### inits examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of `inits`, which returns all initial segments of a list, shortest first.

```haskell
>>> **inits "abc"
**["","a","ab","abc"]
```

```haskell
>>> **inits []
**[[]]
```

--------------------------------

### inits1 examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of `inits1`, which returns all non-empty initial segments as `NonEmpty` lists.

```haskell
>>> **inits1 "abc"
**['a' :| "",'a' :| "b",'a' :| "bc"]
```

```haskell
>>> **inits1 []
**[]
```

--------------------------------

### iterate examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of iterate with different functions. The last example shows that iterate id is equivalent to repeat.

```haskell
>>> **take 10 $ iterate not True
**[True,False,True,False,True,False,True,False,True,False]
```

```haskell
>>> **take 10 $ iterate (+3) 42
**[42,45,48,51,54,57,60,63,66,69]
```

```haskell
>>> **take 10 $ iterate id 1
**[1,1,1,1,1,1,1,1,1,1]
```

--------------------------------

### subsequences basic example

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Example of subsequences returning all subsequences of a string.

```haskell
>>> subsequences "abc"
["","a","b","ab","c","ac","bc","abc"]
```

--------------------------------

### product examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples for product, which computes the product of numbers in a structure. It hangs on infinite lists.

```haskell
>>> **product []
**1
```

```haskell
>>> **product [42]
**42
```

```haskell
>>> **product [1..10]
**3628800
```

```haskell
>>> **product [4.1, 2.0, 1.7]
**13.939999999999998
```

```haskell
>>> **product [1..]
*** Hangs forever *
```

--------------------------------

### concat examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples for concat, which concatenates all elements of a container of lists.

```haskell
>>> **concat (Just [1, 2, 3])
**[1,2,3]
```

```haskell
>>> **concat (Left 42)
**[]
```

```haskell
>>> **concat [[1, 2, 3], [4, 5], [6], []]
**[1,2,3,4,5,6]
```

--------------------------------

### unzip3 examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of the unzip3 function, which splits a list of triples into three lists.

```haskell
>>> **unzip3 []
**([],[],[])
```

```haskell
>>> **unzip3 [(1, 'a', True), (2, 'b', False)]
**([1,2],"ab",[True,False])
```

--------------------------------

### unzip examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of the unzip function from Data.List, showing the result for an empty list and a list of pairs.

```haskell
>>> **unzip []
**([],[])
```

```haskell
>>> **unzip [(1, 'a'), (2, 'b')]
**([1,2],"ab")
```

--------------------------------

### take examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of take with various inputs, including negative and zero counts, showing the prefix behavior.

```haskell
>>> **take 5 "Hello World!"
**"Hello"
```

```haskell
>>> **take 3 [1,2,3,4,5]
**[1,2,3]
```

```haskell
>>> **take 3 [1,2]
**[1,2]
```

```haskell
>>> **take 3 []
**[]
```

```haskell
>>> **take (-1) [1,2]
**[]
```

```haskell
>>> **take 0 [1,2]
**[]
```

--------------------------------

### repeat examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of repeat: creates an infinite list with the same value. The second example shows that forcing repeat undefined raises an exception.

```haskell
>>> **take 10 $ repeat 17
**[17,17,17,17,17,17,17,17,17, 17]
```

```haskell
>>> **repeat undefined
**[*** Exception: Prelude.undefined
```

--------------------------------

### cycle examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of cycle: ties a finite list into a circular one. Empty list raises an exception; the last example shows laziness.

```haskell
>>> **cycle []
***** Exception: Prelude.cycle: empty list
```

```haskell
>>> **take 10 (cycle [42])
**[42,42,42,42,42,42,42,42,42,42]
```

```haskell
>>> **take 10 (cycle [2, 5, 7])
**[2,5,7,2,5,7,2,5,7,2]
```

```haskell
>>> **take 1 (cycle (42 : undefined))
**[42]
```

--------------------------------

### elemIndices examples: all matching indices

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of `elemIndices` returning all indices of the query element in ascending order.

```haskell
>>> **elemIndices 'o' "Hello World"
**[4,7]
```

```haskell
>>> **elemIndices 1 [1, 2, 3, 1, 2, 3]
**[0,3]
```

--------------------------------

### init examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples for the init function: returning all elements except the last, including a singleton list and an empty list that raises an exception.

```haskell
>>> **init [1, 2, 3]
**[1,2]
```

```haskell
>>> **init [1]
**[]
```

```haskell
>>> **init []
***** Exception: Prelude.init: empty list
```

--------------------------------

### tails examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of `tails`, which returns all final segments of a list, longest first.

```haskell
>>> **tails "abc"
**["abc","bc","c",""]
```

```haskell
>>> **tails [1, 2, 3]
**[[1,2,3],[2,3],[3],[]]
```

```haskell
>>> **tails []
**[[]]
```

--------------------------------

### insert examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of insert, which inserts an element into a sorted list at the first position where it is less than or equal to the next element.

```haskell
>>> **insert (-1) [1, 2, 3]
**[-1,1,2,3]
```

```haskell
>>> **insert 'd' "abcefg"
**"abcdefg"
```

```haskell
>>> **insert 4 [1, 2, 3, 5, 6, 7]
**[1,2,3,4,5,6,7]
```

--------------------------------

### all examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples for all, which determines whether all elements satisfy the predicate. It can return False on an infinite list if a counterexample is found, but hangs if all elements satisfy it.

```haskell
>>> **all (> 3) []
**True
```

```haskell
>>> **all (> 3) [1,2]
**False
```

```haskell
>>> **all (> 3) [1,2,3,4,5]
**False
```

```haskell
>>> **all (> 3) [1..]
**False
```

```haskell
>>> **all (> 3) [4..]
*** Hangs forever *
```

--------------------------------

### singleton examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples for the singleton function: constructing a list from a single element, including a list and a character.

```haskell
>>> **singleton True
**[True]
```

```haskell
>>> **singleton [1, 2, 3]
**[[1,2,3]]
```

```haskell
>>> **singleton 'c'
**"c"
```

--------------------------------

### scanr1 examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of scanr1 with different operators and edge cases. The last example shows that forcing an infinite list with scanr1 causes a stack overflow.

```haskell
>>> **scanr1 (+) [1..4]
**[10,9,7,4]
```

```haskell
>>> **scanr1 (+) []
**[]
```

```haskell
>>> **scanr1 (-) [1..4]
**[-2,3,-1,4]
```

```haskell
>>> **scanr1 (&&) [True, False, True, True]
**[False,False,True,True]
```

```haskell
>>> **scanr1 (||) [True, True, False, False]
**[True,True,False,False]
```

```haskell
>>> **force $ scanr1 (+) [1..]
***** Exception: stack overflow
```

--------------------------------

### splitAt examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of splitAt with various indices, including negative and zero, showing the tuple of prefix and suffix.

```haskell
>>> **splitAt 6 "Hello World!"
**("Hello ","World!")
```

```haskell
>>> **splitAt 3 [1,2,3,4,5]
**([1,2,3],[4,5])
```

```haskell
>>> **splitAt 1 [1,2,3]
**([1],[2,3])
```

```haskell
>>> **splitAt 3 [1,2,3]
**([1,2,3],[])
```

```haskell
>>> **splitAt 4 [1,2,3]
**([1,2,3],[])
```

```haskell
>>> **splitAt 0 [1,2,3]
**([],[1,2,3])
```

```haskell
>>> **splitAt (-1) [1,2,3]
**([],[1,2,3])
```

--------------------------------

### replicate examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of replicate: creates a list of length n with the same value. Negative n yields an empty list.

```haskell
>>> **replicate 0 True
**[]
```

```haskell
>>> **replicate (-1) True
**[]
```

```haskell
>>> **replicate 4 True
**[True,True,True,True]
```

--------------------------------

### partition examples: vowels, even, and less-than

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of `partition` with different predicates: vowel membership, even numbers, and less-than comparison. Each returns a pair of lists.

```haskell
>>> **partition (`elem` "aeiou") "Hello World!"
**("eoo","Hll Wrld!")
```

```haskell
>>> **partition even [1..10]
**([2,4,6,8,10],[1,3,5,7,9])
```

```haskell
>>> **partition (< 5) [1..10]
**([1,2,3,4],[5,6,7,8,9,10])
```

--------------------------------

### map usage examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of map with different functions: adding 1, identity, and a lambda expression. The identity example illustrates that map id == id.

```haskell
>>> map (+1) [1, 2, 3]
[2,3,4]
```

```haskell
>>> map id [1, 2, 3]
[1,2,3]
```

```haskell
>>> map (\n -> 3 * n + 1) [1, 2, 3]
[4,7,10]
```

--------------------------------

### reverse usage examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of reverse on finite and infinite lists. The last example shows that reverse on an infinite list hangs forever because the list must be finite.

```haskell
>>> reverse []
[]
```

```haskell
>>> reverse [42]
[42]
```

```haskell
>>> reverse [2,5,7]
[7,5,2]
```

```haskell
>>> reverse [1..]
* Hangs forever *
```

--------------------------------

### group examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of `group`, which groups consecutive equal elements into sublists. The result is a list of lists.

```haskell
>>> **group "Mississippi"
**["M","i","ss","i","ss","i","pp","i"]
```

```haskell
>>> **group [1, 1, 1, 2, 2, 3, 4, 5, 5]
**[[1,1,1],[2,2],[3],[4],[5,5]]
```

--------------------------------

### any examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples for any, which determines whether any element satisfies the predicate. It can return True on an infinite list if a match is found, but hangs if no match exists.

```haskell
>>> **any (> 3) []
**False
```

```haskell
>>> **any (> 3) [1,2]
**False
```

```haskell
>>> **any (> 3) [1,2,3,4,5]
**True
```

```haskell
>>> **any (> 3) [1..]
**True
```

```haskell
>>> **any (> 3) [0, -1..]
*** Hangs forever *
```

--------------------------------

### transpose basic example

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Basic example of transpose transposing rows and columns of a rectangular list.

```haskell
>>> transpose [[1,2,3],[4,5,6]]
[[1,4],[2,5],[3,6]]
```

--------------------------------

### scanl usage examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of scanl with various functions and inputs, including an infinite list and a case where undefined is not forced.

```haskell
>>> scanl (+) 0 [1..4]
[0,1,3,6,10]
```

```haskell
>>> scanl (+) 42 []
[42]
```

```haskell
>>> scanl (-) 100 [1..4]
[100,99,97,94,90]
```

```haskell
>>> scanl (\reversedString nextChar -> nextChar : reversedString) "foo" ['a', 'b', 'c', 'd']
["foo","afoo","bafoo","cbafoo","dcbafoo"]
```

```haskell
>>> take 10 (scanl (+) 0 [1..])
[0,1,3,6,10,15,21,28,36,45]
```

```haskell
>>> take 1 (scanl undefined 'a' undefined)
"a"
```

--------------------------------

### drop examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of drop with various inputs, including negative and zero counts, showing the suffix behavior.

```haskell
>>> **drop 6 "Hello World!"
**"World!"
```

```haskell
>>> **drop 3 [1,2,3,4,5]
**[4,5]
```

```haskell
>>> **drop 3 [1,2]
**[]
```

```haskell
>>> **drop 3 []
**[]
```

```haskell
>>> **drop (-1) [1,2]
**[1,2]
```

```haskell
>>> **drop 0 [1,2]
**[1,2]
```

--------------------------------

### sum examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples for sum, which computes the sum of numbers in a structure. It hangs on infinite lists.

```haskell
>>> **sum []
**0
```

```haskell
>>> **sum [42]
**42
```

```haskell
>>> **sum [1..10]
**55
```

```haskell
>>> **sum [4.1, 2.0, 1.7]
**7.8
```

```haskell
>>> **sum [1..]
*** Hangs forever *
```

--------------------------------

### lines examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of the lines function, showing how it splits strings on newline characters, including edge cases for empty input and trailing newlines.

```haskell
>>> **lines ""           -- empty input contains no lines
**[]
```

```haskell
>>> **lines "\n"         -- single empty line
**[""]
```

```haskell
>>> **lines "one"        -- single unterminated line
**["one"]
```

```haskell
>>> **lines "one\n"      -- single non-empty line
**["one"]
```

```haskell
>>> **lines "one\n\n"    -- second line is empty
**["one",""]
```

```haskell
>>> **lines "one\ntwo"   -- second line is unterminated
**["one","two"]
```

```haskell
>>> **lines "one\ntwo\n" -- two non-empty lines
**["one","two"]
```

--------------------------------

### foldl1 logical OR example

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Example of foldl1 with logical OR, yielding True.

```haskell
>>> **foldl1 (||) [False, False, True, True]
**True
```

--------------------------------

### foldl1 logical AND example

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Example of foldl1 with logical AND, yielding False.

```haskell
>>> **foldl1 (&&) [True, False, True, True]
**False
```

--------------------------------

### concatMap examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples for concatMap, which maps a function over a container and concatenates the resulting lists.

```haskell
>>> **concatMap (take 3) [[1..], [10..], [100..], [1000..]]
**[1,2,3,10,11,12,100,101,102,1000,1001,1002]
```

```haskell
>>> **concatMap (take 3) (Just [1..])
**[1,2,3]
```

--------------------------------

### unwords examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of the unwords function, which joins strings with spaces, including handling of empty strings.

```haskell
>>> **unwords ["Lorem", "ipsum", "dolor"]
**"Lorem ipsum dolor"
```

```haskell
>>> **unwords ["foo", "bar", "", "baz"]
**"foo bar  baz"
```

--------------------------------

### unionBy examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of unionBy, the non-overloaded version of union. Both arguments may be infinite.

```haskell
>>> **unionBy (>) [3, 4, 5] [1, 2, 3, 4, 5, 6]
**[3,4,5,4,5,6]
```

```haskell
>>> **import Data.Semigroup (Arg(..))
**>>> **unionBy (/=) [Arg () "Saul"] [Arg () "Kim"]
**[Arg () "Saul", Arg () "Kim"]
```

--------------------------------

### words examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of the words function, which splits a string on whitespace and trims leading/trailing spaces.

```haskell
>>> **words "Lorem ipsum\ndolor"
**["Lorem","ipsum","dolor"]
```

```haskell
>>> **words " foo bar "
**["foo","bar"]
```

--------------------------------

### tail examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples for the tail function: returning the elements after the head, including a singleton list and an empty list that raises an exception.

```haskell
>>> **tail [1, 2, 3]
**[2,3]
```

```haskell
>>> **tail [1]
**[]
```

```haskell
>>> **tail []
***** Exception: Prelude.tail: empty list
```

--------------------------------

### stripPrefix examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of `stripPrefix`, which drops a prefix from a list and returns `Just` the remainder or `Nothing` if the prefix does not match.

```haskell
>>> **stripPrefix "foo" "foobar"
**Just "bar"
```

```haskell
>>> **stripPrefix "foo" "foo"
**Just ""
```

```haskell
>>> **stripPrefix "foo" "barfoo"
**Nothing
```

```haskell
>>> **stripPrefix "foo" "barfoobaz"
**Nothing
```

--------------------------------

### break examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of the `break` function, which splits a list at the first element satisfying the predicate. The output is shown for each input.

```haskell
>>> **break (> 3) [1,2,3,4,1,2,3,4]
**([1,2,3],[4,1,2,3,4])
```

```haskell
>>> **break (< 9) [1,2,3]
**([],[1,2,3])
```

```haskell
>>> **break (> 9) [1,2,3]
**([1,2,3],[])
```

--------------------------------

### unsnoc examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples for the unsnoc function: decomposing a list into its init and last, returning Nothing for an empty list.

```haskell
>>> **unsnoc []
**Nothing
```

```haskell
>>> **unsnoc [1]
**Just ([],1)
```

```haskell
>>> **unsnoc [1, 2, 3]
**Just ([1,2],3)
```

--------------------------------

### takeWhile examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of takeWhile with different predicates, showing the longest prefix satisfying the predicate.

```haskell
>>> **takeWhile (< 3) [1,2,3,4,1,2,3,4]
**[1,2]
```

```haskell
>>> **takeWhile (< 9) [1,2,3]
**[1,2,3]
```

```haskell
>>> **takeWhile (< 0) [1,2,3]
**[]
```

--------------------------------

### lookup examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of lookup, which looks up a key in an association list. Returns Nothing if the key is not found; the list must be finite for a Nothing result.

```haskell
>>> **lookup 2 []
**Nothing
```

```haskell
>>> **lookup 2 [(1, "first")]
**Nothing
```

```haskell
>>> **lookup 2 [(1, "first"), (2, "second"), (3, "third")]
**Just "second"
```

--------------------------------

### unsnoc laziness examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Laziness examples for unsnoc: showing how it behaves with undefined elements and partial lists.

```haskell
>>> **fst <$> unsnoc [undefined]
**Just []
```

```haskell
>>> **head . fst <$> unsnoc (1 : undefined)
**Just *** Exception: Prelude.undefined
```

```haskell
>>> **head . fst <$> unsnoc (1 : 2 : undefined)
**Just 1
```

--------------------------------

### null basic examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Basic usage examples for the null function: testing whether a structure is empty.

```haskell
>>> **null []
**True
```

```haskell
>>> **null [1]
**False
```

--------------------------------

### scanl1 usage examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of scanl1 with various functions, including an empty list, infinite list, and a case where undefined is not forced.

```haskell
>>> scanl1 (+) [1..4]
[1,3,6,10]
```

```haskell
>>> scanl1 (+) []
[]
```

```haskell
>>> scanl1 (-) [1..4]
[1,-1,-4,-8]
```

```haskell
>>> scanl1 (&&) [True, False, True, True]
[True,False,False,False]
```

```haskell
>>> scanl1 (||) [False, False, True, True]
[False,False,True,True]
```

```haskell
>>> take 10 (scanl1 (+) [1..])
[1,3,6,10,15,21,28,36,45,55]
```

```haskell
>>> take 1 (scanl1 undefined ('a' : undefined))
"a"
```

--------------------------------

### head examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples for the head function: extracting the first element of a list, including an infinite list and an empty list that raises an exception.

```haskell
>>> **head [1, 2, 3]
**1
```

```haskell
>>> **head [1..]
**1
```

```haskell
>>> **head []
***** Exception: Prelude.head: empty list
```

--------------------------------

### findIndices examples: all matching indices

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of `findIndices` returning all indices of elements satisfying the predicate in ascending order.

```haskell
>>> **findIndices (`elem` "aeiou") "Hello World!"
**[1,4,7]
```

```haskell
>>> **findIndices (\l -> length l > 3) ["a", "bcde", "fgh", "ijklmnop"]
**[1,3]
```

--------------------------------

### minimumBy example with length comparison

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Example of `minimumBy` finding the least element by length. The result is `"!"` because it has the smallest length.

```haskell
>>> **minimumBy (compare `on` length) ["Hello", "World", "!", "Longest", "bar"]
**"!"
```

--------------------------------

### uncons examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples for the uncons function: decomposing a list into its head and tail, returning Nothing for an empty list.

```haskell
>>> **uncons []
**Nothing
```

```haskell
>>> **uncons [1]
**Just (1,[])
```

```haskell
>>> **uncons [1, 2, 3]
**Just (1,[2,3])
```

--------------------------------

### permutations usage examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of permutations for a string, a list of numbers, and the empty list. The order is not lexicographic.

```haskell
>>> permutations "abc"
["abc","bac","cba","bca","cab","acb"]
```

```haskell
>>> permutations [1, 2]
[[1,2],[2,1]]
```

```haskell
>>> permutations []
[[]]
```

--------------------------------

### and examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples for and, which returns the conjunction of a container of Bools. It returns False if a False occurs finitely far from the left, but hangs on an infinite list of True.

```haskell
>>> **and []
**True
```

```haskell
>>> **and [True]
**True
```

```haskell
>>> **and [False]
**False
```

```haskell
>>> **and [True, True, False]
**False
```

```haskell
>>> **and (False : repeat True) -- Infinite list [False,True,True,True,...
**False
```

```haskell
>>> **and (repeat True)
*** Hangs forever *
```

--------------------------------

### !? examples: total list indexing

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of the total list index operator `!?`. Returns `Just` for valid indices and `Nothing` for out-of-bounds or negative indices.

```haskell
>>> **['a', 'b', 'c'] !? 0
**Just 'a'
```

```haskell
>>> **['a', 'b', 'c'] !? 2
**Just 'c'
```

```haskell
>>> **['a', 'b', 'c'] !? 3
**Nothing
```

```haskell
>>> **['a', 'b', 'c'] !? (-1)
**Nothing
```

--------------------------------

### foldl lazy accumulator example

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Shows that foldl reverses the input before prepending to the accumulator, so corecursion starts only after traversing the entire input.

```haskell
>>> **foldl (\acc c -> c : acc) "abcd" "efgh"
**"hgfeabcd"
```

--------------------------------

### foldr1 examples with various inputs

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples for foldr1, a variant of foldr without a base case. It raises a runtime exception on empty structures and hangs on infinite lists.

```haskell
>>> **foldr1 (+) [1..4]
**10
```

```haskell
>>> **foldr1 (+) []
**Exception: Prelude.foldr1: empty list
```

```haskell
>>> **foldr1 (+) Nothing
***** Exception: foldr1: empty structure
```

```haskell
>>> **foldr1 (-) [1..4]
**-2
```

```haskell
>>> **foldr1 (&&) [True, False, True, True]
**False
```

```haskell
>>> **foldr1 (||) [False, False, True, True]
**True
```

```haskell
>>> **foldr1 (+) [1..]
*** Hangs forever *
```

--------------------------------

### tails laziness examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Laziness examples for `tails`, showing that the first element of the result is produced lazily and that the tail can be evaluated without forcing the head.

```haskell
>>> **tails undefined
**[*** Exception: Prelude.undefined
```

```haskell
>>> **drop 1 (tails [undefined, 1, 2])
**[[1, 2], [2], []]
```

--------------------------------

### null infinite structure example

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Example showing that null is expected to terminate even for infinite structures, returning False for an infinite list.

```haskell
>>> **null [1..]
**False
```

--------------------------------

### tails1 laziness examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Laziness examples for `tails1`, showing that the first element is produced lazily and that the tail can be evaluated without forcing the head.

```haskell
>>> **tails1 undefined
***** Exception: Prelude.undefined
```

```haskell
>>> **drop 1 (tails1 [undefined, 1, 2])
**[1 :| [2],2 :| []]
```

--------------------------------

### last examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples for the last function: extracting the last element of a finite list, an infinite list that hangs, and an empty list that raises an exception.

```haskell
>>> **last [1, 2, 3]
**3
```

```haskell
>>> **last [1..]
*** Hangs forever *
```

```haskell
>>> **last []
***** Exception: Prelude.last: empty list
```

--------------------------------

### !! examples: partial list indexing with exceptions

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of the partial list index operator `!!`. Valid indices return the element; out-of-bounds and negative indices raise exceptions.

```haskell
>>> **['a', 'b', 'c'] !! 0
**'a'
```

```haskell
>>> **['a', 'b', 'c'] !! 2
**'c'
```

```haskell
>>> **['a', 'b', 'c'] !! 3
***** Exception: Prelude.!!: index too large
```

```haskell
>>> **['a', 'b', 'c'] !! (-1)
***** Exception: Prelude.!!: negative index
```

--------------------------------

### sortOn examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of using sortOn with a projection function. The first sorts a list of tuples by their first element, the second sorts a list of strings by their length.

```haskell
>>> **sortOn fst [(2, "world"), (4, "!"), (1, "Hello")]
**[(1,"Hello"),(2,"world"),(4,"!")]
```

```haskell
>>> **sortOn length ["jim", "creed", "pam", "michael", "dwight", "kevin"]
**["jim","pam","creed","kevin","dwight","michael"]
```

--------------------------------

### or examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples for or, which returns the disjunction of a container of Bools. It returns True if a True occurs finitely far from the left, but hangs on an infinite list of False.

```haskell
>>> **or []
**False
```

```haskell
>>> **or [True]
**True
```

```haskell
>>> **or [False]
**False
```

```haskell
>>> **or [True, True, False]
**True
```

```haskell
>>> **or (True : repeat False) -- Infinite list [True,False,False,False,...
**True
```

```haskell
>>> **or (repeat False)
*** Hangs forever *
```

--------------------------------

### intercalate usage examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of intercalate inserting a list between lists and concatenating the result. The last example shows that empty inner lists still produce the separator between them.

```haskell
>>> intercalate ", " ["Lorem", "ipsum", "dolor"]
"Lorem, ipsum, dolor"
```

```haskell
>>> intercalate [0, 1] [[2, 3], [4, 5, 6], []]
[2,3,0,1,4,5,6,0,1]
```

```haskell
>>> intercalate [1, 2, 3] [[], []]
[1,2,3]
```

--------------------------------

### filter examples: odd, length, and inequality predicates

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of `filter` with different predicates: odd numbers, string length, and inequality. Each shows the filtered list.

```haskell
>>> **filter odd [1, 2, 3]
**[1,3]
```

```haskell
>>> **filter (\l -> length l > 3) ["Hello", ", ", "World", "!"]
**["Hello","World"]
```

```haskell
>>> **filter (/= 3) [1, 2, 3, 4, 3, 2, 1]
**[1,2,4,2,1]
```

--------------------------------

### notElem examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of notElem, the negation of elem. For infinite structures, it terminates if the value exists at a finite distance from the left side; otherwise it hangs.

```haskell
>>> **3 `notElem` []
**True
```

```haskell
>>> **3 `notElem` [1,2]
**True
```

```haskell
>>> **3 `notElem` [1,2,3,4,5]
**False
```

```haskell
>>> **3 `notElem` [1..]
**False
```

```haskell
>>> **3 `notElem` ([4..] ++ [3])
*** Hangs forever *
```

--------------------------------

### foldl1 subtraction example

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Example of foldl1 with subtraction, yielding -8.

```haskell
>>> **foldl1 (-) [1..4]
**-8
```

--------------------------------

### unlines example

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Example of the unlines function, which appends a newline to each string and concatenates them.

```haskell
>>> **unlines ["Hello", "World", "!"]
**"Hello\nWorld\n!\n"
```

--------------------------------

### dropWhileEnd examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of dropWhileEnd with isSpace and a numeric predicate, showing the suffix dropped.

```haskell
>>> **dropWhileEnd isSpace "foo\n"
**"foo"
```

```haskell
>>> **dropWhileEnd isSpace "foo bar"
**"foo bar"
>>> **dropWhileEnd (> 10) [1..20]
**[1,2,3,4,5,6,7,8,9,10]
```

--------------------------------

### inits1 :: [a] -> [NonEmpty a]

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

The inits1 function returns all non-empty initial segments of a list, shortest first.

```APIDOC
## inits1 :: [a] -> [NonEmpty a]

### Description
The `inits1` function returns all non-empty initial segments of the argument, shortest first.

### Signature
```haskell
inits1 :: [a] -> [NonEmpty a]
```

### Laziness
Note that `inits1` has the following strictness property: `inits1 (xs ++ _|_) = inits1 xs ++ _|_`
In particular, `inits1 _|_ = _|_`

### Examples
```haskell
>>> inits1 "abc"
['a' :| "",'a' :| "b",'a' :| "bc"]

>>> inits1 []
[]
```

`inits1` is productive on infinite lists:
```haskell
>>> take 3 $ inits1 [1..]
[1 :| [],1 :| [2],1 :| [2,3]]
```

_Since: base-4.21.0.0_
```

--------------------------------

### nubBy examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of nubBy, which removes duplicate elements using a user-supplied equality predicate.

```haskell
>>> **nubBy (\x y -> mod x 3 == mod y 3) [1,2,4,5,6]
**[1,2,6]
```

```haskell
>>> **nubBy (/=) [2, 7, 1, 8, 2, 8, 1, 8, 2, 8]
**[2,2,2]
```

```haskell
>>> **nubBy (>) [1, 2, 3, 2, 1, 5, 4, 5, 3, 2]
**[1,2,3,5,5]
```

--------------------------------

### unlines . lines example

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Example showing that unlines . lines is not the identity function when the input is not newline-terminated.

```haskell
>>> **unlines . lines $ "foo\nbar"
**"foo\nbar\n"
```

--------------------------------

### inits :: [a] -> [[a]]

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

The inits function returns all initial segments of a list, shortest first.

```APIDOC
## inits :: [a] -> [[a]]

### Description
The `inits` function returns all initial segments of the argument, shortest first.
`inits` is semantically equivalent to ``map` `reverse` . `scanl` (`flip` (:)) []`, but under the hood uses a queue to amortize costs of `reverse`.

### Signature
```haskell
inits :: [a] -> [[a]]
```

### Laziness
Note that `inits` has the following strictness property: `inits (xs ++ _|_) = inits xs ++ _|_`
In particular, `inits _|_ = [] : _|_`

### Examples
```haskell
>>> inits "abc"
["","a","ab","abc"]

>>> inits []
[[]]
```

`inits` is productive on infinite lists:
```haskell
>>> take 5 $ inits [1..]
[[],[1],[1,2],[1,2,3],[1,2,3,4]]
```
```

--------------------------------

### find examples: matching and non-matching predicates

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples for the `find` function from Data.List. The first returns `Just 45` when the predicate matches an element; the second returns `Nothing` when no element satisfies the predicate.

```haskell
>>> **find (> 42) [0, 5..]
**Just 45
```

```haskell
>>> **find (> 12) [1..7]
**Nothing
```

--------------------------------

### minimum examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Shows the behavior of minimum on a non-empty list, an empty list, and Nothing. The empty cases raise runtime exceptions.

```haskell
>>> minimum [1..10]
1
```

```haskell
>>> minimum []
*** Exception: Prelude.minimum: empty list
```

```haskell
>>> minimum Nothing
*** Exception: minimum: empty structure
```

--------------------------------

### deleteBy examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of deleteBy, which removes the first occurrence of an element using a user-supplied equality predicate.

```haskell
>>> **deleteBy (<=) 4 [1..10]
**[1,2,3,5,6,7,8,9,10]
```

```haskell
>>> **deleteBy (/=) 5 [5, 5, 4, 3, 5, 2]
**[5,5,3,5,2]
```

--------------------------------

### subsequences on infinite input

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Example showing that subsequences is productive on infinite inputs.

```haskell
>>> take 8 $ subsequences ['a'..]
["","a","b","ab","c","ac","bc","abc"]
```

--------------------------------

### unwords and words inverse examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples showing that unwords is neither left nor right inverse of words.

```haskell
>>> **words (unwords [" "])
**[]
>>> **unwords (words "foo\nbar")
**"foo bar"
```

--------------------------------

### dropWhile examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of dropWhile with different predicates, showing the suffix after the longest prefix satisfying the predicate.

```haskell
>>> **dropWhile (< 3) [1,2,3,4,5,1,2,3]
**[3,4,5,1,2,3]
```

```haskell
>>> **dropWhile (< 9) [1,2,3]
**[]
```

```haskell
>>> **dropWhile (< 0) [1,2,3]
**[1,2,3]
```

--------------------------------

### singleton :: a -> [a]

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Construct a list from a single element.

```APIDOC
## singleton :: a -> [a]

### Description
Construct a list from a single element.

### Signature
singleton :: a -> [a]

### Parameters
- **element** (a) - Required - The element to put in the list.

### Return Value
- **[a]** - A list containing the single element.

### Examples
```
>>> singleton True
[True]
>>> singleton [1, 2, 3]
[[1,2,3]]
>>> singleton 'c'
"c"
```
```

--------------------------------

### intersperse usage examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of intersperse inserting an element between the elements of a list, for both character and numeric lists.

```haskell
>>> intersperse ',' "abcde"
"a,b,c,d,e"
```

```haskell
>>> intersperse 1 [3, 4, 5]
[3,1,4,1,5]
```

--------------------------------

### Show [a] instance

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Provides string representation of lists. Available when the element type is an instance of Show.

```APIDOC
## Show [a] instance

### Description
Provides string representation of lists. Available when the element type is an instance of Show.

### Methods
- **showsPrec :: Int -> [a] -> ShowS** - Converts a list to a show function with precedence.
- **show :: [a] -> String** - Converts a list to a string.
- **showList :: [[a]] -> ShowS** - Converts a list of lists to a show function.
```

--------------------------------

### isPrefixOf examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Examples of isPrefixOf, which checks if the first list is a prefix of the second. The first list must be finite for a True result; any mismatch yields False. Infinite first lists cause the function to hang, except when the first list is empty, which returns True immediately.

```haskell
>>> **"Hello" `isPrefixOf` "Hello World!"
**True
```

```haskell
>>> **"Hello" `isPrefixOf` "Wello Horld!"
**False
```

```haskell
>>> **[0..] `isPrefixOf` [1..]
**False
```

```haskell
>>> **[0..] `isPrefixOf` [0..99]
**False
```

```haskell
>>> **[0..99] `isPrefixOf` [0..]
**True
```

```haskell
>>> **[0..] `isPrefixOf` [0..]
*** Hangs forever *
```

```haskell
>>> **isPrefixOf [] undefined
**True
```

--------------------------------

### splitAt laziness examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Demonstrates that the first component of splitAt is produced lazily.

```haskell
>>> **fst (splitAt 0 undefined)
**[]
```

```haskell
>>> **take 1 (fst (splitAt 10 (1 : undefined)))
**[1]
```

--------------------------------

### maximum examples

Source: https://hackage.haskell.org/package/base/docs/Data-List.html

Shows the behavior of maximum on a non-empty list, an empty list, and Nothing. The empty cases raise runtime exceptions.

```haskell
>>> maximum [1..10]
10
```

```haskell
>>> maximum []
*** Exception: Prelude.maximum: empty list
```

```haskell
>>> maximum Nothing
*** Exception: maximum: empty structure
```