roc/Core.md

Uses for unions:

1. Reduce

reduce : (a, b -> b | Done), b, Array a -> b

Being able to return Done when you're done means you can implement things like find without needing recursion.

Having to return (Continue val) or Done every time would be tedious. This is a simpler API.

2. Additional guarantees

I can define my reducing function as either of these:

reduceFn : String, Int -> Int

reduceFn : String, Int -> Int | Done

These types unify, meaning I can say something more specific about my types than I can with something like Maybe. "This reduce call never bails out early."

Example:

fibonacci : Int -> Int fibonacci = index -> if index <= 1 then index else fibonacci (index - 1) + fibonacci (index - 2)

Array

empty : Array *

isEmpty : Array * -> Bool

length : Array * -> Int

get : Int, Array elem -> elem | Nil

put : Int, elem, Array elem -> Array elem

push : elem, Array elem -> Array elem

concat : Array elem, Array elem -> Array elem

find : (elem -> Bool) -> Array elem -> elem | Nil

map : (a -> b), Array a -> Array b

indexedMap : (Int, a -> b), Array a -> Array b

reduce : (a, b -> b | Done), b, Array a -> b

reduceFromEnd : (a, b -> b | Done), b, Array a -> b

keepIf : (elem -> Bool), Array elem -> Array elem

dropIf : (elem -> Bool), Array elem -> Array elem

String

isEmpty : String -> Bool

length : String -> Int

replace : { every : String, with : String }, String -> String

concat : String, String -> String

join : String, Array String -> String

split : String, String -> Array String

takeFirst : Int, String -> String

takeLast : Int, String -> String

dropFirst : Int, String -> String

dropLast : Int, String -> String

startsWith : String, String -> Bool

endWith : String, String -> Bool

toInt : String -> Int | Nil

toFloat : String -> Float | Nil

fromInt : Int -> String

fromFloat : Float -> String

toUpper : String -> String

toLower : String -> String

trim : String -> String

padStart : Int, String -> String

padEnd : Int, String -> String