~$ racket
  Welcome to Racket v7.2.0.6.
  > (define True (lambda (t f) (t)))
  > (define False (lambda (t f) (f)))
  > (define If (lambda (b tr fa) (b tr fa)))
  > (define P (lambda (x)
                (If x
                    (lambda () (display "It was true!"))
                    (lambda () (display "It was false!")))))
  > (P True)
  It was true!
  > (P False)
  It was false!
  > 

To learn about the lambda calculus, check out chapter 5 of "Types and Programming Languages", Benjamin C. Pierce, MIT Press 2002. You might also get something out of "Semantics Engineering with PLT Redex", Felleisen, Findler & Flatt, MIT Press 2009.