bind

Namespace: FsToolkit.ErrorHandling

Function Signature

('input -> Task<'output voption>) -> Task<'input voption> -> Task<'output voption>

Examples

Take the following function for example

type Account =
  { EmailAddress : string
    Name : string }

// string -> Task<Account voption>
let lookupAccountByEmail email = task {
  let john = { EmailAddress = "[e-mail]"; Name = "John Johnson" }
  let jeff = { EmailAddress = "[e-mail]"; Name = "Jeff Jefferson" }
  let jack = { EmailAddress = "[e-mail]"; Name = "Jack Jackson" }
  
  // Just a map lookup, but imagine we look up an account in our database
  let accounts = Map.ofList [
      ("[e-mail]", john)
      ("[e-mail]", jeff)
      ("[e-mail]", jack)
  ]
  
  return 
    accounts
    |> Map.tryFind email
    |> Option.toValueOption
}

Example 1

let taskOpt : Task<Account voption> =
    TaskValueOption.valueSome "[e-mail]" // Task<string voption>
    |> TaskValueOption.bind lookupAccountByEmail // Task<Account voption>

// task { ValueSome { EmailAddress = "[e-mail]"; Name = "John Johnson" } }

Example 2

let taskVOpt : Task<Account voption> =
    TaskValueOption.some "[e-mail]" // Task<string voption>
    |> TaskValueOption.bind lookupAccountByEmail // Task<Account voption>

// task { ValueNone }

Example 3

let taskVOpt : Task<Account voption> =
    Task.singleton ValueNone // Task<string voption>
    |> TaskValueOption.bind lookupAccountByEmail // Task<Account voption>

// task { ValueNone }