Hi all, I thought I'd share some of the subtle nuances in designing the strictness properties of the containers API. I currently feel that we lack a good guiding principle in making this decisions. There are several different points along the lazy-to-strict spectrum. For example: # Everything lazy (including the spine) We don't use this. I think it's a bad idea. It can make an insert finish in O(1) just to have a subsequent null check take O(n*log n) time. # Spine strict Quite inefficient as keys aren't unboxed in e.g. lookup and insert. # Strict in keys inserted into the map Also ineffecient as keys still can't be unboxed as there's usually a base case in each loop where the key isn't used. # Strict in key arguments This is what that Lazy API uses. Makes it possible to unbox keys. Good trade-off between performance and expressibility. Means that you can't write: lookup undefined empty which "Strict in keys inserted into the map" would have let you write. # Strict in values inserted into the map Minimum required to avoid space leaks for e.g. a map of Int values that are modified in a loop. # Strict in value arguments This is what the Strict API uses. This allows you to not do any external forcing of values passed to the containers API if you want to make sure they are evaluated. Cheers, Johan