A system for represeNtiNg Natural Numbers iNductively usiNg oNly two symbols, "0" (zero) aNd "S" (successor). This could be expressed as a recursive data type with the followiNg Haskell defiNitioN: 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)
