Module: list/indexing

Methods

(static) elemIndex(n, xs) → {Maybe}

Return the index of the first value of a List equal to a query value, or Nothing if there is no such value.
Haskell> elemIndex :: Eq a => a -> [a] -> Maybe Int

Parameters:
Name Type Description
n *

The query value
xs List

The List to evaluate
Source:
Returns:

Just n or Nothing

Type
Maybe
Example
const lst = list(1,2,2,3,2,4,2,2,5,2,6,8);
elemIndex(8, lst);                         // => Just 11
elemIndex(10, lst);                        // => Nothing

(static) elemIndices(n, xs) → {List}

Return the indices of all values in a List equal to a query value, in ascending order.
Haskell> elemIndices :: Eq a => a -> [a] -> [Int]

Parameters:
Name Type Description
n *

The query value
xs List

The List to evaluate
Source:
Returns:

A List of values equal to n

Type
List
Example
const lst = list(1,2,2,3,2,4,2,2,5,2,6,8);
elemIndices(2, lst);                       // => [1:2:4:6:7:9:[]]
elemIndices(10, lst);                      // => [[]]

(static) find(p, xs) → {Maybe}

Take a predicate function and a List and return the first value in the list that satisfies the predicate, or Nothing if there is no such element. This function currently only works on List objects, but should in the future work for all Foldable types.
Haskell> find :: Foldable t => (a -> Bool) -> t a -> Maybe a

Parameters:
Name Type Description
p function

The predicate function
xs List

The List to evaluate
Source:
Returns:

The value inside a Just or Nothing, otherwise

Type
Maybe
Example
const lst = list(1,2,3,4,5,6,7,8,9,10);
const pred1 = x => x % 3 === 0;
const pred2 = x => x > 10;
find(pred1, lst);                       // => Just 3
find(pred2, lst);                       // => Nothing

(static) findIndex(p, xs) → {Maybe}

Take a predicate function and a List and return the index of the first value in the list that satisfies the predicate, or Nothing if there is no such element.
Haskell> findIndex :: (a -> Bool) -> [a] -> Maybe Int

Parameters:
Name Type Description
p function

The predicate function
xs List

The List to evaluate
Source:
Returns:

The index inside a Just or Nothing, otherwise

Type
Maybe
Example
const lst = list(1,2,3,4,5,6,7,8,9,10);
const pred1 = x => x % 3 === 0;
const pred2 = x => x > 10;
findIndex(pred1, lst);                  // => Just 2
findIndex(pred2, lst);                  // => Nothing

(static) findIndices(p, xs) → {List}

Return the indices of all values in a List that satisfy a given predicate function, in ascending order.
Haskell> findIndices :: (a -> Bool) -> [a] -> [Int]

Parameters:
Name Type Description
p function

The predicate function
xs List

The List to evaluate
Source:
Returns:

The List of matching indices

Type
List
Example
const lst = list(1,2,3,4,5,6,7,8,9,10);
const pred = x => even(x);
findIndices(pred, lst);                 // => [1:3:5:7:9:[]]

(static) index(as, n) → {*}

Return the value from a List at the specified index, starting at 0.
Haskell> (!!) :: [a] -> Int -> a

Parameters:
Name Type Description
as List

The List to index into
n number

The index to return
Source:
Returns:

The value at the specified index

Type
*
Example
const lst = list(1,2,3,4,5);
index(lst, 3));              // => 4