[Haskell-beginners] what type is 'Val 9' when 'Val Int' a ctor for 'Expr e'?

The attachment compiles OK; yet, I don't understand how the compiler knows what type val_9 has. The compile/run is: <---cut here--- Compilation started at Tue Oct 21 13:17:41 make runghc uniplate.try.hs val_9=Val 9 add_8_9=Add (Val 8) (Val 9) children_add_8_9=[Val 8,Val 9] Compilation finished at Tue Oct 21 13:17:42

---cut here--- I would have expected that I would need to code this:

let val_9 = (Val 9)::(Expr Eo) but apparently not. Could somebody explain? TIA. -Larry