jarlestabell

type Expr = Number of int | Plus of Expr * int | Minus of Expr * int

let rec eval = function 
  | Number n -> n
  | Plus(e, n) -> (eval e) + n
  | Minus(e, n) -> (eval e) - n

let rec exprAsString = function 
  | Number n -> n.ToString()
  | Plus(e, n) -> sprintf "%s + %d" (exprAsString e) n

jarlestabell

let calcExpr n =
  let rec innerCalcExpr n current last=
    if current>last then "" else  [|""; "+"; "-"|].[n%3] + string current + innerCalcExpr (n/3) (current+1) last
  "1" + innerCalcExpr n 2 9

let rec sum = function
  |(op::h::t) -> (int (op+h)) + sum t
  | _ -> 0
  
let eval text =   sum ("+" :: (System.Text.RegularExpressions.Regex.Split(text,@"(\+)|(-)") |> List.ofArray))

jarlestabell

let calcExpr digitCount n=
  let rec innerCalc n current=
    if current>digitCount then "" else [|" - "; ""; " + "|].[n%3] + string current + innerCalc (n/3) (current+1)
  "1" + innerCalc n 2

let eval digitCount n=
  let rec innerCalc n current (partialsum, partialnumber)=
    if current>digitCount then partialsum + partialnumber
    else
      let nextPartials = if n % 3 = 1 then (partialsum, partialnumber * 10 + (current * (sign partialnumber)))