Computation Expression

TaskResultOption Computation Expression

Namespace: FsToolkit.ErrorHandling

Examples

Example 1

The TaskResultOption.map2 example can be written using the taskResultOption computation expression as below:

// Task<Result<UserTweet option, exn>>
taskResultOption {
  let! post = getPostById samplePostId
  let! user = getUserById post.UserId
  return userTweet post user
}

Example 2

The taskResultOption CE supports binding from multiple compatible types, allowing you to mix TaskResultOption, TaskResult, Result, Option, Task, and Async values without manual conversion:

// parseMode: string -> Result<Mode, string>
// loadUniverse: Mode -> Task<Result<Universe, string>>

// Task<Result<Report option, string>>
taskResultOption {
  // Bind from Result<Mode, string> directly (no manual conversion needed)
  let! mode = parseMode "fast"

  // Bind from Task<Result<Universe, string>> directly
  let! universe = loadUniverse mode

  return generateReport universe
}

Supported Source Types

The taskResultOption CE supports let! and return! with the following types:

Type	Behavior
Task<Result<'ok option, 'error>>	Identity (the CE's native type)
Task<Result<'ok, 'error>>	Ok value is wrapped in Some
Task<'ok option>	Some/None is wrapped in Ok
Task<'ok>	Value is wrapped in Some and then Ok
Result<'ok, 'error>	Ok value is wrapped in Some, lifted to Task
Choice<'ok, 'error>	Converted to Result, then same as Result
'ok option	Some/None wrapped in Ok, lifted to Task
Async<Result<'ok, 'error>>	Ok value is wrapped in Some
Async<'ok>	Value is wrapped in Some and then Ok