On 07/14/2016 08:07 AM, Christopher Howard wrote:
Hi again all. From some online research, I understand that operations on complex immutable structures (for example, a "setter" function a -> (Int, Int) -> Matrix -> Matrix which alters one element in the Matrix) is not necessarily inefficient in Haskell, because the (compiler? runtime?) has some means of sharing unchanged values between the input and output structure. What I am not clear on, however, is how this works, and how you ensure that this happens. Could someone perhaps elaborate, or point me to a really good read on the subject?
https://en.wikipedia.org/wiki/Persistent_data_structure See in particular the section "Trees". (It basically works the same for records; just imagine that a record is a 2-level tree, where each field/label in the record is an edge from the "field label" to the "field value". Multiple levels of records work essentially work the same as multi-level trees do.)