The functions described here are defined in src/compiler.lisp and src/record.d and can be used to examine the internals of a compiled closure.

Closure name. The normal way to extract the name of a closure is FUNCTION-LAMBDA-EXPRESSION:

(defun my-plus-1 (x y) (declare (compile)) (+ x y))
⇒ MY-PLUS-1
(function-lambda-expression #'my-plus-1)
⇒ (LAMBDA (X Y) (DECLARE (COMPILE)) (+ X Y)) ;
⇒ T  ;
⇒ MY-PLUS-1
;; works only on closure objects
(sys::closure-name #'my-plus-1)
⇒ MY-PLUS-1

Closure bytecode. The actual bytecode vector (if you modify it, you can get a segfault when the function is executed):

(sys::closure-codevec #'my-plus-1)
⇒ #(0 0 0 0 2 0 0 0 6 3 174 174 51 2 53 25 3)

Closure constants. A closure can depend on external and internal values:

(let ((x 123) (y 456))
 (defun my-plus-2 (z) (declare (compile)) (+ x y z)))
⇒ MY-PLUS-2
(sys::closure-consts #'my-plus-2)
⇒ (#(Y 456 X 123 NIL) 3 1)

Use DISASSEMBLE to see how the constants are used.

Closure signature. Function SYS::SIGNATURE returns 8 values:

Mnemonic bytecodes. One can convert between numeric and mnemonic bytecodes ("LAP" stands for "Lisp Assembly Program"):

(multiple-value-bind (req-num opt-num rest-p key-p keyword-list
 allow-other-keys-p byte-list const-list)
 (sys::signature #'my-plus-1)
 (sys::disassemble-LAP byte-list const-list))
⇒ ((0 LOAD&PUSH 2) (1 LOAD&PUSH 2) (2 CALLSR 2 53) (5 SKIP&RET 3))
(sys::assemble-LAP (mapcar #'rest *))
⇒ (174 174 51 2 53 25 3)