[plt-dev] Typed Scheme: function type declarations should support optional args

Can't he write a macro that unfolds into a type specification, at  
least for his uses?



On Mar 29, 2010, at 9:44 AM, Sam Tobin-Hochstadt wrote:

> On Mon, Mar 29, 2010 at 9:31 AM, Noel Welsh <noelwelsh at gmail.com>  
> wrote:
>> This common pattern
>>
>> (define (foo a [b 1] [c 2] [d 3]) ...)
>>
>> which expands into a case-lambda like
>>
>> (define foo
>>  (case-lambda (([a] (foo a 1 2 3))
>>                        ([a b] (foo a b 2 3)) ...))
>>
>> is a damn pain to type and Type in Typed Scheme. It would be really
>> nice it one could just write:
>>
>> (: foo (Integer [Integer] [Integer] [Integer] -> Integer))
>> (define (foo a [b 1] [c 2] [d 3]) ...)
>>
>> in Typed Scheme.
>
> Wouldn't it though ...
>
> Really, there are two separate issues here - a convenient syntax for
> types with optional arguments, and support for defining functions with
> optional arguments.  The first is less of a pain, but probably
> something I could implement pretty easily.  Unfortunately, the second
> is significantly harder, because the expansion of such definitions is
> quite convoluted.  As a short-term work-around, you can use
> `opt-lambda' from `mzlib/etc', whose expansion is much simpler.
> -- 
> sam th
> samth at ccs.neu.edu
> _________________________________________________
>  For list-related administrative tasks:
>  http://list.cs.brown.edu/mailman/listinfo/plt-dev