The `~>` form provided by the `threading` package is a macro, and it treats
parentheses differently than a normal function would.
What you are looking for is probably the ~> *function*, provided by the
`point-free` package. That has simpler behavior, doing what you expect with
lambdas, curried functions, and other function expressions:
#lang racket
(require point-free)
(define (add2 x) (+ x 2))
(~> 1 add2) ; ok
(~> 1 (lambda (x) (+ x 2))) ; ok
(~> 1 (curry + 2)) ; ok
(define adder%
(class object%
(super-new)
(init-field x)
(define/public (incr) (lambda (y) (+ x y)))))
(define adder (new adder% [x 2]))
(send adder incr) ; ok
(~> 1 (send adder incr)) ; ok
> On Mar 31, 2018, at 9:24 PM, 若草春男 <whbug...@gmail.com> wrote:
>
> Hi, everyone.
>
> I think that racket threading macros can mix with expressions(lambda, curry,
> class, ...), but not in fact.
>
> #lang racket
> (require threading)
>
> (define (add2 x) (+ x 2))
> (~> 1 add2) ; ok
> (~> 1 (lambda (x) (+ x 2))) ; ng
> (~> 1 (curry + 2)) ; ng
>
> (define adder%
> (class object%
> (super-new)
> (init-field x)
> (define/public (incr) (lambda (y) (+ x y)))))
>
> (define adder (new adder% [x 2]))
> (send adder incr) ; ok
> (~> 1 (send adder incr)) ; ng
>
> Thanks,
> Haruo
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