life

life.fsx

// q: how would you encode Conways rule of life in f#?
// a: how about a pattern match emitting an action?

type Action = NoChange | BecomeInactive | BecomeActive
/// return what should happen to the central cell given active neighbor count
let kernel' centralCell activeNeighbors =
    match centralCell, (activeNeighbors<2), (activeNeighbors>3), activeNeighbors=3 with
    | true,true,_,_ -> BecomeInactive      // living cell with fewer than two neighbors dies
    | true,false,false,_ -> NoChange       // living cell with two or three neighbors lives to next generation
    | true,false,true,_ -> BecomeInactive  // living cell with more than there neighbors dies
    | false,_,_,true -> BecomeActive       // empty cell with exactly three neighbors births new life 
    | false,_,_,false -> NoChange

Cool.

Could you also implement it like so?

match isCentralCellActive, activeNeighbors = 2, activeNeighbors = 3
true, false, false -> BecomeInactive
false, _, true -> BecomeActive
_, _, _ -> NoChange

It's not as explicit with the rules, but it seems easier to understand.