Question

I have a C# method that looks a bit like this:

bool Eval() {
  // do some work
  if (conditionA) {
     // do some work
     if (conditionB) {
       // do some work
       if (conditionC) {
         // do some work
         return true;
       }
     }
  }
  return false;
}

In F# this ends up looking quite a bit uglier because of the mandatory else branches:

let eval() =
  // do some work
  if conditionA then
    // do some work
    if conditionB then
      // do some work
      if conditionC then
        // do some work
        true
      else
        false
    else
      false
  else
    false

What would be a cleaner way of writing this in F#?

Answer 1

Well, since ‘do some work’ is already imperative (presumably), then I think that

let eval() =
    let mutable result = false
    ... // ifs
        result <- true
    ... // no more elses
    result

is shorter and reasonable. (In other words, else is only mandatory for if expressions that return values; since you’re doing imperative work, use if statements that don’t need an else.)