Cannot post slack webhook url in common lisp - common-lisp

Question

I wanted to post slack webhook, but I get an error.
This works:
(defun post-slack ()
(drakma:http-request "https://hooks.slack.com/services/xxx"
:method :post
:content-type "application/json"
:parameters '(("payload" . "{\"username\":\"bot\",\"icon_emoji\":\":hatching_chick:\",\"text\":\"name: ~A \n email: ~A \n content: ~A \",\"as_user\":true}"))))
But this does not:
(defun post-slack (name email text)
(setq *payload* (format nil "{\"username\":\"bot\",\"icon_emoji\":\":hatching_chick:\",\"text\":\"<#U7RM4J8MR> name: ~A \n email: ~A \n text: ~A \",\"as_user\":true}" name email text))
(drakma:http-request "https://hooks.slack.com/services/xxx"
:method :post
:content-type "application/json"
:parameters '(("payload" . *payload*))))
This is my error:
The value
CAVEMAN-STUDY.CONTROLLER::*PAYLOAD*
is not of type
LIST
when binding SB-C::FAST
[Condition of type TYPE-ERROR]
Restarts:
0: [RETRY] Retry SLIME REPL evaluation request.
1: [*ABORT] Return to SLIME's top level.
2: [ABORT] abort thread (#<THREAD "new-repl-thread" RUNNING {1008826443}>)
Backtrace:
0: (FIND-IF-NOT #<FUNCTION (LAMBDA (DRAKMA::THING) :IN DRAKMA:HTTP-REQUEST) {22D088AB}> ("payload" . CAVEMAN-STUDY.CONTROLLER::*PAYLOAD*) :KEY #<FUNCTION CDR>)
1: (DRAKMA:HTTP-REQUEST #<PURI:URI https://hooks.slack.com/services/xxxx> :METHOD :POST :CONTENT-TYPE "application/json" :PARAMETERS ("payload" . CAVEMAN-STUDY.CON..
2: (SB-INT:SIMPLE-EVAL-IN-LEXENV (CAVEMAN-STUDY.CONTROLLER:POST-SLACK "aaa" "bbb" "ccc") #<NULL-LEXENV>)
3: (EVAL (CAVEMAN-STUDY.CONTROLLER:POST-SLACK "aaa" "bbb" "ccase"))
--more--
Please tell me how to fix it. Thanks!

Answer 1

You are passing (("payload" . *payload*)) to drakma:http-request,
and *payload* here is not evaluated, i.e., it is passed as a symbol,
not its value.
What you probably want is something like
(defun post-slack (name email text)
(let ((payload (format nil "..." ...)))
(drakma:http-request "https://hooks.slack.com/services/xxx"
:method :post
:content-type "application/json"
:parameters `(("payload" . ,payload)))))
Note that I replaced setq with let.
PS. You can also use (list (cons "payload" *payload*)) instead of `(("payload" . ,payload)) if you want to avoid backquote.

Answer 2

Since you're talking about Slack:
https://github.com/dptd/cl-slack (seems the most up to date and documented)
https://github.com/m0cchi/cl-slack
https://github.com/kkazuo/slack-client (in Quicklisp)
https://github.com/fiddlerwoaroof/slacker (most recent, no doc)
https://github.com/stryku/jasa (2017)
There are also more Slack bots.
I discovered these with quicksearch (I didn't know it was this handy).