There’s also the thrush function from the point-free package, which uses the argument order of the threading macro while providing the functional style of compose.
http://pkg-build.racket-lang.org/doc/point-free/index.html?q=thrush#%28def._%28%28lib._point-free%2Fmain..rkt%29._thrush%29%29 <http://pkg-build.racket-lang.org/doc/point-free/index.html?q=thrush#(def._((lib._point-free/main..rkt)._thrush))> > On Mar 14, 2015, at 15:35, Sean Kanaley <skana...@gmail.com> wrote: > > If "thread-through macro" refers to > "http://www.greghendershott.com/2013/05/the-threading-macro.html > <http://www.greghendershott.com/2013/05/the-threading-macro.html>" then I > recommend a functional alternative called "compose": > > (define print/cdr > (match-lambda > [(cons x xs) (print x) xs])) > > (define print-two > (compose print/cdr print/cdr)) > > The result is chained through naturally since the input and output type of > the lower level function are equal. > > For any number of printings > > (define (print-n n) > (for/fold ([print-n identity]) > ([i n]) > (compose print/cdr print-n))) > > (define print-two (print-n 2)) > > And for any number of anythings > > (define (iterate f n) > (for/fold ([chain identity]) > ([i n]) > (compose f chain))) > > (define print-two (iterate print/cdr 2)) > > > On Thu, Mar 12, 2015 at 2:25 PM, Don Green <infodeveloper...@gmail.com > <mailto:infodeveloper...@gmail.com>> wrote: > ;Design A: > ;Rating: 1 out of 10 > ;Poor because it uses set! > (define print-two > (lambda (f) > (print (first f)) > (set! f (rest f)) > (print (first f)) > (set! f (rest f)) > f)) > > (void (print-two '(1 2))) ;=> 12 > ;------------------------- > ;Design B: > ;Rating: 2 out of 10 > ;Better because it nests expressions to avoid using set! > ;Poor because it less readable. > (define print-two > (lambda (f) > (print (first f)) > (print (first (rest f))) > f)) > > (void (print-two '(1 2))) ;=> 12 > When called in situations that allow one expression only, enclose call within > a 'begin' expression. > ;------------------------- > ;Design C: > ;Rating: 3 out of 10 > ;Is this an even better design because it is more readable than nesting > expressions as in Design B above? > (define (print-two f) > (let* ([_ (print (first f))] > [f (rest f)] > [_ (print (first f))] > [f (rest f)]) > f)) > (void (print-two '(1 2))) ;=> 12 > ;------------------------- > My questions are: > "Can you recommend a better method?" > "Can you recommend a better method using 'define with lambda'?" > "Does your better method use a macro?" > "Does your better method use a thread-through macro?" If so, could you > please provide the definition of the thread-through macro. > THANKS! > > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users <http://lists.racket-lang.org/users> > > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users
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