Result
Result ok err : [ Ok ok, Err err ]
The result of an operation that could fail: either the operation went okay, or else there was an error of some sort.
isOk : Result ok err -> Bool
Return Bool.true if the result indicates a success, else return Bool.false
Result.isOk (Ok 5)
isErr : Result ok err -> Bool
Return Bool.true if the result indicates a failure, else return Bool.false
Result.isErr (Err "uh oh")
withDefault : Result ok err, ok -> ok
If the result is Ok, return the value it holds. Otherwise, return
the given default value.
Result.withDefault (Ok 7) 42 Result.withDefault (Err "uh oh") 42
map : Result a err, (a -> b) -> Result b err
If the result is Ok, transform the value it holds by running a conversion
function on it. Then return a new Ok holding the transformed value. If the
result is Err, this has no effect. Use mapErr to transform an Err.
Result.map (Ok 12) Num.negate Result.map (Err "yipes!") Num.negate
Functions like map are common in Roc; see for example List.map,
Set.map, and Dict.map.
mapErr : Result ok a, (a -> b) -> Result ok b
If the result is Err, transform the value it holds by running a conversion
function on it. Then return a new Err holding the transformed value. If
the result is Ok, this has no effect. Use map to transform an Ok.
Result.mapErr (Err "yipes!") Str.isEmpty Result.mapErr (Ok 12) Str.isEmpty
try : Result a err, (a -> Result b err) -> Result b err
If the result is Ok, transform the entire result by running a conversion
function on the value the Ok holds. Then return that new result. If the
result is Err, this has no effect. Use onErr to transform an Err.
Result.try (Ok -1) \num -> if num < 0 then Err "negative!" else Ok -num Result.try (Err "yipes!") \num -> if num < 0 then Err "negative!" else Ok -num
onErr : Result a err, (err -> Result a otherErr) -> Result a otherErr
If the result is Err, transform the entire result by running a conversion
function on the value the Err holds. Then return that new result. If the
result is Ok, this has no effect. Use try to transform an Ok.
Result.onErr (Ok 10) \errorNum -> Str.toNat errorNum Result.onErr (Err "42") \errorNum -> Str.toNat errorNum