Converting Discriminated Union case to string

Question

I am working on a FAKE project using F# - I am not fluent in F# or functional first programming, and am mostly doing front-end formatting. I am trying to set the color of an item based off of a class variable assigned to it. I am having issues converting this into string or using it in an if statement. I know its a long-shot, but are there any F# developers out there who might have experience in this area?

the class:

type State =
    | New
    | Open
    | Closed
    | Archived

the item to be recolored:

  td [ ClassName "text-center" ] [ statusTag appt.state ]

I am primarily a C# developer, so the way that F# does things is very foreign. Normally i would just create an if statement and plug the state into it with a .ToString(), then use that to restyle but I am stumped as to how to go about it using F#. Any help would be greatly appreciated.

Answer 1

The usual way is to examine your value with a match expression:

let stateToColor state = 
    match state with
    | New -> "red"
    | Open -> "green"
    | Closed -> "blue"
    | Archived -> "yellow"

But of course you can also use an if expression, almost like in C#:

let stateToColor state =
    if state = New then "red"
    elif state = Open then "green"
    elif state = Closed then "blue"
    else "yellow"

The latter is a bit less safe though: if you later add another State and forget to also add it to stateToColor, the compiler will catch you if you use the match expression, but not for if/then/else.