Anonymous function syntax

[Timon Gehr]

On 09/25/2011 11:43 AM, Mafi wrote:
> Am 22.09.2011 22:54, schrieb Andrei Alexandrescu:
>> On 9/21/11 5:17 PM, Walter Bright wrote:
>>> I've collected a few from various languages for comparison:
>> [snip]
>>
>> I think we should do the following:
>>
>> 1. Introduce a new token "=>"
>>
>> 2. Add this rewrite to the grammar:
>>
>> symbol => expression
>>
>> translates to
>>
>> (symbol) { return expression; }
>>
>> 3. Add this rewrite to the grammar:
>>
>> symbol1 symbol2 => expression
>>
>> translates to
>>
>> (symbol1 symbol2) { return expression; }
>>
>> 4. Add this rewrite to the grammar:
>>
>> (comma_separated_parms) => expression
>>
>> translates to
>>
>> (comma_separated_parms) => expression
>>
>> Each item in comma_separated_parms may be 1 or 2 symbols separated by
>> whitespace. Example:
>>
>> (int a, b) => a + b
>>
>> is valid and translates to (int a, b) { return a + b; }
>>
>> 5. The expression cannot contain commas at top level; an unparenthesized
>> comma is considered to finish expression, just like in a function call's
>> argument list. For example:
>>
>> fun(int a => a + 1, a + 2)
>>
>> is interpreted as
>>
>> fun((int a => a + 1), (a + 2))
>>
>> To use comma inside expression, add parens around it.
>>
>> 5. Remove bugs and limitations. A function literal may specify none,
>> all, or some parameter types, and the compiler correctly figures out the
>> appropriate template and non-template parameters. The literal
>> subsequently converts to function pointer or delegate whenever there's a
>> match of parameter and result types.
>>
>>
>>
>> Andrei
>
> If we decide to add something like this, the => 'operator' has in my
> opinion to have a higher precidence thand ! or you should be able to
> write it at least without parenthesis (using other parser tricks).
> Like this:
>
> map!x=>x+1(list)
>


It cannot have higher precedence than !, because then your example would 
be parsed as

(map!(x=>x))+(1(list))

Other parser tricks are impossible, because:

map!(x=>x+y(list))

and

map!(x=>x+y)(list)

cannot be distinguished without parens.