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[ASYNC-38] keep</> instead of map</> Created: 18/Nov/13  Updated: 05/May/14

Status: Open
Project: core.async
Component/s: None
Affects Version/s: None
Fix Version/s: None

Type: Enhancement Priority: Minor
Reporter: Leon Grapenthin Assignee: Unassigned
Resolution: Unresolved Votes: 0
Labels: documentation, enhancement, errormsgs


 Description   

One problem with using map< is when the supplied function returns nil. In such case (using the latest implementation from core.async [org.clojure/core.async "0.1.256.0-1bf8cf-alpha"]) one can take nil from a channel created with map<. This is otherwise only possible with closed channels. Putting nil on a channel normally throws an IllegalArgumentException.

With the current implementation of map< it is not possible to determine whether the source-channel was closed or the supplied function returned nil.

Notice that putting onto a channel created with map> throws an IllegalArgumentException when the supplied function returns nil as if you would put nil onto a channel.

My proposal is to add keep</> (where nil values returned from the supplied function are ignored and nothing is put) to the core library or to implement map</> as keep</> since having a real map</> instead of keep</> hardly makes sense when nil is not permitted anyways.



 Comments   
Comment by Leon Grapenthin [ 24/Apr/14 3:44 AM ]

It is still an issue in "0.1.278.0-76b25b-alpha" that you can only use impl.protocols/closed? to consistently determine whether a channel created with map</> was closed - if nil is one of your predicates return values.

Of course, you could use a predicate that never returns nil. But what should be the benefit of map</> being able to magically pass nil while everything else isn't?

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