Do any lisps support nested s-expression on their head? For example
((f 2) 3 4)
for which (f 2)
presumably evaluates to a fun
In those Lisps, which have single namespace for variables and functions, your expression is valid. These are called Lisp-1. Scheme and Clojure are examples of such Lisps.
In those Lisps, which have separate namespaces for variables and functions, your expression would be (funcall (f 2) 3 4)
. These are called Lisp-2. Common Lisp and Emacs Lisp are examples of such Lisps.
In Lisp-2 every symbol has a value slot and a function slot. To call a function, that is stored in a value slot you need to use funcall keyword.
See more on this issue: http://www.dreamsongs.com/Separation.html
Edit: Thanks to Rainer Joswig i corrected the answer.