gleam/result
Result represents the result of something that may succeed or not.
Ok means it was successful, Error means it was not successful.
Functions
pub fn all(results: List(Result(a, b))) -> Result(List(a), b)Combines a list of results into a single result.
If all elements in the list are Ok then returns an Ok holding the list of values.
If any element is Error then returns the first error.
Examples
> all([Ok(1), Ok(2)])
Ok([1, 2])
> all([Ok(1), Error("e")])
Error("e")
pub fn flatten(result: Result(Result(a, b), b)) -> Result(a, b)Merges a nested Result into a single layer.
Examples
> flatten(Ok(Ok(1)))
Ok(1)
> flatten(Ok(Error("")))
Error("")
> flatten(Error(Nil))
Error(Nil)
pub fn is_error(result: Result(a, b)) -> BoolChecks whether the result is an Error value.
Examples
> is_error(Ok(1))
False
> is_error(Error(Nil))
True
pub fn is_ok(result: Result(a, b)) -> BoolChecks whether the result is an Ok value.
Examples
> is_ok(Ok(1))
True
> is_ok(Error(Nil))
False
pub fn lazy_or(first: Result(a, b), second: fn() -> Result(a, b)) -> Result(
a,
b,
)Returns the first value if it is Ok, otherwise evaluates the given function for a fallback value.
Examples
> lazy_or(Ok(1), fn() { Ok(2) })
Ok(1)
> lazy_or(Ok(1), fn() { Error("Error 2") })
Ok(1)
> lazy_or(Error("Error 1"), fn() { Ok(2) })
Ok(2)
> lazy_or(Error("Error 1"), fn() { Error("Error 2") })
Error("Error 2")
pub fn lazy_unwrap(result: Result(a, b), or default: fn() -> a) -> aExtracts the Ok value from a result, evaluating the default function if the result
is an Error.
Examples
> lazy_unwrap(Ok(1), fn() { 0 })
1
> lazy_unwrap(Error(""), fn() { 0 })
0
pub fn map(over result: Result(a, b), with fun: fn(a) -> c) -> Result(
c,
b,
)Updates a value held within the Ok of a result by calling a given function
on it.
If the result is an Error rather than Ok the function is not called and the
result stays the same.
Examples
> map(over: Ok(1), with: fn(x) { x + 1 })
Ok(2)
> map(over: Error(1), with: fn(x) { x + 1 })
Error(1)
pub fn map_error(over result: Result(a, b), with fun: fn(b) -> c) -> Result(
a,
c,
)Updates a value held within the Error of a result by calling a given function
on it.
If the result is Ok rather than Error the function is not called and the
result stays the same.
Examples
> map_error(over: Error(1), with: fn(x) { x + 1 })
Error(2)
> map_error(over: Ok(1), with: fn(x) { x + 1 })
Ok(1)
pub fn nil_error(result: Result(a, b)) -> Result(a, Nil)Transforms any error into Error(Nil).
Examples
> nil_error(Error(1))
Error(Nil)
> nil_error(Ok(1))
Ok(1)
pub fn or(first: Result(a, b), second: Result(a, b)) -> Result(
a,
b,
)Returns the first value if it is Ok, otherwise returns the second value.
Examples
> or(Ok(1), Ok(2))
Ok(1)
> or(Ok(1), Error("Error 2"))
Ok(1)
> or(Error("Error 1"), Ok(2))
Ok(2)
> or(Error("Error 1"), Error("Error 2"))
Error("Error 2")
pub fn replace(result: Result(a, b), value: c) -> Result(c, b)Replace the value within a result
Examples
> replace(Ok(1), Nil)
Ok(Nil)
> replace(Error(1), Nil)
Error(1)
pub fn replace_error(result: Result(a, b), error: c) -> Result(
a,
c,
)Replace the error within a result
Examples
> replace_error(Error(1), Nil)
Error(Nil)
> replace_error(Ok(1), Nil)
Ok(1)
pub fn then(result: Result(a, b), apply fun: fn(a) ->
Result(c, b)) -> Result(c, b)Updates a value held within the Ok of a result by calling a given function
on it, where the given function also returns a result. The two results are
then merged together into one result.
If the result is an Error rather than Ok the function is not called and the
result stays the same.
This function is the equivalent of calling map followed by flatten, and
it is useful for chaining together multiple functions that may fail.
Examples
> then(Ok(1), fn(x) { Ok(x + 1) })
Ok(2)
> then(Ok(1), fn(x) { Ok(#("a", x)) })
Ok(#("a", 1))
> then(Ok(1), fn(_) { Error("Oh no") })
Error("Oh no")
> then(Error(Nil), fn(x) { Ok(x + 1) })
Error(Nil)
pub fn unwrap(result: Result(a, b), or default: a) -> aExtracts the Ok value from a result, returning a default value if the result
is an Error.
Examples
> unwrap(Ok(1), 0)
1
> unwrap(Error(""), 0)
0
pub fn unwrap_both(result: Result(a, a)) -> aExtracts the inner value from a result. Both the value and error must be of the same type.
Examples
> unwrap_both(Error(1))
1
> unwrap_both(Ok(2))
2
pub fn unwrap_error(result: Result(a, b), or default: b) -> bExtracts the Error value from a result, returning a default value if the result
is an Ok.
Examples
> unwrap_error(Error(1), 0)
1
> unwrap_error(Ok(""), 0)
0