review

ex1-ex2

tests work

ex3

looks good, there is no explanation to what a block is though.

General

IfThenElse should return a unit type if there is no else statement, also you should typecheck the else block if it exists.

Currently it passes if you put 23 + false in the else.

Check for an optional else block like this

match e { Some(e) => todo!(), None => todo!(), }