According to Transient documentation:

"The command can also be a closure or lambda expression, but that should only be used for dynamic transients whose suffixes are defined when the prefix command is invoked. See information about the :setup-children function"

So according to that I tried the following:

(defun set-children (children) '((1 transient-suffix (:key "o" :command normal-func)) ;; OK (1 transient-suffix (:key "k" :description (lambda () "All ok") :command (lambda (message "hey")))))) (transient-define-prefix my-transient () ["Description" :setup-children set-children]) 

I'm getting (wrong-type-argument (command symbol) (lambda nil "hey"))

So it seems that it only accepts symbols

Any ideas? thanks in advance