2015年12月13日日曜日 2時21分21秒 UTC+9 Alex Knauth:
> > On Dec 12, 2015, at 9:18 AM, Taro Annual <sagyo12341...@gmail.com> wrote:
>
> > In racket libraries, rackjure module looks usable.
> > But, rackjure's threading(~>) denys lambda.
> >
> > ----
> > #lang rackjure
> >
> >> (#fn(map sqr %) '(1 2))
> > '(1 4)
> >> (~> '(1 2) #fn(map sqr %))
> > [Error] lambda: not an identifier, identifier with default, or keyword in:
> > (1 2)
>
> This will work if you use (~> '(1 2) [#fn(map sqr %)]).
>
> Or, if you use the `~>` from the point-free package instead, (~> '(1 2)
> #fn(map sqr %)) works fine. In the point-free package, ~> is a function, so
> it works with values (i.e. functions) instead of not-quite-expressions.
>
> >> (define (sqrlst lst) (map sqr lst))
> >> (~> '(1 2) sqrlst)
> > '(1 4)
> > ----
> >
> > In this case, what is the suitable solution?
> > Thank you for reading.
> >
> > Taro
Thanks, Alex.
I'll use point-free and srfi/26 module.
#lang racket
(require point-free srfi/26)
(define (distance lst)
(~> lst
(cut map sqr <>)
(cut apply + <>)
sqrt))
> (distance '(3 4))
5
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