Introduction (3): Tuples and Unions

2. Union types (definitions) - eg. Options

type Result = Nothing | Value;;

Adding parameter:

type Result = Nothing | Value of float;;
let sqr (x:float) = if x<0 then Nothing else Value (sqrt x);;
sqr -2.0;;

Making type more generic:

type Result<'a> = Nothing | Value of 'a;;    // type 'a Result = ...
sqr 2.0;; // val it: Result<float> = Value 1.414213562

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