Re: [Caml-list] Having '<<', why to use '|>' ?

["Nicolas Pouillard" <nicolas.pouillard@gmail.com>]

Excerpts from Aaron Bohannon's message of Thu Sep 20 16:39:36 +0200 2007:
> It's too bad that $ is reserved for Camlp4.  It would be a natural
> choice for infix application since that's what Haskell uses.

The  old  and  deprecated  `&' operator do perfectly the job. Indeed the OCaml
`&'  operator have the associativity and a precedence close to the Haskell `$'
than what can do the OCaml `$'.

For some more information: http://caml.inria.fr/mantis/view.php?id=2415

> I have used the following notations for function composition in the past:
> 
> let ( |> ) f g x = g (f x)
> let ( <| ) f g x = f (g x)
> 
> I am glad that those are natural to other people, too.  I also like to
> be able to compose predicate functions.  Does anyone have better ideas
> than what is below?
> 
> let ( &&& ) p q x = p x && q x
> let ( ||| ) p q x = p x || q x
> let ( !!! ) p x = not (p x)
> 
> One can also define "%" to do Python-esque string construction,
> although using it with more than one argument requires a nice operator
> for infix application.
> 
> let ( % ) f x = Format.sprintf f x
> 
> "(%c, %n, %s, %b)" % 'a' @@ 12 @@ "hello" @@ true
> 
> "@@" isn't looking so nice to me here.
> 
> And an operator that is very useful (almost essential) in certain
> situations is a monadic "bind" in the list monad:
> 
> let ( >>@ ) xs f = List.flatten (List.map f xs)
> 
> I chose "@" as a reference to the list concatenation operator.
> 
> Are there any others?  Are there better ideas or warnings about the
> ones I have here?
> 
> -Aaron
> 
> > ---------- Forwarded message ----------
> > From: Fabrice Marchant <fabrice.marchant@orange.fr>
> > To: caml-list@yquem.inria.fr
> > Date: Tue, 18 Sep 2007 16:12:46 +0200
> > Subject: Re: [Caml-list] Having '<<', why to use '|>' ?
> >   Thanks Julien !
> >
> > > Have a look at this:
> > >       http://caml.inria.fr/pub/docs/manual-ocaml/lex.html#infix-symbol
> > > With the keywords below.
> > "Note that the following identifiers are keywords of the Camlp4 extensions and should be avoided for compatibility reasons.
> >
> >     parser    <<    <:    >>    $     $$    $:
> > "
> > So no doubt, I'll edit my old programs and replace "<<".
> >
> > > > ... a composition operator ... ( <<< ) ?
> > > > What else ?
> >
> > > I would personally double the '@':
> > >       let (@@) f g x = f @ g x
> >
> >  ( or f (g x) : it is practically the same thing. )
> >
> > A 3 chars operator (<<<) doesn't look smart. Simpler is better.
> > However, about (@@), I preferred to see the direction of the asymmetric composition operator.
> > ( <| ) instead of ( << ) ? Is this a possible idea ?
> >
> >   But maybe your idea is good. Maths use a kind of small 'o' : (f o g) (x) = f (g (x)).
> > It's symmetric like (@@), and that doesn't raise any problem.
> >
> > Cheers,
> >
> > Fabrice
> 

-- 
Nicolas Pouillard aka Ertai