Why is this an error in in SBCL?

Question

Why is this an error in SBCL? How do you call a lambda passed to your function?

* (defun call-foo (foo) (foo))
; in: DEFUN CALL-FOO
;     (SB-INT:NAMED-LAMBDA CALL-FOO
;         (FOO)
;       (BLOCK CALL-FOO (FOO)))
;
; caught STYLE-WARNING:
;   The variable FOO is defined but never used.

; in: DEFUN CALL-FOO
;     (FOO)
;
; caught STYLE-WARNING:
;   undefined function: FOO
;
; compilation unit finished
;   Undefined function:
;     FOO
;   caught 2 STYLE-WARNING conditions

CALL-FOO

Answer 1

This is an introduction to Common Lisp: http://www.cs.cmu.edu/~dst/LispBook/

You might also want to read about FUNCALL.