Re: Library proposal: add a Location interface for element-wise?operations on Data.Map (#4887)

Chung-chieh Shan wrote:

Ross Paterson wrote:

...

http://code.haskell.org/~ross/containers_doc/Data-Map.html#3

Great!

Given that no function takes two Locations at once, a Location can be thought of (and implemented) as a record whose fields are "key", "before", "after", etc. To support this thought, it would be nice if all functions that take a Location as argument take it as the first argument. That seems already the case except in "assign".

Since the Location comes with invariants (the keys in before must be smaller than the keys in after ), the user may not construct it with record syntax, so it doesn't really matter whether one of the exported functions is composed with flip . However, implementing it as a record could be one way to make it faster, if GHC were to implement some kind of absence analysis. Namely, the idea is that the records fields are independent of each other and usually not used all at once. If GHC could detect this, for instance by using strictness analysis, then only a specialized/fused version of the Path needs to be built. Regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com