CODEWITHSUNDEEP
listif-statementf#
wardz
wardz

Reputation: 379

Making my function return an error message

I'm trying to make my function return "invalid Input" when it finds an empty sublist.

let func (lst: 'a list list) =
    if List.contains [] lst then
        printfn "%s" "Invalid Input"
    else
        List.map List.head lst

This is what I've tried but this of course doesn't work since my if/else returns two different types.

Upvotes: 1

Views: 75

Answers (2)

dumetrulo
dumetrulo

Reputation: 1991

You could use a Result type:

let func lst =
    if List.contains [] lst
    then Error "Invalid input"
    else Ok (List.map List.head lst)

Upvotes: 2

aloisdg
aloisdg

Reputation: 23521

I think you should raise an exception. By the way, you may want to use List.isEmpty:

let func (lst: 'a list list) =
    if List.contains [] lst then
        raise (System.ArgumentException("Invalid Input"))
    else
        List.map List.head lst

You can also replace raise with invalidArg "lst"

let func (lst: 'a list list) = 
   if List.isEmpty lst then invalidArg "lst" "Input is empty"
   else List.map List.head lst

Learn more: Exceptions | F# for fun and profit or msdn.

Then you can catch the exception to retrieve the exception.

Upvotes: 1

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