List

List is what FP programmers typically use to store a sequence of values because it is friendly to recursion. Array is what most mainstream languages use. Due to JavaScript's strict runtime (as opposed to Haskell's lazy runtime), most PureScript developers will use Array instead of List. However, explaining some FP concepts are easier to do using List rather than Array.

Understand the upcoming definition using this diagram:

    List
   /   \
head   tail
      /  \
   head  tail
           \
           ....
          /  \
       head  Nil
-- Data.List.Types

data List a
  = Nil
  | Cons a (List a)

infixr 6 Cons as :

-- example
1 : 2 : Nil -- Cons 1 (Cons 2 Nil) -- [1, 2]
PackageType name"Plain English" name
purescript-listList aImmutable strict singly-linked list
UsageValues & their Usage
Recursive-friendly, not-best-performant list type
  • Nil - Indicates the end of a List in pattern matching
  • Cons a (List a) - stores one value of the list (head) and the tail, which is either the rest of the list (another Cons) or the end of the list (Nil).