A list that is known, at compile-time, to be nonempty. This means
tail are guaranteed to succeed and you don't have to carry Maybes throughout your program.
import List.Nonempty exposing (..) one = fromElement 2 two = 4 ::: one toList two == [4, 2] head two == 4 tail two ==  toList (reverse two) == [2, 4] toList (dropTail two) ==  member 4 two == True foldl1 (+) two == 6
For actual usage, I recommend
import List.Nonempty as NE exposing (Nonempty, (:::)) to import the type and infix cons.
elm reactor in the test directory, open
Test.elm, and wait a few seconds while libraries are downloaded. Thanks to all the work that went into property-based testing, even if it's overkill for this tiny library.