Hi Aai,
I see what you are saying, but I would say that implicitly inside f there is
some sort of "such that" syntax.
My motivation for asking for a "such that / where" construct is to create
computable math definitions, as in Haskell.
for example, if I want the set (or group):
{ x e. Sym(4) | order(x) = 4} (where Sym(4) is the symmetric group on 4 letters)
then, assuming I have a verb "sym" and a verb "order" I can do
(sym 4) where (4&=@:order)
Then it may just be possible to generate groups from group presentations (
http://en.wikipedia.org/wiki/Presentation_of_a_group)(I haven't figured out how
to do this, I am just thinking about it over the holidays)
> Date: Sat, 27 Dec 2014 08:46:12 +0100
> From: [email protected]
> To: [email protected]
> Subject: Re: [Jprogramming] "Such that" syntax in J
>
> Sorry for jumping in late.
>
> The Haskell expression you showed here is called a list comprehansion
> which can be easily formulated as
>
> map f xs
>
> and this is in J simply:
>
> f xs
>
>
>
>
>
>
>
> Jon Hough schreef op 26-12-14 om 17:04:
> > In Haskell (and other languages I'm sure) one can express the idea of "such
> > that" to denote one expression depending on another. In Haskell we can use
> > the syntax:
> >
> > [ f x | x <- xs ]
> >
> > which means
> > "the list of all f x
> > such that x is drawn from xs."
> >
> > So | is syntactically similar to the English "such that". (and very much
> > like | in mathematical sets)
> >
> > I would like to know if J has a construct to express the above Haskell code.
> >
> > Thanks,
> > Jon.
> >
> > ----------------------------------------------------------------------
> > For information about J forums see http://www.jsoftware.com/forums.htm
>
> --
> Met vriendelijke groet,
> @@i = Arie Groeneveld
>
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
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