Why List partition works while span does not

Question

I have this List oX of (Char, Int) pars (it contains pairs with only unique Char values)

List(( ,3), (d,1), (e,3), (h,3), (i,1) , (l,3), (o,2), (r,2), (t,1),         


        

Answer 1

From the documentation of span: "Returns the longest prefix of the list whose elements all satisfy the given predicate, and the rest of the list."

So here span gives you the expected result: since the first tuple in your list doesn't have the character d, the longest prefix of the list where each tuple has the character d is indeed the empty list.