function types syntax

[Rémi Forax]

Le 05/01/2010 14:36, Peter Levart a écrit :
> Strawman proposal specifies the following syntax for function types (without throws declaration for now, but it suggests that it could be added later):
>
> # Type ( TypeList opt ) ThrowsDecl opt
>
> For example:
>
> #void() - a function taking no arguments returning nothing
> #BigDecimal(String) throws ParseException - a function taking a single String returning BigDecimal throwing ParseException
> ##int(int)(#int(int)) - function taking a single (function taking a single int returning int) returning a function taking a single int returning int
>
> I'm wondering if the leading '#' is necessary. Would it be ambiguous to leave it out?

I think there is a problem with the cast and parenthesis between 
expression :
   (A())
can be read as a cast to a function that returns a A or as a call to 
function A
between parenthesis.


> The above examples would then read:
>
> void()
> BigDecimal(String) throws ParseException
> int(int)(int(int))
>
> I think someone mentioned that similarity between the syntax-es of function types and lambda expressions is actually not a good thing.
>    

someone = me

But I prefer use # for function type and introduce a contextual keyword 
named lambda for lambda expressions
lambda(int x) (x)  instead of  #(int x) (x)

lambda is a contextual keyword because it can be used anywhere as a 
variable name or as a type
without a compile time error. So there is no source backward 
compatibility problem.

The only problem with this approach is that you can't use () to call a 
function type,
you have to use something like .invoke()

#void(int) f = ...
f.invoke(3);   // instead of f(3);

And frankly try to write a lambda that takes a function type is not 
humanly readable
with the syntax of the strawman proposal:
#(#int() f) (f())

This is a little better with the keyword lambda:
lambda(#int() f) (f.invoke())

It also better fit with current reflection API because it doesn't 
require change.

> What do you think?
>
> Regards, Peter
>
>    

regards,
Rémi