outcome

Types

ContextStack

A list of context entries

pub type ContextStack =
  List(String)

Outcome

</>

Alias to Result with Problem as error type.

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

Problem

</>

The error type ie. Result(t, Problem) This contains the error, the severity and the context stack.

pub type Problem(err) {
  Problem(error: err, severity: Severity, stack: ContextStack)
}

Constructors

Problem(error: err, severity: Severity, stack: ContextStack)

Severity

</>

An application error is either a Defect or a Failure. A Defect is an unexpected application error, which shouldn’t be shown to the user. A Failure is an expected error.

pub type Severity {
  Defect
  Failure
}

Constructors

```
Defect
```
```
Failure
```

Functions

context

</>

pub fn context(
  outcome outcome: Result(a, Problem(b)),
  context context: String,
) -> Result(a, Problem(b))

Add context to an Outcome This will add a Context entry to the stack

Example

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

error_with_defect

</>

pub fn error_with_defect(defect: a) -> Result(b, Problem(a))

Create a Defect wrapped in an Error

Example

case something {
  True -> Ok("Yay")
  False -> error_with_defect("Something went wrong")
}

error_with_failure

</>

pub fn error_with_failure(failure: a) -> Result(b, Problem(a))

Create Failure wrapped in an Error

Example

case something {
  True -> Ok("Yay")
  False -> error_with_failure("Invalid input")
}

extract_error

</>

pub fn extract_error(
  outcome: Result(a, Problem(b)),
) -> Result(a, b)

Remove the Problem wrapping, returning just your error.

into_defect

</>

pub fn into_defect(result: Result(a, b)) -> Result(a, Problem(b))

Convert an Error(String) into an Error(Defect) This is useful when you have a Result(t, String) and want to convert it into a Result(t, Problem)

Example

Error("Something went wrong")
|> into_defect

into_failure

</>

pub fn into_failure(
  result: Result(a, b),
) -> Result(a, Problem(b))

Convert an Error(String) into an Error(Failure) This is useful when you have a Result(t, String) and want to convert it into a Result(t, Problem)

Example

Error("Invalid input")
|> into_failure

map_defect

</>

pub fn map_defect(
  outcome: Result(a, Problem(b)),
  mapper: fn(b) -> b,
) -> Result(a, Problem(b))

map_error

</>

pub fn map_error(
  outcome: Result(a, Problem(b)),
  mapper: fn(b) -> b,
) -> Result(a, Problem(b))

Map the error value inside a Problem

map_failure

</>

pub fn map_failure(
  outcome: Result(a, Problem(b)),
  mapper: fn(b) -> b,
) -> Result(a, Problem(b))

map_into_defect

</>

pub fn map_into_defect(
  result: Result(a, b),
  mapper: fn(b) -> c,
) -> Result(a, Problem(c))

Convert an Error(t) into a wrapped Defect, by using a mapping function Similar to into_defect, but takes a function to map the error value to a string

map_into_failure

</>

pub fn map_into_failure(
  result: Result(a, b),
  mapper: fn(b) -> c,
) -> Result(a, Problem(c))

Convert an Error(t) into a wrapped Failure, by using a mapping function Similar to into_defect, but takes a function to map the error value to a string

pretty_print

</>

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

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

Example

Error("Something went wrong")
|> into_defect
|> context("In find user function")
|> context("More context")
|> pretty_print(function.identity)

Defect: Something went wrong

stack:
 More context
 In find user function

print_line

</>

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

Print problem in one line

Example

Error("Something went wrong")
|> into_defect
|> context("In find user function")
|> print_line(function.identity)

Defect: Something went wrong << In find user function

replace_with_defect

</>

pub fn replace_with_defect(
  result: Result(a, b),
  e: c,
) -> Result(a, Problem(c))

Replaces an Error(t) with an Error(Defect)

Example

Error(Nil)
|> replace_with_defect("Something went wrong")

replace_with_failure

</>

pub fn replace_with_failure(
  result: Result(a, b),
  e: c,
) -> Result(a, Problem(c))

Replaces any Error(t) with an Error(Failure)

Example

Error(Nil)
|> replace_with_failure("Invalid input")

tap

</>

pub fn tap(
  outcome: Result(a, Problem(b)),
  fun: fn(Problem(b)) -> c,
) -> Result(a, Problem(b))

Use tap functions to log the errors

tap_defect

</>

pub fn tap_defect(
  outcome: Result(a, Problem(b)),
  fun: fn(b) -> c,
) -> Result(a, Problem(b))

tap_error

</>

pub fn tap_error(
  outcome: Result(a, Problem(b)),
  fun: fn(b) -> c,
) -> Result(a, Problem(b))

tap_failure

</>

pub fn tap_failure(
  outcome: Result(a, Problem(b)),
  fun: fn(b) -> c,
) -> Result(a, Problem(b))

unwrap_failure

</>

pub fn unwrap_failure(problem: Problem(a), default_value: a) -> a

Use this to show a failure to a user. If the Problem is a failure, it will show that otherwise it will show the default message given. We don’t want to show defect messages to users.

Example

case result {
 Ok(value) -> io.debug("Success")
 Error(problem) -> io.error(unwrap_failure(problem, "Something went wrong"))
}