CODEWITHSUNDEEP
haskellcons
Atir
Atir

Reputation: 163

Haskell: What is the meaning of :.?

A symbol combined (:.) of cons following by a dot.

Taken from here:

-- The custom list type
data List t =
  Nil
  | t :. List t
  deriving (Eq, Ord)

-- Right-associative
infixr 5 :.

Taken from here: https://github.com/tonymorris/fp-course

Upvotes: 2

Views: 256

Answers (1)

willeM_ Van Onsem
willeM_ Van Onsem

Reputation: 476594

In short: the code constructs an alterative version of a list, and (:.) is one of the two data constructors.

Well it is a data constructor of the List t data type. For example the standard list [a] has two data constructors [] and (:), here the code introduces a new data constructor (:.), but it acts completely the same way as the "cons" of the standard list (:).

So the code defines it as:

data List t = Nil | (:.) t (List t) deriving (Eq, Ord)

and like any data constructor, we can do pattern matching on it, construct new lists, etc.

Upvotes: 6

Related Questions