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by wrbs 1367 days ago
There's nothing about the lambda calculus which forces you to use the church encoding of natural numbers.

You could also come up with an encoding based on booleans as bits:

  {true} = \t f. t
  {false} = \t f. f
then bytes:

  {0b00001111} = \f. f [false] [false] [false] [false] [true] [true] [true] [true]
which you could merge up into larger integers just like real computers.

or for one less based on the 8-bits and to keep the infinite range you could just represent integers as lists of binary numbers:

  {[]} = \c n. n
  {x::y} = \c n. c x y

  {0} = []
  {1} = [true]
  {2} = [false, true] (i.e. reversed 0b10)
  {3} = [true, true]
  {4} = [false, false, true]
which you could imagine using to implement a way more efficient shift-and-add multiply, O(log M * log N)
2 comments

> {[]} = \c n. n

> {x::y} = \c n. c x y

Note that Binary Lambda Calculus uses the simpler {x::y} = \c. c x y, which allows you to operate on a list l with

    l (\head \tail \dummy. non_null_case) null_case
Yeah I made huge assumptions!