Common Lisp

I manage dependencies with Quicklisp. I also write small scripts in Common Lisp. I don't want to pay for loading Quicklisp every time I run a script. (On principle; the load time is short.)

I need to manually tell ASDF where to find the systems pulled by Quicklisp. See the ASDF manual on controlling the registry for basics.

I developed these examples to put the basics into practice.

Encountered for version trivia-20230618-git in the Quicklisp dist.

I was loading trivia but not use-ing it. The patterns listed above, unprefixed, would cause errors.

Two solutions:

• (use-package :trivia) or equivalent, and don't namespace anything.
• (trivia:match <...> ((trivia:property <...>)))

In short, patterns must be namespaced just like macros and functions. trivia's macros don't pull them in automatically.

Use the empty pattern _ for a default branch.

For example:

(ql:quickload :trivia)
(trivia:match '(:a 1 :b 2 :c 3)
  ((trivia:plist :c 3 :a 1) 'ok))

OK

• libev: available as libev on Alpine 3.20.

 1  (define-condition malformed-log-entry-error (error)
 2    ((text :initarg :text :reader text)))
 3  
 4  (defun log-analyzer ()
 5    (handler-bind ((malformed-log-entry-error
 6                     #'(lambda (c)
 7                         (invoke-restart 'skip-log-entry))))
 8      (dolist (log (find-all-logs))
 9        (analyze-log log))))
10  
11  (defun analyze-log (log)
12    (dolist (entry (parse-log-file log))
13      (analyze-entry entry)))
14  
15  (defun parse-log-file (file)
16    (with-open-file (in file :direction :input)
17      (loop for text = (read-line in nil nil) while text
18            for entry = (restart-case (parse-log-entry text)
19                          (skip-log-entry () nil))
20            when entry collect it)))
21  
22  (defun parse-log-entry (text)
23    (if (well-formed-log-entry-p text)
24        (make-instance 'log-entry ...)
25        (restart-case (error 'malformed-log-entry-error :text text)
26          (use-value (value) value)
27          (reparse-entry (fixed-text) (parse-log-entry fixed-text)))))

Notice: Two functions establish restarts. Parse-log-file establishes one near line 18, and parse-log-entry establishes two near line 25.

The error call on line 25 is the only part of this code that can signal a condition. When that happens, all three restarts are available. The condition travels up the stack looking for a handler. If no function had one, we'd enter the debugger with at least our three custom restarts available. (Entering the debugger is a feature of ERROR. See WARN and SIGNAL.) But log-analyzer has a policy for a malformed-log-entry-error. It directly invokes the restart skip-log-entry. Handler-bind is used instead of handler-case; the latter would unwind the stack to log-analyzer. Control flow jumps to line 19, where the restart is defined. That expression returns nil, and the loop in parse-log-file continues as if nothing strange has happened.

Consider this case I just ([2025-08-07 Thu]) encountered.

I want a test macro to use package-internal streams to accumulate text. I declare them as special variables with defvar and bind them to nil. In the body of the macro, I can bind these variables to fresh streams for the duration of the macro body's execution. Then the macro user can call presupplied functions that, under the hood, write text to the fresh streams. Part of the macro looks like this:

`(let ((pass-stream (make-string-output-stream))
       (fail-stream (make-string-output-stream))
       (,result (eval ,@body)))
   ;; ...
   )

,@body is supposed to be where the macro user can call the presupplied functions. But let binds values in parallel. Therefore, during eval, the values of both stream variables are still nil.

Simply changing let to let* fixes the problem.

Say you're in CL-USER. Then this package definition:

(defpackage :foo
  (:use :cl)
  (:export :bar))

Interns :foo and :bar in CL-USER. That's probably not what you want. I'm not sure if :cl gets interned or if it already is. #: produces an uninterned symbol, so it's common to write:

(defpackage #:foo
  (:use :cl)
  (:export #:bar))

Install ecl-dev. Otherwise, ECL complains that it's "Unable to find include directory" when

1. Loading ~/quicklisp/setup.lisp or
2. Attempting to load an ASDF package

Guessing (1) is caused by (2).

Formatted like PATH. An empty string may appear once, either between colons or at the beginning or end of the string, to splice in inherited configuration (e.g. from Quicklisp). I haven't tested the splicing much.

This variable has worked on Alpine Linux with ECL 24.5.10 and SBCL 2.5.3.

ECL manual: Use :q at the debugger to return to the top-level loop. Use :rN to invoke restart N.

When in doubt, use the standard function invoke-restart, but remember: ECL keeps restart symbols in the SI package. So while the intuitive thing would be:

(invoke-restart 'restart-toplevel)

The correct invocation is:

(invoke-restart 'si::restart-toplevel)

Find correct symbols with, for example:

(mapcar #'restart-name (compute-restarts))

Many basics and good examples in ECL's manual.