[racket-dev] case-> and for/sum:

On 01/04/2013 01:27 PM, Jens Axel Søgaard wrote:
> 2013/1/3 Neil Toronto <neil.toronto at gmail.com>:
>> I solved it by not using `for/sum' and writing this ridiculous function for
>> the recursive base case and the initial values in `x':
>>
>>    (: zero-of (case-> (Real -> Real)
>>                       (Number -> Number)))
>>    (define (zero-of x) 0)
>>
>> Fortunately, it should get inlined. I also renamed `U' to `V', because it
>> was overshadowing the type name.
>
> Thanks for the solution.
>
> I am very fond of for and friends in Racket code, and
> it annoys me to port these constructs to Typed Racket.
> I know the goal is for Typed Racket to use the
> output of the macro expansion of for and friends,
> but maybe it is worth the effort to implement Typed
> Racket versions of the most used for-variants?

The general goal of using untyped macros in TR code without a hitch is 
difficult because macros tend to introduce indirection (e.g. renaming) 
that throws off local type inference.

FWIW, Vincent and Sam aren't against specialized TR macros. For example, 
the `for/vector:' and `for*/vector:' exported by `typed/racket' are 
written from scratch instead of being wrappers for `for/vector' and 
`for*/vector'.

I gave `for/sum:' a little thought recently, though, and I couldn't 
think of how to make it work without annotations. Maybe you'll have more 
success. I'm less motivated to fix `for/sum:' than you are. :D

Neil ⊥