[nem-en] Re: match on specific parameter

[Kamil Skalski]

2006/1/29, Michal Moskal <michal.moskal at gmail.com>:
> Some more thoughts:
>
> On 1/29/06, Michal Moskal <michal.moskal at gmail.com> wrote:
> > But I personally don't find it very readable. I would like something
> > like:
> >
> > def rev (acc, match lst)
> >   | x :: xs => rev (x :: acc, xs)
> >   | [] => acc

I like this one. It should be allowed on any subset of parameters:

def rev  (match lst, acc)
  | x :: xs => rev (x :: acc, xs)
  | [] => acc

Then the standard
def foo (x, y) {
  | (1, 2) => ...
}

would be a shortcut for
def foo (match x, match y) {
  | (1, 2) => ...
}

The problem of single / multiple matching bothers be for a long time.
Ocaml allows to
"implicitly" match on one or more LAST parameters, maybe this is not
as bad design as I thought some time ago.

> >
> > or maybe "def rev (acc, match)". I'm not sure about the syntax.
>
> Maybe we could use default parameters as a hint:
>
> def rev (lst, acc = [])
>    | x :: xs => ...

It is not even clear what it means... Is it equivalent to:
def rev (lst, acc)
  (x :: xs, []) =>


or to the original example
def rev (lst, acc)
  match (lst)
     | x :: xs =>

?

> >
> > On a related note, d proposed on IRC, that we could transform:
> >
> > foo () : ...
> >   | ...
> >
> > inside classes and variants to:
> >
> > foo () : ...
> >   match (this)
> >     | ...
> >
> > which I think also makes sense.

Nice, but I think it is a little bit "unclean". That is, 'this' comes
there from nowhere. Also, would you ommit this rule if there is some
parameter?

>
> Maybe it should be also possible to say:
>
> foo (match this, some_flag : bool)
>   | ...
>

I guess
foo (some_flag : bool)
  match (this)
    |

is cleaner.


--
Kamil Skalski
http://nazgul.omega.pl