Brent, thanks for answering. Sorry, by "set" I meant "access" [the field "attributes"]. But you already answered, it depends on the ML module implementation choice. One more question about elegance: How to make Examples "sortable" by distance to a reference point "referenceEx"? For instance, if referenceEx was not needed: ----------------------------- listExs = [Example {att=[2,5,3]}, Example {att=[0,2,3]}, Example {att=[2,0,9]}] sortedExamples = sort listExs ================== With referenceEx, I tried this, but it is getting ugly: ------------------------------ sortedExamples = sort $ map (ExamplesPair referenceEx) listExs ================ ------ML.hs------------------------------------------ data ExamplesPairClass = ExamplesPair {ex1 :: Example, ex2 :: Example} deriving (Show, Eq) instance Ord ExamplesPairClass where (ExamplesPair ex1 referenceEx) ≤ (ExamplesPair ex2 referenceEx) = (ex1 distance referenceEx) ≤ (ex2 distance referenceEx) ================================== Sorry that amount of code, it is terrible to read with no colorizing. Davi