ML records and variant types

These examples show two ways of constructing new types in OCaml: records and variant types.

(* C:\Documents and Settings\Default\Desktop\4651\examples\types.ml *)

(* a record type: specifies components *)

type color = {red: int; green: int; blue: int};;

let yellow = {red = 255; green = 255; blue = 0};;

let inverse c = {red = 255 - c.red; green = 255 - c.green; blue = 255 - c.blue};;

(* a function defined without pattern-matching *)
let isBlue c = if c.blue > 0 then true else false;;

isBlue yellow;;

isBlue (inverse (yellow));;

(* same function with pattern-matching *)
let isBlue = function 
{red=r; green=g; blue=0} -> false 
| _ -> true;;

isBlue yellow;;

isBlue (inverse (yellow));;

(* a variant type: specifies alternatives *)

type 'a list = Empty | Node of 'a * 'a list;;

let emptylist = Empty;;

let mylist = (Node (5, (Node (3, Empty))));;

let isEmpty = function 
 Empty -> true
| _ -> false;;

isEmpty emptylist;;

isEmpty mylist;;

let rec countList = function
  Empty -> 0
| Node( _ , l) -> 1 + countList (l);;

countList Empty;;

countList mylist;;