Pattern matching with guards vs if/else construct in F#

Question

In ML-family languages, people tend to prefer pattern matching to if/else construct. In F#, using guards within pattern matching could easily replace if/e

Answer 1

Agree with @Daniel that pattern matching is usually more flexible. Check this implementation:

type Solution = | Identity | Roots of float list

let quadraticEquation x =

    let rec removeZeros list =
        match list with
        | 0.0::rest -> removeZeros rest
        | _ -> list
    let x = removeZeros x

    match x with
    | [] -> Identity // zero constant
    | [_] -> Roots [] // non-zero constant
    | [a;b] -> Roots [ -b/a ] // linear equation
    | [a;b;c] ->
        let delta = b*b - 4.0*a*c
        match delta with
        | delta when delta < 0.0 -> 
            Roots [] // no real roots
        | _ ->
            let d = sqrt delta
            let x1 = (-b-d) / (2.0*a)
            let x2 = (-b+d) / (2.0*a)
            Roots [x1; x2]
    | _ -> failwithf "equation is bigger than quadratic: %A" x

Also notice in https://fsharpforfunandprofit.com/learning-fsharp/ that it is discouraged to use if-else. It is considered a bid less functional.