List notation

We are used to the list notation [0,1,2,3]. However it is syntactic sugar for (0:1:2:3:[]). By using the syntactic sugar, we often miss the benefits of the direct notation.

• A trailing colon is like a terminator.

0 :
1 :
2 :
3 :
[]

Thus it is more theoretically sound and easier to edit.

• You can easily mix elements and lists into a list by appending the corresponding operator in each line:

[1,2,3] ++
4 :
listA ++
5 :
listB ++
[]

• You can construct a singleton list with a section of the colon operator:

  (:[]) :: a -> [a]
  

  .
• You can prepend an element to a list:

  (x:) :: [a] -> [a]
  

  . E.g.

  iterate (' ':) []
  

  creates a list of blank strings with increasing size very efficiently.

See also:

• Haskell-Cafe thread: Comma in the front