This is the clack-errors Reference Manual, version 0.2, generated automatically by Declt version 4.0 beta 2 "William Riker" on Tue Jul 15 04:34:32 2025 GMT+0.
The main system appears first, followed by any subsystem dependency.
clack-errorsError page middleware for Clack.
Fernando Borretti
LLGPL
# clack-errors
[](https://travis-ci.org/eudoxia0/clack-errors)
[](http://quickdocs.org/clack-errors/)


A clone of [better_errors](https://github.com/charliesome/better_errors)
for [Clack](https://github.com/fukamachi/clack).
By default, when Clack throws an exception when rendering a page, the server
waits for the response until it times out while the exception waits in the
REPL. This isn’t very useful. So now there’s this.
# Usage
This,
“‘lisp
(clack:clackup
  (funcall clack-errors:*clack-error-middleware*
           *my-clack-app*
           :debug t)
  :port 8000)))
“‘
will wrap your Clack up in the clack-errors middleware, start the server and
return a handler object.
By default, the middleware will show all information. In a production
environment, you’ll want to initialize this with the ‘:debug‘ parameter set to
NIL.
## Using a Custom Error Page
The middleware can be initialized with the ‘:fn‘ slot set to a lambda that takes
a condition as its argument and returns the HTML string to return to the client.
“‘lisp
(clack:clackup
  (funcall clack-errors:*clack-error-middleware*
    *app*
    :fn (lambda (condition) "500 Internal Server Error")))
“‘
# License
Copyright (c) 2013–2019 Fernando Borretti (eudoxiahp@gmail.com)
Licensed under the LLGPL License.
0.2
clack (system).
closer-mop (system).
local-time (system).
trivial-backtrace (system).
djula (system).
cl-ppcre (system).
src (module).
Modules are listed depth-first from the system components tree.
clack-errors/srcclack-errors (system).
clack-errors.lisp (file).
Files are sorted by type and then listed depth-first from the systems components trees.
clack-errors/src/clack-errors.lispsrc (module).
*clack-error-middleware* (special variable).
*dev-css-path* (special variable).
*highlight-css* (special variable).
*highlight-js* (special variable).
*prod-css-path* (special variable).
+backtrace-regex+ (special variable).
+dev-template+ (special variable).
+prod-template+ (special variable).
condition-name (function).
condition-slots (function).
parse-backtrace (function).
render (function).
render-prod (function).
slot-values (function).
split-backtrace (function).
Packages are listed by definition order.
clack-errorslack.middleware.clack.errors
common-lisp.
*clack-error-middleware* (special variable).
*dev-css-path* (special variable).
*highlight-css* (special variable).
*highlight-js* (special variable).
*prod-css-path* (special variable).
+backtrace-regex+ (special variable).
+dev-template+ (special variable).
+prod-template+ (special variable).
condition-name (function).
condition-slots (function).
parse-backtrace (function).
render (function).
render-prod (function).
slot-values (function).
split-backtrace (function).
Definitions are sorted by export status, category, package, and then by lexicographic order.
A regular expression to split backtraces
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