-;;; Given a function name, return the name for the BLOCK which
-;;; encloses its body (e.g. in DEFUN, DEFINE-COMPILER-MACRO, or FLET).
+;;; Signal an error unless NAME is a legal function name.
+(defun legal-fun-name-or-type-error (name)
+ (unless (legal-fun-name-p name)
+ (error 'simple-type-error
+ :datum name
+ :expected-type '(or symbol list)
+ :format-control "invalid function name: ~S"
+ :format-arguments (list name))))
+
+;;; Given a function name, return the symbol embedded in it.
+;;;
+;;; The ordinary use for this operator (and the motivation for the
+;;; name of this operator) is to convert from a function name to the
+;;; name of the BLOCK which encloses its body.
+;;;
+;;; Occasionally the operator is useful elsewhere, where the operator
+;;; name is less mnemonic. (Maybe it should be changed?)