Greetings, I'm struggling to find a way to define an "Alist" once, and then simply add-in "Fields" to it incrementally.. without having to keep using new identifiers/variables to hold the result of each "addin" expression. I understand that pure Functional Programming doesn't use destructive state changes, but I'm wondering if there is a way to make this happen using Monads, for example (which I have a cursory understanding of..) Instead of doing this: type Root = String type Oct = Integer type Mode = Integer data Field = Root Root | Oct Oct | Mode Mode deriving (Show) type Alist = [Field] addin :: Alist -> Field -> Alist addin p f = f:p p0 :: Alist p0 = [] p1 = addin p0 (Root "c") p2 = addin p1 (Oct 4) p3 = addin p2 (Mode 3) p4 = addin p3 (Oct 3) -- ... p42, etc For the Alist version, when adding-in a Field with the same constructor-name as one that has already been added-in, it adds-in a brand new entry (with a repeated key-name (in the form of another constructor) and its associated value), as a normal association list does.. I'm also looking to define a Property-List version, where a Field-name/constructor can update a previous value (if the Field has already been added), or add-in a new entry if the Field hasn't been added yet. Many Thanks, Tom Jordan