inductively using only two symbols, "0" (zero) and "S"
(successor).
This could be expressed as a
recursive data type with the
data Peano = Zero | Succ Peano
The number three, usually written "SSS0", would be Succ (Succ
(Succ Zero)). Addition of Peano numbers can be expressed as a
simple syntactic transformation:
plus Zero n = n
plus (Succ m) n = Succ (plus m n)
(1995-03-28)