Random expression generator

expressiongen.fsx

open System

// Type which represent simple expression.
type Expr =
| Int32 of int32
| Add of Expr * Expr
| Sub of Expr * Expr
| Mul of Expr * Expr
| Div of Expr * Expr
| Mod of Expr * Expr

let generator fuel = 
    let rec gen fuel =
        if fuel <= 0 then
            let value = Random.Shared.Next(100)
            (Int32 value, value)
        else
            let op = Random.Shared.Next(5)
            let (left, leftValue) = gen (fuel - 1)
            let (right, rightValue) = gen (fuel - 1)
            match (op, rightValue) with
            | (0, _) -> (Add (left, right), leftValue + rightValue)
            | (1, _) -> (Sub (left, right), leftValue - rightValue)
            | (2, _) -> (Mul (left, right), leftValue * rightValue)
            | (3, x) when x <> 0 -> (Div (left, right), leftValue / rightValue)
            | (_, x) when x <> 0 -> (Mod (left, right), leftValue % rightValue)
            | (_, _) -> gen (fuel - 1)
    gen fuel

let (expr, value) = generator 3
printfn "Expression"
printfn "%A" expr
printfn "Value"
printfn "%d" value