+ (sb!xc:gensym (format nil "~A[~A]" name block-name))
+ (sb!xc:gensym name))))
+
+;;; Compile a version of BODY for all TYPES, and dispatch to the
+;;; correct one based on the value of VAR. This was originally used
+;;; only for strings, hence the name. Renaming it to something more
+;;; generic might not be a bad idea.
+(defmacro string-dispatch ((&rest types) var &body body)
+ (let ((fun (sb!xc:gensym "STRING-DISPATCH-FUN")))
+ `(flet ((,fun (,var)
+ ,@body))
+ (declare (inline ,fun))
+ (etypecase ,var
+ ,@(loop for type in types
+ ;; TRULY-THE allows transforms to take advantage of the type
+ ;; information without need for constraint propagation.
+ collect `(,type (,fun (truly-the ,type ,var))))))))