I wondered whether there was a conscious link in the minds of early language designers to Church encoding of booleans. (well, other than McCarthy and Lisp)

A Church boolean is either:

  true = λt.λf.t
  false = λt.λf.f

So instead of writing an expression with keywords like

  if bool then yep else nope

Just use the boolean as a function and apply it to the then and else clauses like

  bool yep nope

So the shape is very similar to modern languages, but with less syntactic scaffolding.