: #<LOG-ENTRY 124,140014>
Analyzing entry: #<LOG-ENTRY 124,140010>
Analyzing entry: #<LOG-ENTRY 124,140120>
Analyzing entry: #<LOG-ENTRY 124,140114>
NIL
2/35> 

2/35> (defun skip-log-entry (c)
  (let ((restart (find-restart 'skip-log-entry)))
    (when restart (invoke-restart restart))))

New FUNCTIONS definition for SKIP-LOG-ENTRY.
SKIP-LOG-ENTRY
2/36> 

2/36> (defun parse-log-entry (text)
  (if (well-formed-log-entry-p text)
    (make-instance 'log-entry :message text)
    (restart-case (error 'malformed-log-entry-error :text text)
      (use-value (value) value)
      (reparse-entry (fixed-text) (parse-log-entry fixed-text)))))

New FUNCTIONS definition for PARSE-LOG-ENTRY.
PARSE-LOG-ENTRY
2/37> 

2/37> (parse-log-entry "Well formed")
#<LOG-ENTRY 124,140104>
2/38>

The parse-log-entry call that follows generated the error Serious condition MALFORMED-LOG-ENTRY-ERROR occurred.. Although the code is supposed to let the user interactively set a value via restart-case and use-value, the call didn't break into the debugger and there was no way of setting a value:

2/38> (parse-log-entry "MALFORMED")
Serious condition MALFORMED-LOG-ENTRY-ERROR occurred.

2/39>

Finally, the call to log-analyzer generated the error Undefined car of form TEXT. I didn't aexpect the error as I thought the text reader was taken care of in the definition of malformed-log-entry-error earlier in the code:

2/39> (defun log-analyzer ()
  (handler-bind ((malformed-log-entry-error
                  #'(lambda (c)
                      (use-value
                       (make-instance 'malformed-log-entry :text (text c))))))
    (dolist (log (find-all-logs))
      (analyze-log log))))

New FUNCTIONS definition for LOG-ANALYZER.
LOG-ANALYZER
2/40> (log-analyzer)
In IL:ERROR:
Undefined car of form
TEXT

2/41: ^

0 replies

masinter · 2024-03-26T23:39:07Z

masinter
Mar 26, 2024
Maintainer

there is a problem #821 which describes the situation. The decision of when to break and when to just stop is "empirical" and the numbers were made for a different time.
(SETQ IL:HELPTIME -1) will make all error conditions respond with a break on error. I'm not sure what the criteria should be, but we need a timer that has microsecond or nanosecond rather than millisecond resolution if we're going to use elapsed time as an input to the decision.

Secondly, once you are in a BREAK window, the "OK" command will prompt you for the "proceed" case. This doesn't explain the "undefined function TEXT" problem, but might reduce the number problems found during testing.

0 replies

pamoroso · 2024-03-27T13:06:04Z

pamoroso
Mar 27, 2024
Collaborator Author

The fix

I rerun the tests and the debugger's OK command let me invoke restarts interactively. Here is a screenshot of the debugger handling a restart and the transcript of the session up to but not including use-value:

Session transcript

NIL
2/8> (define-condition malformed-log-entry-error (error)
  ((text :initarg :text :reader text)))
MALFORMED-LOG-ENTRY-ERROR
2/9> 

2/9> (defun well-formed-log-entry-p (text)
  (not (search "MALFORMED" text)))
WELL-FORMED-LOG-ENTRY-P
2/10> 

2/10> (defclass log-entry ()
  ((message :initarg :message :accessor message)))
LOG-ENTRY
2/11> 

2/11> (defun parse-log-entry (text)
  (if (well-formed-log-entry-p text)
    (make-instance 'log-entry :message text)
    (error 'malformed-log-entry-error :text text)))
PARSE-LOG-ENTRY
2/12> 

2/12> (parse-log-entry "Well formed")
#<LOG-ENTRY 124,140174>
2/13> 

2/13> (parse-log-entry "MALFORMED")
Serious condition MALFORMED-LOG-ENTRY-ERROR occurred.

2/14> 

2/14> (defun create-log-file (file)
  (with-open-file (s file :direction :output :if-exists :supersede)
    (dotimes (i 10)
      (format s "~&Log message ~a~%" i))
    (format s "~&MALFORMED~%")))
CREATE-LOG-FILE
2/15> 

2/15> (create-log-file "pclchap19.log")
NIL
2/16> 

2/16> (defun parse-log-file (file)
  (with-open-file (in file :direction :input)
    (do* (result
          (text (read-line in nil nil) (read-line in nil nil))
          (entry (handler-case (parse-log-entry text)
                   (malformed-log-entry-error () nil))
                 (handler-case (parse-log-entry text)
                   (malformed-log-entry-error () nil))))
        ((not text) (nreverse result))
      (when entry (push entry result)))))
PARSE-LOG-FILE
2/17> 

2/17> (parse-log-file "pclchap19.log")
(#<LOG-ENTRY 124,140170> #<LOG-ENTRY 124,140164> #<LOG-ENTRY 124,140160> #<LOG-ENTRY 124,140154> #<LOG-ENTRY 124,140150> #<LOG-ENTRY 124,140144> #<LOG-ENTRY 124,140140> #<LOG-ENTRY 124,140134> #<LOG-ENTRY 124,140130> #<LOG-ENTRY 124,140124>)
2/18> 

2/18> (defun skip-log-entry (c)
  (invoke-restart 'skip-log-entry))
SKIP-LOG-ENTRY
2/19> 

2/19> (defun parse-log-file (file)
  (with-open-file (in file :direction :input)
    (do* (result
          (text (read-line in nil nil) (read-line in nil nil))
          (entry (restart-case (parse-log-entry text)
                   (skip-log-entry () nil))
                 (restart-case (parse-log-entry text)
                   (skip-log-entry () nil))))
        ((not text) (nreverse result))
      (when entry (push entry result)))))

New FUNCTIONS definition for PARSE-LOG-FILE.
PARSE-LOG-FILE
2/20> 

2/20> (parse-log-file "pclchap19.log")
In EVAL:
Serious condition MALFORMED-LOG-ENTRY-ERROR occurred.

2/21: OK
1 (SKIP-LOG-ENTRY) - Restart type: SKIP-LOG-ENTRY
2 (ABORT) - Unwind to ERRORSET
No - don't proceed 
Proceed how? Restart type: SKIP-LOG-ENTRY
(#<LOG-ENTRY 124,140120> #<LOG-ENTRY 124,140114> #<LOG-ENTRY 124,140110> #<LOG-ENTRY 124,140104> #<LOG-ENTRY 124,140100> #<LOG-ENTRY 124,140074> #<LOG-ENTRY 124,140070> #<LOG-ENTRY 124,140064> #<LOG-ENTRY 124,140060> #<LOG-ENTRY 124,140054>)
2/22> (defun analyze-entry (entry)
  (format t "~&Analyzing entry: ~a~%" entry))
ANALYZE-ENTRY
2/23> 

2/23> (analyze-entry "This is an entry")
Analyzing entry: This is an entry
NIL
2/24> 

2/24> (defun analyze-log (log)
  (dolist (entry (parse-log-file log))
    (analyze-entry entry)))
ANALYZE-LOG
2/25> 

2/25> (analyze-log "pclchap19.log")
In EVAL:
Serious condition MALFORMED-LOG-ENTRY-ERROR occurred.

2/26: OK
1 (SKIP-LOG-ENTRY) - Restart type: SKIP-LOG-ENTRY
2 (ABORT) - Unwind to ERRORSET
No - don't proceed 
Proceed how? Restart type: SKIP-LOG-ENTRY
Analyzing entry: #<LOG-ENTRY 124,140050>
Analyzing entry: #<LOG-ENTRY 124,140044>
Analyzing entry: #<LOG-ENTRY 124,140040>
Analyzing entry: #<LOG-ENTRY 124,140034>
Analyzing entry: #<LOG-ENTRY 124,140030>
Analyzing entry: #<LOG-ENTRY 124,140024>
Analyzing entry: #<LOG-ENTRY 124,140020>
Analyzing entry: #<LOG-ENTRY 124,140014>
Analyzing entry: #<LOG-ENTRY 124,140010>
Analyzing entry: #<LOG-ENTRY 124,140004>
NIL
2/27> (defun find-all-logs ()
  (list "pclchap19.log"))
FIND-ALL-LOGS
2/28> 

2/28> (defun log-analyzer ()
  (dolist (log (find-all-logs))
    (analyze-log log)))
LOG-ANALYZER
2/29> 

2/29> (log-analyzer)
In EVAL:
Serious condition MALFORMED-LOG-ENTRY-ERROR occurred.

2/30: OK
1 (SKIP-LOG-ENTRY) - Restart type: SKIP-LOG-ENTRY
2 (ABORT) - Unwind to ERRORSET
No - don't proceed 
Proceed how? Restart type: SKIP-LOG-ENTRY
Analyzing entry: #<LOG-ENTRY 124,140000>
Analyzing entry: #<LOG-ENTRY 124,140044>
Analyzing entry: #<LOG-ENTRY 124,140050>
Analyzing entry: #<LOG-ENTRY 124,140034>
Analyzing entry: #<LOG-ENTRY 124,140040>
Analyzing entry: #<LOG-ENTRY 124,140024>
Analyzing entry: #<LOG-ENTRY 124,140030>
Analyzing entry: #<LOG-ENTRY 124,140014>
Analyzing entry: #<LOG-ENTRY 124,140020>
Analyzing entry: #<LOG-ENTRY 124,140004>
NIL
2/31> (defun log-analyzer ()
  (handler-bind ((malformed-log-entry-error
                  #'(lambda (c)
                      (invoke-restart 'skip-log-entry))))
    (dolist (log (find-all-logs))
      (analyze-log log))))

New FUNCTIONS definition for LOG-ANALYZER.
LOG-ANALYZER
2/32> 

2/32> (log-analyzer)
Analyzing entry: #<LOG-ENTRY 124,140010>
Analyzing entry: #<LOG-ENTRY 124,140044>
Analyzing entry: #<LOG-ENTRY 124,140000>
Analyzing entry: #<LOG-ENTRY 124,140034>
Analyzing entry: #<LOG-ENTRY 124,140050>
Analyzing entry: #<LOG-ENTRY 124,140024>
Analyzing entry: #<LOG-ENTRY 124,140040>
Analyzing entry: #<LOG-ENTRY 124,140014>
Analyzing entry: #<LOG-ENTRY 124,140030>
Analyzing entry: #<LOG-ENTRY 124,140004>
NIL
2/33> 

2/33> (defun log-analyzer ()
  (handler-bind ((malformed-log-entry-error #'skip-log-entry))
    (dolist (log (find-all-logs))
      (analyze-log log))))

New FUNCTIONS definition for LOG-ANALYZER.
LOG-ANALYZER
2/34> 

2/34> (log-analyzer)
Analyzing entry: #<LOG-ENTRY 122,46774>
Analyzing entry: #<LOG-ENTRY 122,46770>
Analyzing entry: #<LOG-ENTRY 122,46764>
Analyzing entry: #<LOG-ENTRY 122,46760>
Analyzing entry: #<LOG-ENTRY 122,46754>
Analyzing entry: #<LOG-ENTRY 122,46750>
Analyzing entry: #<LOG-ENTRY 122,46744>
Analyzing entry: #<LOG-ENTRY 122,46740>
Analyzing entry: #<LOG-ENTRY 122,46734>
Analyzing entry: #<LOG-ENTRY 124,140010>
NIL
2/35> 

2/35> (defun skip-log-entry (c)
  (let ((restart (find-restart 'skip-log-entry)))
    (when restart (invoke-restart restart))))

New FUNCTIONS definition for SKIP-LOG-ENTRY.
SKIP-LOG-ENTRY
2/36> 

2/36> (defun parse-log-entry (text)
  (if (well-formed-log-entry-p text)
    (make-instance 'log-entry :message text)
    (restart-case (error 'malformed-log-entry-error :text text)
      (use-value (value) value)
      (reparse-entry (fixed-text) (parse-log-entry fixed-text)))))

New FUNCTIONS definition for PARSE-LOG-ENTRY.
PARSE-LOG-ENTRY
2/37> 

2/37> (parse-log-entry "Well formed")
#<LOG-ENTRY 124,140000>
2/38> 

2/38> (parse-log-entry "MALFORMED")
Serious condition MALFORMED-LOG-ENTRY-ERROR occurred.

2/39>

After evaluating (SETQ IL:HELPTIME -1) and executing the last call (parse-log-entry "MALFORMED"), I was able to invoke the use-value restart. But, once I selected the restart, the debugger didn't let me enter a value. When I typed the first character of the value the debugger immediately asked me for confirmation and, whatever I typed, the break window closed and the call completed.

Here is a transcript of this part of the session and a couple of screenshots:

2/41> (SETQ IL:HELPTIME -1)
-1
2/42> 

2/42> (parse-log-entry "MALFORMED")
In EVAL:
Serious condition MALFORMED-LOG-ENTRY-ERROR occurred.

2/43: OK
1 (USE-VALUE) - Use a different value
2 (REPARSE-ENTRY) - Restart type: REPARSE-ENTRY
3 (ABORT) - Unwind to ERRORSET
No - don't proceed 
Proceed how? Use a different value
NIL
2/44> REDO
In EVAL:
Serious condition MALFORMED-LOG-ENTRY-ERROR occurred.

2/45: OK
1 (USE-VALUE) - Use a different value
2 (REPARSE-ENTRY) - Restart type: REPARSE-ENTRY
3 (ABORT) - Unwind to ERRORSET
No - don't proceed 
Proceed how? Use a different value�? [confirm] �?
 [confirm] �? [confirm] �? [confirm] 
NIL
2/46> REDO
In EVAL:
Serious condition MALFORMED-LOG-ENTRY-ERROR occurred.

2/47: OK
1 (USE-VALUE) - Use a different value
2 (REPARSE-ENTRY) - Restart type: REPARSE-ENTRY
3 (ABORT) - Unwind to ERRORSET
No - don't proceed 
Proceed how? Use a different value�? [confirm] 
NIL
2/48> REDO
In EVAL:
Serious condition MALFORMED-LOG-ENTRY-ERROR occurred.

2/49: OK
1 (USE-VALUE) - Use a different value
2 (REPARSE-ENTRY) - Restart type: REPARSE-ENTRY
3 (ABORT) - Unwind to ERRORSET
No - don't proceed 
Proceed how? Use a different value�? [confirm] �?
 [confirm]

The only remaining issues are the undefined text function and use-value not accepting a value interactively.

0 replies

pamoroso · 2024-04-04T17:02:20Z

pamoroso
Apr 4, 2024
Collaborator Author

From the Medley 1.0 release notes on page 225 of the PDF:

Under the new error system, use-value and store-value no longer prompt for a value.

This may be why use-value doesn't allow entering a value. Why was such a behavior implemented back then?

0 replies

masinter · 2024-04-08T20:15:49Z

masinter
Apr 8, 2024
Maintainer

i'm not sure it was a 'feature'. Sounds more like "we couldn't implement it in time" but I'm not sure.
Certainly there are other shortfalls that are listed in the release notes.

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Evaluating Medley compatibility with Practical Common Lisp code: Chapter 19 #1613

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Chapter 19. Beyond Exception Handling: Conditions and Restarts

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