diamond.fsx

open System
// We can not work with radius of the diamond outside 0 to 25
let CreateRadius (i:int) = 
    match i with 
        | i when i = 0 && i < 26 -> Some i
        | _ -> None

let radius = CreateRadius 20 |> Option.get

let axis = [|-radius .. radius|]
type Point = { x : int; y: int;}
type PointWithLetter = { p: Point; c: Char}

let TaxicabNorm p =  
    abs p.x + abs p.y

let indexedLetters =
    ['A' .. 'Z'] |> Seq.mapi (fun i l -> i,l) 

let findLetter (p: Point) =
    let _,l = Seq.find(fun (i, _) -> i = abs p.y) indexedLetters 
    l

let createAllPoints vector = 
    seq { for x in vector do for y in vector do yield {x=x;y=y} }

let allPoints = createAllPoints axis 

let diamond = allPoints 
            |> Seq.filter (fun p -> TaxicabNorm p = radius) 
            |> Seq.map( fun p -> { p=p; c=findLetter p })

// Everything below is just for drawing the diamond
// Returns a 2d point array to draw in
let axisTo2D axis = 
    [| for _ in axis -> (Array.map (fun _ -> '.') axis) |]

let drawing = axisTo2D axis 

let findIndexInAxis elem axis =
    Array.findIndex (fun x -> x = elem) axis

for pointWithChar in diamond do
    let yindex = findIndexInAxis pointWithChar.p.y axis
    let xindex = findIndexInAxis pointWithChar.p.x axis
    drawing.[xindex].[yindex] <- pointWithChar.c

let printArray (arr: char array) = new string (arr) |> sprintf "%A" |> Console.WriteLine 

for line in drawing do
    printArray line