Re: let ... in layout

From: Jean-Yves Moyen (Jean-Yves.Moyen@loria.fr)
Date: Wed Mar 15 2000 - 09:22:34 MET

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    On 15 Mar 2000, Julian Assange wrote:

    >
    > let .. in
    > let .. in ...
    >
    > seems such a common construct in caml that it could do with some
    > syntatic sugar. I often see let..in run to 5-20 clauses. This appears
    > incredibly ugly compared to the equivalent haskell code, is harder to
    > read and takes longer to write due to the clutter of the surrounding
    > token magic. Has anyone thought about applying layout in general to
    > ocaml, or otherwise sugaring let...in? Is there any reason why the BNF
    >
    > let {name = expr}+ in
    >
    > would be ambiguous?

    I guess one can write:
    let silly f=
      let x=List.map f z=3 in
        ...

    which can be read either:
    let silly f=
      let x=List.map f in
      let z=3 in
        ...

    or:
    let silly f=
      let x=List.map in
      let f z=3 in
        ...

    Of course, if your definition aren't mutually recursive, you can use 'and'
    to separate two deifferent definitons:
    let x=t
    and y=u
    and ...
    and z=v in
      ...

    which is not so long to write, unambigous and readable (I find).

    > The only other haskell features I frequently miss, are list
    > comprehensions and multiple argument pattern matching.

    I don't understand exactly what you mean by 'multiple argument pattern
    matching', but I guess you could just use a tuple-pattern matching:

    let f a b c=
      match a,b,c with
        ...

    which allows you to match several arguments at once.

    Hypocoristiquement,
    Jym.



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