+ (frob-do-body varlist endlist body 'let 'psetq 'do-anonymous (gensym)))
+\f
+;;;; GENSYM tricks
+
+;;; 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))))))))
+
+;;; Automate an idiom often found in macros:
+;;; (LET ((FOO (GENSYM "FOO"))
+;;; (MAX-INDEX (GENSYM "MAX-INDEX-")))
+;;; ...)
+;;;
+;;; "Good notation eliminates thought." -- Eric Siggia
+;;;
+;;; Incidentally, this is essentially the same operator which
+;;; _On Lisp_ calls WITH-GENSYMS.
+(defmacro with-unique-names (symbols &body body)
+ `(let ,(mapcar (lambda (symbol)
+ (let* ((symbol-name (symbol-name symbol))
+ (stem (if (every #'alpha-char-p symbol-name)
+ symbol-name
+ (concatenate 'string symbol-name "-"))))
+ `(,symbol (sb!xc:gensym ,stem))))
+ symbols)
+ ,@body))
+
+;;; Return a list of N gensyms. (This is a common suboperation in
+;;; macros and other code-manipulating code.)
+(declaim (ftype (function (index &optional t) (values list &optional))
+ make-gensym-list))
+(defun make-gensym-list (n &optional name)
+ (when (eq t name)
+ (break))
+ (if name
+ (loop repeat n collect (sb!xc:gensym (string name)))
+ (loop repeat n collect (sb!xc:gensym))))