What does the `<<` operator mean in elm?

Question

In the following code taken from Elm Form Example, line 122, what does the << operator mean?

Field.field Field.defaultStyle (Signal.send updat         


        

Answer 1

It is function composition. For your concrete example it means

\x -> (Signal.send updateChan (toUpdate x))

In elm it's not a part of the syntax but part of the standard library: Basics.<<