[Haskell-beginners] $= operator

I was reading Eleara examples out of Hackage, and I kept noticing lines like this:

t <- get GLFW.time GLFW.time $= 0

Most of the rest of it made more-or-less sense (I mean, there IS a reason I'm still asking questions to beginners!) but I couldn't seem to find anything about it on my usual reference sources, and it's uses don't make that much sense to me.