[erlang-questions] Maps branch and disclaimers

Chris King <>
Wed Oct 30 15:38:35 CET 2013


On Wed, 30 Oct 2013 10:24:20 -0400, Björn-Egil Dahlberg <>  
wrote:

>
>> BTW, is there a plan for a type notation for these new maps, or for how  
>> to get Dialyzer to usefully >>type-check them?
>
>  Yes. The type notation is the same as with other terms.

Ya, I just found that and posted a separate e-mail with my analysis.  I  
believe the type signatures to be inconsistently specified.


> How well Dialyzer would be able to handle it is a different matter. I  
> plan to make them really stupid at first, >meaning opaque map(). Later  
> incarnations of dialyzer could be increasingly smarter.

I think it will be very difficult for Dialyzer to automatically tease  
apart the homogeneous (list-like) and heterogeneous (tuple-like) use  
cases, even if they are not mixed.  In particular, as I mentioned in my  
other e-mail, the useful type variance in the heterogeneous use case is  
the opposite of the useful type variance in the homogeneous case.  (i.e.,  
we want to know that a heterogeneous map contains *at least* some keys; we  
want to know that a homogeneous map contains *at most* some keys).

Maybe I am wrong – I hope I am – but without a plan and without the  
hetero-homogeneous distinction, I fear "later" could be "never".
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