CODEWITHSUNDEEP
f#
Александр Сысоев
Александр Сысоев

Reputation: 1197

Unexpected symbol '<-' in binding

I am a F# newbie. What is wrong with this code?

let setCategory (terminal: MerchantTerminal)
    terminal.Category <- Nullable(MerchantTerminalCategory.NotSet)
    ()

Compiler telling me "Unexpected symbol '<-' in binding. Expected '=' or other token"

MerchantTerminal is C# type:

public class MerchantTerminal
{
    public MerchantTerminalCategory? Category { get; set; }    
}

MerchantTerminalCategory is C# enum

public enum MerchantTerminalCategory
{
    NotSet = 0,
    //other values
}

Upvotes: 2

Views: 608

Answers (2)

Terrance
Terrance

Reputation: 11872

A rough Fsharp Equivalent to your C# code:

type MerchantTerminalCategory = NotSet=0 | Set=1

type MerchantTerminal() =  
    let mutable category = 
        new System.Nullable<MerchantTerminalCategory>()
    member this.Category 
        with get() = category
        and set(value) = category <- value

Usage per your question:

Your usage would look something like this. You were only missing the assignment = op here.

let setCategory (terminal: MerchantTerminal) = //you were missing the assignment "=" op here
    terminal.Category <- Nullable(MerchantTerminalCategory.NotSet)
    ()

Additional comment

As a friendly "code comment" suggestion, one of the benefits of using a construct like that of an enum is to avoid the use of null. If at all possible you should pull out the nullable part and leverage the available states of the enum to represent a default "NotSet" state possibly leveraging what you already have available or via a new state.

Upvotes: 1

Fyodor Soikin
Fyodor Soikin

Reputation: 80744

You're missing an equal sign in your let definition. It needs to be right before the body, like let x = 5 or let f x = x + 5.

Like this:

let setCategory (terminal: MerchantTerminal) =
    terminal.Category <- Nullable(MerchantTerminalCategory.NotSet)
    ()

Upvotes: 4

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