Fold

Simple, extensible Folds.

Basics

type Fold a b

Uses an input a to accumulate over b.

wrap : (c -> a) -> Fold a b -> Fold c b

Apply a transformation to input of a Fold.

custom : (b -> a -> b) -> Fold a b

Construct a Fold that uses a to accumulate over b.

merge : Fold a b -> b -> a -> b

Evaluate your fold for a given accumulator and input.

list : Fold a (List a)

Cons an element onto the list.

string : Fold Char String

Cons a character onto the string.

arrayLeft : Fold a b -> Fold (Array a) b

Starting from the left, fold each element of the array onto 'b'.

arrayRight : Fold a b -> Fold (Array a) b

Starting from the right, fold each element of the array onto b.

listLeft : Fold a b -> Fold (List a) b

Starting from the left, fold each element of the list onto b.

listRight : Fold a b -> Fold (List a) b

Starting from the right, fold each element of the list onto 'b'.

maybe : Fold a b -> Fold (Maybe a) b

If the input is Just, fold over it.

merge (maybe list) [ 2, 3 ] (Just 1) -- [ 1, 2, 3, 4 ]

merge (maybe string) "hello" Nothing -- "hello"

result : Fold a b -> Fold (Result e a) b

Fold a onto b if Result e a is Ok.

resultError : Fold e b -> Fold (Result e b) b

Fold 'e' onto 'b' if Result e a is Err.

stringLeft : Fold Char b -> Fold String b

Starting from the left, fold each character in the string onto b.

stringRight : Fold Char b -> Fold String b

Starting from the right, fold each character in the string onto b.

passed : Filter a -> Fold a b -> Fold a b

Apply a fold only if the filter passes.

failed : Filter a -> Fold a b -> Fold a b

Apply a fold only if the filter fails.