Keywords that introduce blocks bind more tightly than function application. So f let x is the same as f (let x) and f if b then p else q is the same as f (if b then p else q).
Block keywords bind more tightly than delayed computations syntax. So 'let x'' is the same as _ -> let x and !if b then p else q is the same as (if b then p else q) ().
Blocks eagerly consume expressions, so if b then p else q + r is the same as if b then p else (q + r).