Very cool!

Does it replace identical expressions in the same scope? Like:

    let tau = 3.14 +. 3.14

becomes

    let pi = 3.14
    let tau = pi +. pi

?

EDIT: Or even crazier with function:

    let _ = (x + 1) + (y + 1)

becomes

    let plus_one a = a + 1
    let _ = (plus_one x) + (plus_one y)

(I ask this just out of curiosity. Even the "simpler" version is very impressive!)