Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

array: generalize S.takeLast and S.dropLast #630

Merged
merged 1 commit into from
Apr 27, 2019
Merged

array: generalize S.takeLast and S.dropLast #630

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
58 changes: 34 additions & 24 deletions index.js
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -3003,59 +3003,69 @@
impl: drop
};

//# takeLast :: Integer -> Array a -> Maybe (Array a)
//# takeLast :: (Applicative f, Foldable f, Monoid (f a)) => Integer -> f a -> Maybe (f a)
//.
//. Returns Just the last N elements of the given array if N is greater
//. than or equal to zero and less than or equal to the length of the array;
//. Returns Just the last N elements of the given structure if N is
//. non-negative and less than or equal to the size of the structure;
//. Nothing otherwise.
//.
//. ```javascript
//. > S.takeLast (2) (['a', 'b', 'c', 'd', 'e'])
//. Just (['d', 'e'])
//. > S.takeLast (0) (['foo', 'bar'])
//. Just ([])
//.
//. > S.takeLast (5) (['a', 'b', 'c', 'd', 'e'])
//. Just (['a', 'b', 'c', 'd', 'e'])
//. > S.takeLast (1) (['foo', 'bar'])
//. Just (['bar'])
//.
//. > S.takeLast (2) (['foo', 'bar'])
//. Just (['foo', 'bar'])
//.
//. > S.takeLast (6) (['a', 'b', 'c', 'd', 'e'])
//. > S.takeLast (3) (['foo', 'bar'])
//. Nothing
//.
//. > S.takeLast (3) (Cons (1) (Cons (2) (Cons (3) (Cons (4) (Nil)))))
//. Just (Cons (2) (Cons (3) (Cons (4) (Nil))))
//. ```
function takeLast(n) {
return function(xs) {
return n >= 0 && n <= xs.length ? Just (xs.slice (xs.length - n))
: Nothing;
return Z.map (Z.reverse, take (n) (Z.reverse (xs)));
};
}
_.takeLast = {
consts: {},
types: [$.Integer, $.Array (a), $.Maybe ($.Array (a))],
consts: {f: [Z.Applicative, Z.Foldable, Z.Monoid]},
types: [$.Integer, f (a), $.Maybe (f (a))],
impl: takeLast
};

//# dropLast :: Integer -> Array a -> Maybe (Array a)
//# dropLast :: (Applicative f, Foldable f, Monoid (f a)) => Integer -> f a -> Maybe (f a)
//.
//. Returns Just all but the last N elements of the given array if N is
//. greater than or equal to zero and less than or equal to the length of
//. the array; Nothing otherwise.
//. Returns Just all but the last N elements of the given structure if
//. N is non-negative and less than or equal to the size of the structure;
//. Nothing otherwise.
//.
//. ```javascript
//. > S.dropLast (2) (['a', 'b', 'c', 'd', 'e'])
//. Just (['a', 'b', 'c'])
//. > S.dropLast (0) (['foo', 'bar'])
//. Just (['foo', 'bar'])
//.
//. > S.dropLast (1) (['foo', 'bar'])
//. Just (['foo'])
//.
//. > S.dropLast (5) (['a', 'b', 'c', 'd', 'e'])
//. > S.dropLast (2) (['foo', 'bar'])
//. Just ([])
//.
//. > S.dropLast (6) (['a', 'b', 'c', 'd', 'e'])
//. > S.dropLast (3) (['foo', 'bar'])
//. Nothing
//.
//. > S.dropLast (3) (Cons (1) (Cons (2) (Cons (3) (Cons (4) (Nil)))))
//. Just (Cons (1) (Nil))
//. ```
function dropLast(n) {
return function(xs) {
return n >= 0 && n <= xs.length ? Just (xs.slice (0, xs.length - n))
: Nothing;
return Z.map (Z.reverse, drop (n) (Z.reverse (xs)));
};
}
_.dropLast = {
consts: {},
types: [$.Integer, $.Array (a), $.Maybe ($.Array (a))],
consts: {f: [Z.Applicative, Z.Foldable, Z.Monoid]},
types: [$.Integer, f (a), $.Maybe (f (a))],
impl: dropLast
};

Expand Down
13 changes: 11 additions & 2 deletions test/dropLast.js
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,15 +1,16 @@
'use strict';

const S = require ('..');
const S = require ('./internal/sanctuary');

const {Nil, Cons} = require ('./internal/List');
const eq = require ('./internal/eq');


test ('dropLast', () => {

eq (typeof S.dropLast) ('function');
eq (S.dropLast.length) (1);
eq (S.show (S.dropLast)) ('dropLast :: Integer -> Array a -> Maybe (Array a)');
eq (S.show (S.dropLast)) ('dropLast :: (Applicative f, Foldable f, Monoid f) => Integer -> f a -> Maybe (f a)');

eq (S.dropLast (0) ([1, 2, 3, 4, 5])) (S.Just ([1, 2, 3, 4, 5]));
eq (S.dropLast (1) ([1, 2, 3, 4, 5])) (S.Just ([1, 2, 3, 4]));
Expand All @@ -21,4 +22,12 @@ test ('dropLast', () => {

eq (S.dropLast (-1) ([1, 2, 3, 4, 5])) (S.Nothing);

eq (S.dropLast (0) (Cons (1) (Cons (2) (Cons (3) (Nil))))) (S.Just (Cons (1) (Cons (2) (Cons (3) (Nil)))));
eq (S.dropLast (1) (Cons (1) (Cons (2) (Cons (3) (Nil))))) (S.Just (Cons (1) (Cons (2) (Nil))));
eq (S.dropLast (2) (Cons (1) (Cons (2) (Cons (3) (Nil))))) (S.Just (Cons (1) (Nil)));
eq (S.dropLast (3) (Cons (1) (Cons (2) (Cons (3) (Nil))))) (S.Just (Nil));
eq (S.dropLast (4) (Cons (1) (Cons (2) (Cons (3) (Nil))))) (S.Nothing);

eq (S.dropLast (-1) (Cons (1) (Cons (2) (Cons (3) (Nil))))) (S.Nothing);

});
13 changes: 11 additions & 2 deletions test/takeLast.js
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,15 +1,16 @@
'use strict';

const S = require ('..');
const S = require ('./internal/sanctuary');

const {Nil, Cons} = require ('./internal/List');
const eq = require ('./internal/eq');


test ('takeLast', () => {

eq (typeof S.takeLast) ('function');
eq (S.takeLast.length) (1);
eq (S.show (S.takeLast)) ('takeLast :: Integer -> Array a -> Maybe (Array a)');
eq (S.show (S.takeLast)) ('takeLast :: (Applicative f, Foldable f, Monoid f) => Integer -> f a -> Maybe (f a)');

eq (S.takeLast (0) ([1, 2, 3, 4, 5])) (S.Just ([]));
eq (S.takeLast (1) ([1, 2, 3, 4, 5])) (S.Just ([5]));
Expand All @@ -21,4 +22,12 @@ test ('takeLast', () => {

eq (S.takeLast (-1) ([1, 2, 3, 4, 5])) (S.Nothing);

eq (S.takeLast (0) (Cons (1) (Cons (2) (Cons (3) (Nil))))) (S.Just (Nil));
eq (S.takeLast (1) (Cons (1) (Cons (2) (Cons (3) (Nil))))) (S.Just (Cons (3) (Nil)));
eq (S.takeLast (2) (Cons (1) (Cons (2) (Cons (3) (Nil))))) (S.Just (Cons (2) (Cons (3) (Nil))));
eq (S.takeLast (3) (Cons (1) (Cons (2) (Cons (3) (Nil))))) (S.Just (Cons (1) (Cons (2) (Cons (3) (Nil)))));
eq (S.takeLast (4) (Cons (1) (Cons (2) (Cons (3) (Nil))))) (S.Nothing);

eq (S.takeLast (-1) (Cons (1) (Cons (2) (Cons (3) (Nil))))) (S.Nothing);

});