outcome

Types

ContextStack

A list of context entries

pub type ContextStack =
  List(String)

Outcome

</>

An alias for the Result type. Where the error type is Problem.

pub type Outcome(t, err) =
  Result(t, Problem(err))

Problem

</>

The error type in a result ie. Result(t, Problem(e))

pub type Problem(err) {
  Problem(error: err, stack: List(String))
}

Constructors

Problem(error: err, stack: List(String))

Values

context

</>

pub fn context(
  outcome outcome: Result(t, Problem(err)),
  context context: String,
) -> Result(t, Problem(err))

Add context to a Problem. This will add a context entry to the stack.

Example

Error("Something went wrong")
|> outcome.outcome
|> outcome.context("In find user function")

map_error

</>

pub fn map_error(
  outcome: Result(t, Problem(err)),
  mapper: fn(err) -> err,
) -> Result(t, Problem(err))

Map the error value

new_problem

</>

pub fn new_problem(error: err) -> Problem(err)

Create a Problem Use this if you need the Problem type only. Usually you will use outcome instead.

Example

outcome.new_problem("Something went wrong")

outcome

</>

pub fn outcome(result: Result(t, err)) -> Result(t, Problem(err))

Convert Result(a, e) to Result(a, Problem(e))

Example

Error("Something went wrong")
|> outcome.outcome

pretty_print

</>

pub fn pretty_print(
  problem: Problem(err),
  to_s: fn(err) -> String,
) -> String

Pretty print a Problem, including the stack. The latest problem appears at the top of the stack.

Example

let result = Error("Something went wrong")
|> outcome.outcome
|> outcome.context("In find user function")
|> outcome.context("More context")

case result {
  Error(problem) ->
    outcome.pretty_print(function.identity)

  Ok(_) -> todo
}

Something went wrong

stack:
 In find user function
 More context

print_line

</>

pub fn print_line(
  problem: Problem(err),
  to_s: fn(err) -> String,
) -> String

Print problem in one line

Example

let result = Error("Something went wrong")
|> outcome.outcome
|> outcome.context("In find user function")

case result {
  Error(problem) ->
    outcome.print_line(function.identity)

  Ok(_) -> todo
}

Something went wrong < In find user function

remove_problem

</>

pub fn remove_problem(
  outcome: Result(t, Problem(err)),
) -> Result(t, err)

Remove the Problem wrapping in the error value

Example

let outcome = Error("Fail") |> outcome.outcome

outcome.remove_problem(outcome) == Error("Fail")

with_context

</>

pub fn with_context(
  error_context: String,
  next: fn() -> Result(a, Problem(b)),
) -> Result(a, Problem(b))

Convenient function for adding context at the top of a function that returns an Outcome.

Example

fn do_something(user_id: String) -> Outcome(AnswerType, ErrorType) {
  use <- with_context("user_id " <> user_id)

  ...
}

This is equivalent to adding `|> outcome.context(...)` to each
of the results in the body of the function