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dash.el

A modern list api for Emacs. No 'cl required.

Installation

It's available on marmalade and Melpa:

M-x package-install dash

Or you can just dump dash.el in your load path somewhere.

Functions

-map (fn list)
-reduce-from (fn initial-value list)
-reduce-r-from (fn initial-value list)
-reduce (fn list)
-reduce-r (fn list)
-filter (pred list)
-remove (pred list)
-keep (fn list)
-map-when (pred rep list)
-map-indexed (fn list)
-flatten (l)
-concat (&rest lists)
-mapcat (fn list)
-cons* (&rest args)
-count (pred list)
-sum (list)
-product (list)
-min (x &rest xs)
-min-by (pred list)
-max (x &rest xs)
-max-by (pred list)
-any? (pred list)
-all? (pred list)
-none? (pred list)
-only-some? (pred list)
-each (list fn)
-each-while (list pred fn)
-dotimes (num fn)
-repeat (n x)
-slice (list from &optional to)
-take (n list)
-drop (n list)
-take-while (pred list)
-drop-while (pred list)
-split-at (n list)
-rotate (n list)
-insert-at (n x list)
-split-with (pred list)
-separate (pred list)
-partition (n list)
-partition-all-in-steps (n step list)
-partition-in-steps (n step list)
-partition-all (n list)
-partition-by (fn list)
-partition-by-header (fn list)
-group-by (fn list)
-interpose (sep list)
-interleave (&rest lists)
-zip-with (fn list1 list2)
-zip (list1 list2)
-first (pred list)
-last (pred list)
-first-item (list)
-last-item (list)
-union (list list2)
-difference (list list2)
-intersection (list list2)
-distinct (list)
-contains? (list element)
-sort (predicate list)
-> (x &optional form &rest more)
->> (x form &rest more)
--> (x form &rest more)
-when-let (var-val &rest body)
-when-let* (vars-vals &rest body)
-if-let (var-val then &optional else)
-if-let* (vars-vals then &optional else)
-partial (fn &rest args)
-rpartial (fn &rest args)
-juxt (&rest fns)
-applify (fn)
-on (operator transformer)
-flip (func)
-const (c)
-cut (&rest params)
-not (pred)
-orfn (&rest preds)
-andfn (&rest preds)
!cons (car cdr)
!cdr (list)

There are also anaphoric versions of these functions where that makes sense, prefixed with two dashes instead of one.

Anaphoric functions

While -map takes a function to map over the list, you can also use the anaphoric form with double dashes - which will then be executed with it exposed as the list item. Here's an example:

(-map (lambda (n) (* n n)) '(1 2 3 4)) ;; normal version

(--map (* it it) '(1 2 3 4)) ;; anaphoric version

of course the original can also be written like

(defun square (n) (* n n))

(-map 'square '(1 2 3 4))

which demonstrates the usefulness of both versions.

Documentation and examples

-map `(fn list)`

Returns a new list consisting of the result of applying fn to the items in list.

(-map (lambda (num) (* num num)) '(1 2 3 4)) ;; => '(1 4 9 16)
(-map 'square '(1 2 3 4)) ;; => '(1 4 9 16)
(--map (* it it) '(1 2 3 4)) ;; => '(1 4 9 16)

-reduce-from `(fn initial-value list)`

Returns the result of applying fn to initial-value and the first item in list, then applying fn to that result and the 2nd item, etc. If list contains no items, returns initial-value and fn is not called.

In the anaphoric form --reduce-from, the accumulated value is exposed as acc.

(-reduce-from '- 10 '(1 2 3)) ;; => 4
(-reduce-from (lambda (memo item) (concat "(" memo " - " (int-to-string item) ")")) "10" '(1 2 3)) ;; => "(((10 - 1) - 2) - 3)"
(--reduce-from (concat acc " " it) "START" '("a" "b" "c")) ;; => "START a b c"

-reduce-r-from `(fn initial-value list)`

Replace conses with fn, nil with initial-value and evaluate the resulting expression. If list is empty, initial-value is returned and fn is not called.

Note: this function works the same as -reduce-from but the operation associates from right instead of from left.

(-reduce-r-from '- 10 '(1 2 3)) ;; => -8
(-reduce-r-from (lambda (item memo) (concat "(" (int-to-string item) " - " memo ")")) "10" '(1 2 3)) ;; => "(1 - (2 - (3 - 10)))"
(--reduce-r-from (concat it " " acc) "END" '("a" "b" "c")) ;; => "a b c END"

-reduce `(fn list)`

Returns the result of applying fn to the first 2 items in list, then applying fn to that result and the 3rd item, etc. If list contains no items, fn must accept no arguments as well, and reduce returns the result of calling fn with no arguments. If list has only 1 item, it is returned and fn is not called.

In the anaphoric form --reduce, the accumulated value is exposed as acc.

(-reduce '- '(1 2 3 4)) ;; => -8
(-reduce (lambda (memo item) (format "%s-%s" memo item)) '(1 2 3)) ;; => "1-2-3"
(--reduce (format "%s-%s" acc it) '(1 2 3)) ;; => "1-2-3"

-reduce-r `(fn list)`

Replace conses with fn and evaluate the resulting expression. The final nil is ignored. If list contains no items, fn must accept no arguments as well, and reduce returns the result of calling fn with no arguments. If list has only 1 item, it is returned and fn is not called.

The first argument of fn is the new item, the second is the accumulated value.

Note: this function works the same as -reduce but the operation associates from right instead of from left.

(-reduce-r '- '(1 2 3 4)) ;; => -2
(-reduce-r (lambda (item memo) (format "%s-%s" memo item)) '(1 2 3)) ;; => "3-2-1"
(--reduce-r (format "%s-%s" acc it) '(1 2 3)) ;; => "3-2-1"

-filter `(pred list)`

Returns a new list of the items in list for which pred returns a non-nil value.

Alias: -select

(-filter (lambda (num) (= 0 (% num 2))) '(1 2 3 4)) ;; => '(2 4)
(-filter 'even? '(1 2 3 4)) ;; => '(2 4)
(--filter (= 0 (% it 2)) '(1 2 3 4)) ;; => '(2 4)

-remove `(pred list)`

Returns a new list of the items in list for which pred returns nil.

Alias: -reject

(-remove (lambda (num) (= 0 (% num 2))) '(1 2 3 4)) ;; => '(1 3)
(-remove 'even? '(1 2 3 4)) ;; => '(1 3)
(--remove (= 0 (% it 2)) '(1 2 3 4)) ;; => '(1 3)

-keep `(fn list)`

Returns a new list of the non-nil results of applying fn to the items in list.

(-keep 'cdr '((1 2 3) (4 5) (6))) ;; => '((2 3) (5))
(-keep (lambda (num) (when (> num 3) (* 10 num))) '(1 2 3 4 5 6)) ;; => '(40 50 60)
(--keep (when (> it 3) (* 10 it)) '(1 2 3 4 5 6)) ;; => '(40 50 60)

-map-when `(pred rep list)`

Returns a new list where the elements in list that does not match the pred function are unchanged, and where the elements in list that do match the pred function are mapped through the rep function.

(-map-when 'even? 'square '(1 2 3 4)) ;; => '(1 4 3 16)
(--map-when (> it 2) (* it it) '(1 2 3 4)) ;; => '(1 2 9 16)
(--map-when (= it 2) 17 '(1 2 3 4)) ;; => '(1 17 3 4)

-map-indexed `(fn list)`

Returns a new list consisting of the result of (fn index item) for each item in list.

In the anaphoric form --map-indexed, the index is exposed as it-index.

(-map-indexed (lambda (index item) (- item index)) '(1 2 3 4)) ;; => '(1 1 1 1)
(--map-indexed (- it it-index) '(1 2 3 4)) ;; => '(1 1 1 1)

-flatten `(l)`

Takes a nested list l and returns its contents as a single, flat list.

(-flatten '((1))) ;; => '(1)
(-flatten '((1 (2 3) (((4 (5))))))) ;; => '(1 2 3 4 5)
(-flatten '(1 2 (3 . 4))) ;; => '(1 2 (3 . 4))

-concat `(&rest lists)`

Returns a new list with the concatenation of the elements in the supplied lists.

(-concat '(1)) ;; => '(1)
(-concat '(1) '(2)) ;; => '(1 2)
(-concat '(1) '(2 3) '(4)) ;; => '(1 2 3 4)

-mapcat `(fn list)`

Returns the concatenation of the result of mapping fn over list. Thus function fn should return a list.

(-mapcat 'list '(1 2 3)) ;; => '(1 2 3)
(-mapcat (lambda (item) (list 0 item)) '(1 2 3)) ;; => '(0 1 0 2 0 3)
(--mapcat (list 0 it) '(1 2 3)) ;; => '(0 1 0 2 0 3)

-cons* `(&rest args)`

Makes a new list from the elements of args.

The last 2 members of args are used as the final cons of the result so if the final member of args is not a list the result is a dotted list.

(-cons* 1 2) ;; => '(1 . 2)
(-cons* 1 2 3) ;; => '(1 2 . 3)
(-cons* 1) ;; => 1

-count `(pred list)`

Counts the number of items in list where (pred item) is non-nil.

(-count 'even? '(1 2 3 4 5)) ;; => 2
(--count (< it 4) '(1 2 3 4)) ;; => 3

-sum `(list)`

Return the sum of list.

(-sum '()) ;; => 0
(-sum '(1)) ;; => 1
(-sum '(1 2 3)) ;; => 6

-product `(list)`

Return the product of list.

(-product '()) ;; => 1
(-product '(1)) ;; => 1
(-product '(1 2 3)) ;; => 6

-min `(x &rest xs)`

Return the smallest value of all arguments.

(-min 0) ;; => 0
(-min 1) ;; => 1
(-min 1 2 3) ;; => 1

-min-by `(pred list)`

Call pred for each item in list and return item with smallest value.

(-min-by 'identity '()) ;; => nil
(-min-by 'identity '(1)) ;; => 1
(--min-by (cdr it) '((a . 1) (b . 2) (c . 3))) ;; => '(a . 1)

-max `(x &rest xs)`

Return the largest value of all arguments.

(-max 0) ;; => 0
(-max 1) ;; => 1
(-max 1 2 3) ;; => 3

-max-by `(pred list)`

Call pred for each item in list and return item with largest value.

(-max-by 'identity '()) ;; => nil
(-max-by 'identity '(1)) ;; => 1
(--max-by (cdr it) '((a . 1) (b . 2) (c . 3))) ;; => '(c . 3)

-any? `(pred list)`

Returns t if (pred x) is non-nil for any x in list, else nil.

Alias: -some?

(-any? 'even? '(1 2 3)) ;; => t
(-any? 'even? '(1 3 5)) ;; => nil
(--any? (= 0 (% it 2)) '(1 2 3)) ;; => t

-all? `(pred list)`

Returns t if (pred x) is non-nil for all x in list, else nil.

Alias: -every?

(-all? 'even? '(1 2 3)) ;; => nil
(-all? 'even? '(2 4 6)) ;; => t
(--all? (= 0 (% it 2)) '(2 4 6)) ;; => t

-none? `(pred list)`

Returns t if (pred x) is nil for all x in list, else nil.

(-none? 'even? '(1 2 3)) ;; => nil
(-none? 'even? '(1 3 5)) ;; => t
(--none? (= 0 (% it 2)) '(1 2 3)) ;; => nil

-only-some? `(pred list)`

Returns t if there is a mix of items in list that matches and does not match pred. Returns nil both if all items match the predicate, and if none of the items match the predicate.

(-only-some? 'even? '(1 2 3)) ;; => t
(-only-some? 'even? '(1 3 5)) ;; => nil
(-only-some? 'even? '(2 4 6)) ;; => nil

-each `(list fn)`

Calls fn with every item in list. Returns nil, used for side-effects only.

(let (s) (-each '(1 2 3) (lambda (item) (setq s (cons item s))))) ;; => nil
(let (s) (-each '(1 2 3) (lambda (item) (setq s (cons item s)))) s) ;; => '(3 2 1)
(let (s) (--each '(1 2 3) (setq s (cons it s))) s) ;; => '(3 2 1)

-each-while `(list pred fn)`

Calls fn with every item in list while (pred item) is non-nil. Returns nil, used for side-effects only.

(let (s) (-each-while '(2 4 5 6) 'even? (lambda (item) (!cons item s))) s) ;; => '(4 2)
(let (s) (--each-while '(1 2 3 4) (< it 3) (!cons it s)) s) ;; => '(2 1)

-dotimes `(num fn)`

Repeatedly calls fn (presumably for side-effects) passing in integers from 0 through n-1.

(let (s) (-dotimes 3 (lambda (n) (!cons n s))) s) ;; => '(2 1 0)
(let (s) (--dotimes 5 (!cons it s)) s) ;; => '(4 3 2 1 0)

-repeat `(n x)`

Return a list with x repeated n times. Returns nil if n is less than 1.

(-repeat 3 :a) ;; => '(:a :a :a)
(-repeat 1 :a) ;; => '(:a)
(-repeat 0 :a) ;; => nil

-slice `(list from &optional to)`

Return copy of list, starting from index from to index to. from or to may be negative.

(-slice '(1 2 3 4 5) 1) ;; => '(2 3 4 5)
(-slice '(1 2 3 4 5) 0 3) ;; => '(1 2 3)
(-slice '(1 2 3 4 5) 1 -1) ;; => '(2 3 4)

-take `(n list)`

Returns a new list of the first n items in list, or all items if there are fewer than n.

(-take 3 '(1 2 3 4 5)) ;; => '(1 2 3)
(-take 17 '(1 2 3 4 5)) ;; => '(1 2 3 4 5)

-drop `(n list)`

Returns the tail of list without the first n items.

(-drop 3 '(1 2 3 4 5)) ;; => '(4 5)
(-drop 17 '(1 2 3 4 5)) ;; => '()

-take-while `(pred list)`

Returns a new list of successive items from list while (pred item) returns a non-nil value.

(-take-while 'even? '(1 2 3 4)) ;; => '()
(-take-while 'even? '(2 4 5 6)) ;; => '(2 4)
(--take-while (< it 4) '(1 2 3 4 3 2 1)) ;; => '(1 2 3)

-drop-while `(pred list)`

Returns the tail of list starting from the first item for which (pred item) returns nil.

(-drop-while 'even? '(1 2 3 4)) ;; => '(1 2 3 4)
(-drop-while 'even? '(2 4 5 6)) ;; => '(5 6)
(--drop-while (< it 4) '(1 2 3 4 3 2 1)) ;; => '(4 3 2 1)

-split-at `(n list)`

Returns a list of ((-take n list) (-drop n list)), in no more than one pass through the list.

(-split-at 3 '(1 2 3 4 5)) ;; => '((1 2 3) (4 5))
(-split-at 17 '(1 2 3 4 5)) ;; => '((1 2 3 4 5) nil)

-rotate `(n list)`

Rotate list n places to the right. With n negative, rotate to the left. The time complexity is o(n).

(-rotate 3 '(1 2 3 4 5 6 7)) ;; => '(5 6 7 1 2 3 4)
(-rotate -3 '(1 2 3 4 5 6 7)) ;; => '(4 5 6 7 1 2 3)

-insert-at `(n x list)`

Returns a list with x inserted into list at position n.

(-insert-at 1 'x '(a b c)) ;; => '(a x b c)
(-insert-at 12 'x '(a b c)) ;; => '(a b c x)

-split-with `(pred list)`

Returns a list of ((-take-while pred list) (-drop-while pred list)), in no more than one pass through the list.

(-split-with 'even? '(1 2 3 4)) ;; => '(nil (1 2 3 4))
(-split-with 'even? '(2 4 5 6)) ;; => '((2 4) (5 6))
(--split-with (< it 4) '(1 2 3 4 3 2 1)) ;; => '((1 2 3) (4 3 2 1))

-separate `(pred list)`

Returns a list of ((-filter pred list) (-remove pred list)), in one pass through the list.

(-separate (lambda (num) (= 0 (% num 2))) '(1 2 3 4 5 6 7)) ;; => '((2 4 6) (1 3 5 7))
(--separate (< it 5) '(3 7 5 9 3 2 1 4 6)) ;; => '((3 3 2 1 4) (7 5 9 6))
(-separate 'cdr '((1 2) (1) (1 2 3) (4))) ;; => '(((1 2) (1 2 3)) ((1) (4)))

-partition `(n list)`

Returns a new list with the items in list grouped into n-sized sublists. If there are not enough items to make the last group n-sized, those items are discarded.

(-partition 2 '(1 2 3 4 5 6)) ;; => '((1 2) (3 4) (5 6))
(-partition 2 '(1 2 3 4 5 6 7)) ;; => '((1 2) (3 4) (5 6))
(-partition 3 '(1 2 3 4 5 6 7)) ;; => '((1 2 3) (4 5 6))

-partition-all-in-steps `(n step list)`

Returns a new list with the items in list grouped into n-sized sublists at offsets step apart. The last groups may contain less than n items.

(-partition-all-in-steps 2 1 '(1 2 3 4)) ;; => '((1 2) (2 3) (3 4) (4))
(-partition-all-in-steps 3 2 '(1 2 3 4)) ;; => '((1 2 3) (3 4))
(-partition-all-in-steps 3 2 '(1 2 3 4 5)) ;; => '((1 2 3) (3 4 5) (5))

-partition-in-steps `(n step list)`

Returns a new list with the items in list grouped into n-sized sublists at offsets step apart. If there are not enough items to make the last group n-sized, those items are discarded.

(-partition-in-steps 2 1 '(1 2 3 4)) ;; => '((1 2) (2 3) (3 4))
(-partition-in-steps 3 2 '(1 2 3 4)) ;; => '((1 2 3))
(-partition-in-steps 3 2 '(1 2 3 4 5)) ;; => '((1 2 3) (3 4 5))

-partition-all `(n list)`

Returns a new list with the items in list grouped into n-sized sublists. The last group may contain less than n items.

(-partition-all 2 '(1 2 3 4 5 6)) ;; => '((1 2) (3 4) (5 6))
(-partition-all 2 '(1 2 3 4 5 6 7)) ;; => '((1 2) (3 4) (5 6) (7))
(-partition-all 3 '(1 2 3 4 5 6 7)) ;; => '((1 2 3) (4 5 6) (7))

-partition-by `(fn list)`

Applies fn to each item in list, splitting it each time fn returns a new value.

(-partition-by 'even? '()) ;; => '()
(-partition-by 'even? '(1 1 2 2 2 3 4 6 8)) ;; => '((1 1) (2 2 2) (3) (4 6 8))
(--partition-by (< it 3) '(1 2 3 4 3 2 1)) ;; => '((1 2) (3 4 3) (2 1))

-partition-by-header `(fn list)`

Applies fn to the first item in list. That is the header value. Applies fn to each item in list, splitting it each time fn returns the header value, but only after seeing at least one other value (the body).

(--partition-by-header (= it 1) '(1 2 3 1 2 1 2 3 4)) ;; => '((1 2 3) (1 2) (1 2 3 4))
(--partition-by-header (> it 0) '(1 2 0 1 0 1 2 3 0)) ;; => '((1 2 0) (1 0) (1 2 3 0))
(-partition-by-header 'even? '(2 1 1 1 4 1 3 5 6 6 1)) ;; => '((2 1 1 1) (4 1 3 5) (6 6 1))

-group-by `(fn list)`

Separate list into an alist whose keys are fn applied to the elements of list. Keys are compared by equal.

(-group-by 'even? '()) ;; => '()
(-group-by 'even? '(1 1 2 2 2 3 4 6 8)) ;; => '((nil 1 1 3) (t 2 2 2 4 6 8))
(--group-by (car (split-string it "/")) '("a/b" "c/d" "a/e")) ;; => '(("a" "a/b" "a/e") ("c" "c/d"))

-interpose `(sep list)`

Returns a new list of all elements in list separated by sep.

(-interpose "-" '()) ;; => '()
(-interpose "-" '("a")) ;; => '("a")
(-interpose "-" '("a" "b" "c")) ;; => '("a" "-" "b" "-" "c")

-interleave `(&rest lists)`

Returns a new list of the first item in each list, then the second etc.

(-interleave '(1 2) '("a" "b")) ;; => '(1 "a" 2 "b")
(-interleave '(1 2) '("a" "b") '("A" "B")) ;; => '(1 "a" "A" 2 "b" "B")
(-interleave '(1 2 3) '("a" "b")) ;; => '(1 "a" 2 "b")

-zip-with `(fn list1 list2)`

Zip the two lists list1 and list2 using a function fn. This function is applied pairwise taking as first argument element of list1 and as second argument element of list2 at corresponding position.

The anaphoric form --zip-with binds the elements from list1 as it, and the elements from list2 as other.

(-zip-with '+ '(1 2 3) '(4 5 6)) ;; => '(5 7 9)
(-zip-with 'cons '(1 2 3) '(4 5 6)) ;; => '((1 . 4) (2 . 5) (3 . 6))
(--zip-with (concat it " and " other) '("Batman" "Jekyll") '("Robin" "Hyde")) ;; => '("Batman and Robin" "Jekyll and Hyde")

-zip `(list1 list2)`

Zip the two lists together. Return the list where elements are cons pairs with car being element from list1 and cdr being element from list2. The length of the returned list is the length of the shorter one.

(-zip '(1 2 3) '(4 5 6)) ;; => '((1 . 4) (2 . 5) (3 . 6))
(-zip '(1 2 3) '(4 5 6 7)) ;; => '((1 . 4) (2 . 5) (3 . 6))
(-zip '(1 2 3 4) '(4 5 6)) ;; => '((1 . 4) (2 . 5) (3 . 6))

-first `(pred list)`

Returns the first x in list where (pred x) is non-nil, else nil.

To get the first item in the list no questions asked, use car.

(-first 'even? '(1 2 3)) ;; => 2
(-first 'even? '(1 3 5)) ;; => nil
(--first (> it 2) '(1 2 3)) ;; => 3

-last `(pred list)`

Return the last x in list where (pred x) is non-nil, else nil.

(-last 'even? '(1 2 3 4 5 6 3 3 3)) ;; => 6
(-last 'even? '(1 3 7 5 9)) ;; => nil
(--last (> (length it) 3) '("a" "looong" "word" "and" "short" "one")) ;; => "short"

-first-item `(list)`

Returns the first item of list, or nil on an empty list.

(-first-item '(1 2 3)) ;; => 1
(-first-item nil) ;; => nil

-last-item `(list)`

Returns the first item of list, or nil on an empty list.

(-last-item '(1 2 3)) ;; => 3
(-last-item nil) ;; => nil

-union `(list list2)`

Return a new list containing the elements of list1 and elements of list2 that are not in list1. The test for equality is done with equal, or with -compare-fn if that's non-nil.

(-union '(1 2 3) '(3 4 5)) ;; => '(1 2 3 4 5)
(-union '(1 2 3 4) '()) ;; => '(1 2 3 4)
(-union '(1 1 2 2) '(3 2 1)) ;; => '(1 1 2 2 3)

-difference `(list list2)`

Return a new list with only the members of list that are not in list2. The test for equality is done with equal, or with -compare-fn if that's non-nil.

(-difference '() '()) ;; => '()
(-difference '(1 2 3) '(4 5 6)) ;; => '(1 2 3)
(-difference '(1 2 3 4) '(3 4 5 6)) ;; => '(1 2)

-intersection `(list list2)`

Return a new list containing only the elements that are members of both list and list2. The test for equality is done with equal, or with -compare-fn if that's non-nil.

(-intersection '() '()) ;; => '()
(-intersection '(1 2 3) '(4 5 6)) ;; => '()
(-intersection '(1 2 3 4) '(3 4 5 6)) ;; => '(3 4)

-distinct `(list)`

Return a new list with all duplicates removed. The test for equality is done with equal, or with -compare-fn if that's non-nil.

Alias: -uniq

(-distinct '()) ;; => '()
(-distinct '(1 2 2 4)) ;; => '(1 2 4)

-contains? `(list element)`

Return whether list contains element. The test for equality is done with equal, or with -compare-fn if that's non-nil.

(-contains? '(1 2 3) 1) ;; => t
(-contains? '(1 2 3) 2) ;; => t
(-contains? '(1 2 3) 4) ;; => nil

-sort `(predicate list)`

Sort list, stably, comparing elements using predicate. Returns the sorted list. list is not modified by side effects. predicate is called with two elements of list, and should return non-nil if the first element should sort before the second.

(-sort '< '(3 1 2)) ;; => '(1 2 3)
(-sort '> '(3 1 2)) ;; => '(3 2 1)
(--sort (< it other) '(3 1 2)) ;; => '(1 2 3)

-> `(x &optional form &rest more)`

Threads the expr through the forms. Inserts x as the second item in the first form, making a list of it if it is not a list already. If there are more forms, inserts the first form as the second item in second form, etc.

(-> "Abc") ;; => "Abc"
(-> "Abc" (concat "def")) ;; => "Abcdef"
(-> "Abc" (concat "def") (concat "ghi")) ;; => "Abcdefghi"

->> `(x form &rest more)`

Threads the expr through the forms. Inserts x as the last item in the first form, making a list of it if it is not a list already. If there are more forms, inserts the first form as the last item in second form, etc.

(->> "Abc" (concat "def")) ;; => "defAbc"
(->> "Abc" (concat "def") (concat "ghi")) ;; => "ghidefAbc"
(->> 5 (- 8)) ;; => 3

--> `(x form &rest more)`

Threads the expr through the forms. Inserts x at the position signified by the token it in the first form. If there are more forms, inserts the first form at the position signified by it in in second form, etc.

(--> "def" (concat "abc" it "ghi")) ;; => "abcdefghi"
(--> "def" (concat "abc" it "ghi") (upcase it)) ;; => "ABCDEFGHI"
(--> "def" (concat "abc" it "ghi") upcase) ;; => "ABCDEFGHI"

-when-let `(var-val &rest body)`

If val evaluates to non-nil, bind it to var and execute body. var-val should be a (var val) pair.

(-when-let (match-index (string-match "d" "abcd")) (+ match-index 2)) ;; => 5
(--when-let (member :b '(:a :b :c)) (cons :d it)) ;; => '(:d :b :c)
(--when-let (even? 3) (cat it :a)) ;; => nil

-when-let* `(vars-vals &rest body)`

If all vals evaluate to true, bind them to their corresponding vars and execute body. vars-vals should be a list of (var val) pairs (corresponding to bindings of let*).

(-when-let* ((x 5) (y 3) (z (+ y 4))) (+ x y z)) ;; => 15
(-when-let* ((x 5) (y nil) (z 7)) (+ x y z)) ;; => nil

-if-let `(var-val then &optional else)`

If val evaluates to non-nil, bind it to var and do then, otherwise do else. var-val should be a (var val) pair.

(-if-let (match-index (string-match "d" "abc")) (+ match-index 3) 7) ;; => 7
(--if-let (even? 4) it nil) ;; => t

-if-let* `(vars-vals then &optional else)`

If all vals evaluate to true, bind them to their corresponding vars and do then, otherwise do else. vars-vals should be a list of (var val) pairs (corresponding to the bindings of let*).

(-if-let* ((x 5) (y 3) (z 7)) (+ x y z) "foo") ;; => 15
(-if-let* ((x 5) (y nil) (z 7)) (+ x y z) "foo") ;; => "foo"

-partial `(fn &rest args)`

Takes a function fn and fewer than the normal arguments to fn, and returns a fn that takes a variable number of additional args. When called, the returned function calls fn with args first and then additional args.

(funcall (-partial '- 5) 3) ;; => 2
(funcall (-partial '+ 5 2) 3) ;; => 10

-rpartial `(fn &rest args)`

Requires Emacs 24 or higher.

(funcall (-rpartial '- 5) 8) ;; => 3
(funcall (-rpartial '- 5 2) 10) ;; => 3

-juxt `(&rest fns)`

Takes a list of functions and returns a fn that is the juxtaposition of those fns. The returned fn takes a variable number of args, and returns a list containing the result of applying each fn to the args (left-to-right).

Requires Emacs 24 or higher.

(funcall (-juxt '+ '-) 3 5) ;; => '(8 -2)
(-map (-juxt 'identity 'square) '(1 2 3)) ;; => '((1 1) (2 4) (3 9))

-applify `(fn)`

Changes an n-arity function fn to a 1-arity function that expects a list with n items as arguments

(-map (-applify '+) '((1 1 1) (1 2 3) (5 5 5))) ;; => '(3 6 15)
(-map (-applify (lambda (a b c) (\` ((\, a) ((\, b) ((\, c))))))) '((1 1 1) (1 2 3) (5 5 5))) ;; => '((1 (1 (1))) (1 (2 (3))) (5 (5 (5))))
(funcall (-applify '<) '(3 6)) ;; => t

-on `(operator transformer)`

Return a function of two arguments that first applies transformer to each of them and then applies operator on the results (in the same order).

In types: (b -> b -> c) -> (a -> b) -> a -> a -> c

(-sort (-on '< 'length) '((1 2 3) (1) (1 2))) ;; => '((1) (1 2) (1 2 3))
(-sort (-on 'string-lessp 'int-to-string) '(10 12 1 2 22)) ;; => '(1 10 12 2 22)
(funcall (-on '+ '1+) 1 2) ;; => 5

-flip `(func)`

Swap the order of arguments for binary function func.

In types: (a -> b -> c) -> b -> a -> c

(funcall (-flip '<) 2 1) ;; => t
(funcall (-flip '-) 3 8) ;; => 5
(-sort (-flip '<) '(4 3 6 1)) ;; => '(6 4 3 1)

-const `(c)`

Return a function that returns c ignoring any additional arguments.

In types: a -> b -> a

(funcall (-const 2) 1 3 "foo") ;; => 2
(-map (-const 1) '("a" "b" "c" "d")) ;; => '(1 1 1 1)
(-sum (-map (-const 1) '("a" "b" "c" "d"))) ;; => 4

-cut `(&rest params)`

Take n-ary function and n arguments and specialize some of them. Arguments denoted by <> will be left unspecialized.

See srfi-26 for detailed description.

(funcall (-cut list 1 <> 3 <> 5) 2 4) ;; => '(1 2 3 4 5)
(-map (-cut funcall <> 5) '(1+ 1- (lambda (x) (/ 1.0 x)))) ;; => '(6 4 0.2)
(-filter (-cut < <> 5) '(1 3 5 7 9)) ;; => '(1 3)

-not `(pred)`

Take an unary predicates pred and return an unary predicate that returns t if pred returns nil and nil if pred returns non-nil.

(funcall (-not 'even?) 5) ;; => t
(-filter (-not (-partial '< 4)) '(1 2 3 4 5 6 7 8)) ;; => '(1 2 3 4)

-orfn `(&rest preds)`

Take list of unary predicates preds and return an unary predicate with argument x that returns non-nil if at least one of the preds returns non-nil on x.

In types: [a -> Bool] -> a -> Bool

(-filter (-orfn 'even? (-partial (-flip '<) 5)) '(1 2 3 4 5 6 7 8 9 10)) ;; => '(1 2 3 4 6 8 10)
(funcall (-orfn 'stringp 'even?) "foo") ;; => t

-andfn `(&rest preds)`

Take list of unary predicates preds and return an unary predicate with argument x that returns non-nil if all of the preds returns non-nil on x.

In types: [a -> Bool] -> a -> Bool

(funcall (-andfn (-cut < <> 10) 'even?) 6) ;; => t
(funcall (-andfn (-cut < <> 10) 'even?) 12) ;; => nil
(-filter (-andfn (-not 'even?) (-cut >= 5 <>)) '(1 2 3 4 5 6 7 8 9 10)) ;; => '(1 3 5)

!cons `(car cdr)`

Destructive: Sets cdr to the cons of car and cdr.

(let (l) (!cons 5 l) l) ;; => '(5)
(let ((l '(3))) (!cons 5 l) l) ;; => '(5 3)

!cdr `(list)`

Destructive: Sets list to the cdr of list.

(let ((l '(3))) (!cdr l) l) ;; => '()
(let ((l '(3 5))) (!cdr l) l) ;; => '(5)

Contribute

Yes, please do. Pure functions in the list manipulation realm only, please. There's a suite of tests in dev/examples.el, so remember to add tests for your function, or I might break it later.

You'll find the repo at:

https://github.com/magnars/dash.el

Run the tests with

./run-tests.sh

Create the docs with

./create-docs.sh

I highly recommend that you install these as a pre-commit hook, so that the tests are always running and the docs are always in sync:

cp pre-commit.sh .git/hooks/pre-commit

Oh, and don't edit README.md directly, it is auto-generated. Change readme-template.md or examples-to-docs.el instead.

Changelist

From 1.7.0 to 1.8.0

Add -first-item and -last-item (Wilfred Hughes)

From 1.6.0 to 1.7.0

Add -rotate (Matus Goljer)

From 1.5.0 to 1.6.0

Add -min, -max, -min-by and -max-by (Johan Andersson)

From 1.4.0 to 1.5.0

Add -sum and -product (Johan Andersson)

From 1.3.0 to 1.4.0

Add -sort
Add -reduce-r (Matus Goljer)
Add -reduce-r-from (Matus Goljer)

From 1.2.0 to 1.3.0

Add -partition-in-steps
Add -partition-all-in-steps

From 1.1.0 to 1.2.0

Add -last (Matus Goljer)
Add -insert-at (Emanuel Evans)
Add -when-let and -if-let (Emanuel Evans)
Add -when-let* and -if-let* (Emanuel Evans)
Some bugfixes

Contributors

Matus Goljer contributed -union, -separate, -zip, -zip-with, -reduce-r, -reduce-r-from and -rotate.
Takafumi Arakaki contributed -group-by.
tali713 is the author of -applify.
Víctor M. Valenzuela contributed -repeat.
Nic Ferrier contributed -cons*.
Wilfred Hughes contributed -slice, -first-item and -last-item.
Emanuel Evans contributed -if-let, -when-let and -insert-at.
Johan Andersson contributed -sum, -product, -min, -max, -min-by and -max-by.

Thanks!

License

Authors: Magnar Sveen magnars@gmail.com Keywords: lists

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.

33 KiB Raw Blame History

dash.el

Installation

Functions

Anaphoric functions

Documentation and examples

-map (fn list)

-reduce-from (fn initial-value list)

-reduce-r-from (fn initial-value list)

-reduce (fn list)

-reduce-r (fn list)

-filter (pred list)

-remove (pred list)

-keep (fn list)

-map-when (pred rep list)

-map-indexed (fn list)

-flatten (l)

-concat (&rest lists)

-mapcat (fn list)

-cons* (&rest args)

-count (pred list)

-sum (list)

-product (list)

-min (x &rest xs)

-min-by (pred list)

-max (x &rest xs)

-max-by (pred list)

-any? (pred list)

-all? (pred list)

-none? (pred list)

-only-some? (pred list)

-each (list fn)

-each-while (list pred fn)

-dotimes (num fn)

-repeat (n x)

-slice (list from &optional to)

-take (n list)

-drop (n list)

-take-while (pred list)

-drop-while (pred list)

-split-at (n list)

-rotate (n list)

-insert-at (n x list)

-split-with (pred list)

-separate (pred list)

-partition (n list)

-partition-all-in-steps (n step list)

-partition-in-steps (n step list)

-partition-all (n list)

-partition-by (fn list)

-partition-by-header (fn list)

-group-by (fn list)

-interpose (sep list)

-interleave (&rest lists)

-zip-with (fn list1 list2)

-zip (list1 list2)

-first (pred list)

-last (pred list)

-first-item (list)

-last-item (list)

-union (list list2)

-difference (list list2)

-intersection (list list2)

-distinct (list)

-contains? (list element)

-sort (predicate list)

-> (x &optional form &rest more)

->> (x form &rest more)

--> (x form &rest more)

-when-let (var-val &rest body)

-when-let* (vars-vals &rest body)

-if-let (var-val then &optional else)

-if-let* (vars-vals then &optional else)

-partial (fn &rest args)

-rpartial (fn &rest args)

-juxt (&rest fns)

-applify (fn)

-on (operator transformer)

-flip (func)

-const (c)