Syntax decision

[Brian Goetz]

The need for disambiguation in overload resolution is very important. 
Don't write that off as being of "low" priority.

On 9/28/2011 10:58 AM, Ali Ebrahimi wrote:
> Hi,
> I think with great support for type inference the need for casting
> lambas (unless for disambiguating overloaded methods,... ) would be low.
> And this ambiguity can be solved by applying some precedence in favor of
> lambdas or versa.
>
> Best Regards.
>
> On Wed, Sep 28, 2011 at 6:11 PM, Brian Goetz <brian.goetz at oracle.com
> <mailto:brian.goetz at oracle.com>> wrote:
>
>     The nilary syntax is still a thorn.  But the obvious solution outlined
>     below -- allow elision of the () -- leads to a syntactic ambiguity.  If
>     -> { statement; } were a valid lambda, then is:
>
>        (identifier) -> { statement; }
>
>     a one-arg lambda with inferred type, or a cast of a nilary lambda?
>
>     If people have brilliant other suggestions for nilary lambda syntax,
>     we'd consider it.
>
>
>
>     On 9/28/2011 2:03 AM, Howard Lovatt wrote:
>      > Personally I am glad you have decided to go with -> since I have had
>      > trouble reading Scala code, however this is not my main point in this
>      > post which is have you decided if you require () for no arguments
>     or if
>      > you plan to allow a 'naked' -> e.g.:
>      >
>      > shortCutAnd( -> size >= 0, -> size < max ); // Example equivalent
>      > to size >= 0 && size < max, but user written
>      >
>      > On 28 September 2011 05:18, Brian Goetz <brian.goetz at oracle.com
>     <mailto:brian.goetz at oracle.com>
>      > <mailto:brian.goetz at oracle.com <mailto:brian.goetz at oracle.com>>>
>     wrote:
>      >
>      >     Update on syntax: the EG has chosen to stick with the -> form
>     of the
>      >     arrow that the prototype currently uses, rather than adopt
>     the =>.
>      >
>      >     You could think of this in two ways (I'm sure I'll hear both):
>      >
>      >       - This is much better, as it avoids some really bad
>     interactions with
>      >     existing operators, such as:
>      >
>      >         x => x.age <= 0;                 // duelling arrows
>      >     or
>      >         Predicate p = x => x.size == 0;  // duelling equals
>      >
>      >       - What a bunch of idiots we are, in that we claimed the
>     goal of doing
>      >     what other languages did, and then made gratuitous changes
>     "just for the
>      >     sake of doing something different".
>      >
>      >     Obviously we don't think we're idiots, but everyone can have an
>      >     opinion :)
>      >
>      >     In the end, this was viewed as a small tweak to avoid some
>     undesirable
>      >     interactions, while preserving the overall goal of "mostly
>     looks like
>      >     what lambdas look like in other similar languages."
>      >
>      >
>      >
>      >     On 9/8/2011 4:07 PM, Brian Goetz wrote:
>      > > This just in: the EG has (mostly) made a decision on syntax.
>      > >
>      > > After considering a number of alternatives, we decided to
>     essentially
>      > > adopt the C# syntax.  We may still deliberate further on the fine
>      >     points
>      > > (e.g., thin arrow vs fat arrow, special nilary form, etc), and
>      >     have not
>      > > yet come to a decision on method reference syntax.
>      > >
>      > > The C# syntax is:
>      > >
>      > >     lambda = ArgList Arrow Body
>      > >     ArgList = Identifier
>      > >               | "(" Identifier [ "," Identifier ]* ")"
>      > >               | "(" Type Identifier [ "," Type Identifier ]* ")"
>      > >     Body = Expression
>      > >               | "{" [ Statement ";" ]+ "}"
>      > >
>      > > Here are some examples of lambda expressions using this syntax:
>      > >
>      > >     x =>  x + 1
>      > >     (x) =>  x + 1
>      > >     (int x) =>  x + 1
>      > >     (int x, int y) =>  x + y
>      > >     (x, y) =>  x + y
>      > >     (x, y) =>  { System.out.printf("%d + %d = %d%n", x, y, x+y); }
>      > >     () =>  { System.out.println("I am a Runnable"); }
>      > >
>      > > The decision to choose this syntax was twofold:
>      > >    - The syntax scores "pretty well" on most subjective measures
>      >     (though
>      > > has cases where it looks bad, just like all the others do).  In
>      > > particular, it does well with "small" lambdas that are used as
>     method
>      > > arguments (a common case), and also does well with large
>      > > (multi-statement) lambdas.
>      > >
>      > >    - Despite extensive searching, there was no clear winner
>     among the
>      > > alternatives (each form had some good aspects and some really not
>      >     very
>      > > good aspects, and there was no form that was clearly better
>     than the
>      > > others).  So, we felt that it was better to choose something
>     that has
>      > > already been shown to work well in the two languages that are
>      >     most like
>      > > Java -- C# and Scala -- rather than to invent something new.
>      > >
>      > > A compiler implementation should be available soon.
>      > >
>      > >
>      > >
>      >
>      >
>      >
>      >
>      > --
>      >    -- Howard.
>      >
>
>