typed-compose/typed-compose.rkt

;;; typed-compose.rkt
;;;
;;; Copyright 2020 Sergiu Ivanov <sivanov@colimite.fr>
;;;
;;; This program is free software: you can redistribute it and/or
;;; modify it under the terms of the GNU General Public License as
;;; published by the Free Software Foundation, either version 3 of the
;;; License, or (at your option) any later version.
;;;
;;; This program is distributed in the hope that it will be useful,
;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
;;; General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with this program.  If not, see
;;; <https://www.gnu.org/licenses/>.

#lang typed/racket

(require (for-syntax syntax/parse))

(module+ test
  (require typed/rackunit))

(: compose-n (All (a) (-> (-> a a) * (-> a a))))
(define (compose-n . funcs)
  (λ (x)
    (for/foldr ([x x]) ([f funcs])
      (f x))))

(module+ test
  (check-equal? ((compose-n add1 add1 add1) 3) 6))