F# lightweight syntax for Ocaml with camlp4 - possible?

F# lightweight syntax for Ocaml with camlp4 - possible?

[Dmitry Bely]

Some times ago F# team has introduced a new Caml syntax option called
"lightweight".   From the F# manual:

http://research.microsoft.com/fsharp/manual/lexyacc.aspx
[...]
F# supports the optional use of lightweight syntax through the use of
whitespace to make indentation significant. At the time of this
release this is an experimental feature, though it is assumed that its
use will become widespread. The indentation-aware syntax option is a
conservative extension of the explicit language syntax, in the sense
that it simply lets you leave out certain tokens such as in and ;; by
having the parser take indentation into account. This can make a
surprising difference to the readability of code.
[...]
Basic rules by example

// Without the light syntax option
// 'done' is required
let FunctionSample() =
    let tick x = printf "tick %d\n" x in
    let tock x = printf "tock %d\n" x in
    let choose f g h x =
        if f x then g x else h x in
    for i = 0 to 10 do
        choose (fun n -> n%2 = 0) tick tock i
    done;
    printf "done!\n"

// When the light syntax option is
// enabled 'done' is optional and the scope of
// structured constructs such as match, for, while
// and if/then/else is determined by indentation.
#light
let FunctionSample() =
    let tick x = printf "tick %d\n" x
    let tock x = printf "tock %d\n" x
    let choose f g h x =
        if f x then g x else h x
    for i = 0 to 10 do
         choose (fun n -> n%2 = 0) tick tock i
    printf "done!\n"

[end of quote]

Could the same idea be implemented for Ocaml with Camlp4? Can it use
an indentation level while parsing?

I realize that the third syntax will be 'too much' but it really seems
to be quite useful...

- Dmitry Bely

Re: [Caml-list] F# lightweight syntax for Ocaml with camlp4 - possible?

[Chris King]

On 5/7/07, Dmitry Bely <dmitry.bely@gmail.com> wrote:
> Could the same idea be implemented for Ocaml with Camlp4? Can it use
> an indentation level while parsing?

It has been... http://people.csail.mit.edu/mikelin/ocaml+twt/
But it doesn't use camlp4 (since camlp4 can't modify the lexer to
handle tabs specially).

- Chris

Re: [Caml-list] F# lightweight syntax for Ocaml with camlp4 - possible?

[Nicolas Pouillard]

On 5/8/07, Chris King <colanderman@gmail.com> wrote:
> On 5/7/07, Dmitry Bely <dmitry.bely@gmail.com> wrote:
> > Could the same idea be implemented for Ocaml with Camlp4? Can it use
> > an indentation level while parsing?
>
> It has been... http://people.csail.mit.edu/mikelin/ocaml+twt/
> But it doesn't use camlp4 (since camlp4 can't modify the lexer to
> handle tabs specially).

This is somewhat different in the new version of Camlp4 even if one
cannot dynamically extend the default lexer.

1/ One can now change a Camlp4 module by another, since the
implementation is functorized.

2/ The default lexer now keeps all bits of the input including layout
information.

3/ One can setup a custom token filter, that can handle the
indentation, and then drop the layout information (The default filter
drops layout information).

Best regards,

-- 
Nicolas Pouillard

Re: [Caml-list] F# lightweight syntax for Ocaml with camlp4 - possible?

[Daniel Bünzli]

Le 8 mai 07 à 00:26, Dmitry Bely a écrit :

> I realize that the third syntax will be 'too much' but it really  
> seems to be quite useful...

In a language where you don't enclose function arguments in parens I  
think this is really a bad idea, it makes the code more confusing  
than readable, especially if you try to code with a line width of 80  
columns.

Daniel

Re: [Caml-list] F# lightweight syntax for Ocaml with camlp4 - possible?

[Jon Harrop]

On Tuesday 08 May 2007 00:43, Daniel Bünzli wrote:
> In a language where you don't enclose function arguments in parens I
> think this is really a bad idea, it makes the code more confusing
> than readable, especially if you try to code with a line width of 80
> columns.

As a hardcore OCamler, I must say that I had thought the #light syntax in F# 
to be morally repugnant. However, now that I've forced myself to actually use 
it, I'm finding it to be very useful indeed.

Perhaps the single most important reason why the #light syntax is useful stems 
from the way the F# Visual Studio add-in allows you to execute lines or 
blocks of code in a running interactive session. I'd love to see something 
similar for OCaml but, until then, I don't think the #light syntax would have 
quite the bite for OCaml that it does for F#.

-- 
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
The F#.NET Journal
http://www.ffconsultancy.com/products/fsharp_journal/?e

Re: [Caml-list] F# lightweight syntax for Ocaml with camlp4 - possible?

[skaller]

On Tue, 2007-05-08 at 02:28 +0100, Jon Harrop wrote:

> As a hardcore OCamler, I must say that I had thought the #light syntax in F# 
> to be morally repugnant.

	Haskell = Caml with horizontal humps ..

-- 
John Skaller <skaller at users dot sf dot net>
Felix, successor to C++: http://felix.sf.net