Road to Elm - The Strange Case of "<~"

Chances are, if you've been reading Elm code older than a year, that you've seen a strange squiggly symbol <~.

It used to be exposed by the Signal namespace, but was then obsoleted in favour of just using its full name Signal.map (which is now itself obsolete).

in merge (dir <~ Keyboard.arrows) (dir <~ Keyboard.wasd)

becomes

in Signal.merge (Signal.map dir Keyboard.arrows) (Signal.map dir Keyboard.wasd)