lisp-pipe.rkt

; imperative style
(define-syntax (-> x)
  (let* ((sym (gensym))
         (arg (cdr (syntax-e x)))
         (lines (map (λ (f)
                        (if (identifier? f)
                            #`(set! #,sym (#,f #,sym))
                            #`(set! #,sym (#,@f #,sym))))
                     (cdr arg))))
         #`(let ((#,sym #,(car arg)))
                #,@lines
                #,sym)))

; full macro expansion
(define-syntax (-> x)
  (let ((arg (cdr (syntax-e x))))
        (foldl (λ (l r)
                  (if (identifier? l)
                      #`(#,l #,r)
                      #`(#,@l #,r)))
               (car arg) (cdr arg))))

; functional style
(define-syntax (-> x)
  (let* ((arg (cdr (syntax-e x)))
         (v (car arg))
         (fns (map (λ (f) (if (identifier? f) f
                          `(curry ,@f)))
                   (reverse (cdr arg)))))
        #`((compose #,@fns) #,v)))

; example:
; > (-> 2 sqrt (+ 1))
; 2.414213562373095