[racket-dev] Typed versions of untyped collections

On Dec 17, 2012, at 6:10 PM, Neil Toronto wrote:

>>> 
>>> `plot' is written in untyped Racket. There's no performance problem with typed plots at all; in fact, using `plot/typed' from TR code ends up checking exactly the same contracts for the same plots. `plot/typed' is just another end-user that happens to re-export everything with types attached.
>> 
>> I don't understand this last part at all. You have
>> 
>> -- an untyped file M
>> -- a typed file T that imports M and re-exports everything from there with types
>> 
>> How can it possibly be the case that a client C imports T and does NOT pay for the contracts that T's types impose on the call chain?
> 
> That would only happen if client C is untyped. I wouldn't expect an untyped client to (require plot/typed), but I suppose it could happen.


Wait. This is the line I don't understand: 

C is TYPED. It requires T. 
T is TYPED. It requires M. 
M is UNTYPED. 

If c in C calls t in T, this first call does not add any overhead. OK. 
But t is really m from M obtained with a require/typed. [Alternatively, it is redefinition that calls such a function.]

It is this call from t to m that imposes the overhead. 

Why are you saying that "There's no performance problem with typed plots at all"?