[racket] Why Typed Racket is faster?

From: Sam Tobin-Hochstadt (samth at cs.indiana.edu)
Date: Mon Feb 24 09:30:33 EST 2014

On Mon, Feb 24, 2014 at 9:24 AM, Vincent St-Amour <stamourv at ccs.neu.edu> wrote:
>> It took me hours and hours to enumerate all possible ways but still
>> unsolved.
>> (define: random-gaussian : (case-> [[#:mean Flonum] [#:stddev Flonum]
>> [#:multiple False] -> Flonum]
>>                                    [[#:mean Flonum] [#:stddev Flonum]
>> [#:multiple Index] -> (Listof Flonum)])
>>   {lambda {#:mean [μ 0.0] #:stddev [σ 1.0] #:multiple [p #false]}
>>     (define: samples : FlVector (flnormal-sample μ σ (if (false? p) 1 p)))
>>     (cond [(false? p) (flvector-ref samples 0)]
>>           [else (flvector->list samples)])})
>> Actually, DrRacket complains about (Values Flonum)
>> So 'multiple values' is evil!
>> Keyword argument is also the optional one, it's good for stopping (case->)
>> becoming too complexity. But why not (false? p) tells Typed Racket to
>> choose the first function types?
> That's odd. I'll look into it.

This program doesn't actually have the type ascribed -- if you treat
it as having the second type, it should always return a (Listof
Flonum), but when no arguments are passed it returns a single Flonum.

However, the fix, which is to remove the optionality in the #:multiple
argument in the second branch of the case-> type, doesn't cause it to
typecheck. I think the levels of encoding between keyword functions
and the typechecker will make this hard to do, but Asumu has looked
into keyword functions most recently, and my have ideas.


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