(require '#:asdf)
(asdf:oos 'asdf:load-op '#:cffi)

(defpackage #:foo
  (:use #:cffi #:cl)
  (:shadow float)
  (:export float))

(in-package #:foo)

(defctype foo:float :float)

(eval-when (:compile-toplevel :load-toplevel :execute)
  (defmethod cffi:expand-to-foreign (value (type (eql 'foo:float)))
    `(coerce ,value 'single-float)))

(eval-when (:compile-toplevel :load-toplevel :execute)
  (format t "~s~%" (macroexpand-1 '(cffi:defcfun foreign-foo :void (in foo:float)))))