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.

If you want the function combinators, then also:

M-x package-install dash-functional

Using in a package

Add this to the big comment block at the top:

;; Package-Requires: ((dash "2.8.0"))

To get function combinators:

;; Package-Requires: ((dash "2.8.0") (dash-functional "1.1.0") (emacs "24"))

Syntax highlighting of dash functions

Font lock of dash functions in emacs lisp buffers is now optional. Include this in your emacs settings to get syntax highlighting:

(eval-after-load "dash" '(dash-enable-font-lock))

Functions

Maps

Functions in this category take a transforming function, which is then applied sequentially to each or selected elements of the input list. The results are collected in order and returned as new list.

• -map (fn list)
• -map-when (pred rep list)
• -map-indexed (fn list)
• -annotate (fn list)
• -splice (pred fun list)
• -splice-list (pred new-list list)
• -mapcat (fn list)
• -copy (arg)

Sublist selection

Functions returning a sublist of the original list.

• -filter (pred list)
• -remove (pred list)
• -non-nil (list)
• -slice (list from &optional to step)
• -take (n list)
• -drop (n list)
• -take-while (pred list)
• -drop-while (pred list)
• -select-by-indices (indices list)

List to list

Bag of various functions which modify input list.

• -keep (fn list)
• -concat (&rest lists)
• -flatten (l)
• -flatten-n (num list)
• -replace (old new list)
• -insert-at (n x list)
• -replace-at (n x list)
• -update-at (n func list)
• -remove-at (n list)
• -remove-at-indices (indices list)

Reductions

Functions reducing lists into single value.

• -reduce-from (fn initial-value list)
• -reduce-r-from (fn initial-value list)
• -reduce (fn list)
• -reduce-r (fn list)
• -count (pred list)
• -sum (list)
• -product (list)
• -min (list)
• -min-by (comparator list)
• -max (list)
• -max-by (comparator list)

Unfolding

Operations dual to reductions, building lists from seed value rather than consuming a list to produce a single value.

• -iterate (fun init n)
• -unfold (fun seed)

Predicates

• -any? (pred list)
• -all? (pred list)
• -none? (pred list)
• -only-some? (pred list)
• -contains? (list element)
• -same-items? (list list2)
• -is-prefix? (prefix list)
• -is-suffix? (suffix list)
• -is-infix? (infix list)

Partitioning

Functions partitioning the input list into a list of lists.

• -split-at (n list)
• -split-with (pred list)
• -split-on (item list)
• -split-when (fn list)
• -separate (pred list)
• -partition (n list)
• -partition-all (n list)
• -partition-in-steps (n step list)
• -partition-all-in-steps (n step list)
• -partition-by (fn list)
• -partition-by-header (fn list)
• -group-by (fn list)

Indexing

Return indices of elements based on predicates, sort elements by indices etc.

• -elem-index (elem list)
• -elem-indices (elem list)
• -find-index (pred list)
• -find-last-index (pred list)
• -find-indices (pred list)
• -grade-up (comparator list)
• -grade-down (comparator list)

Set operations

Operations pretending lists are sets.

• -union (list list2)
• -difference (list list2)
• -intersection (list list2)
• -distinct (list)

Other list operations

Other list functions not fit to be classified elsewhere.

• -rotate (n list)
• -repeat (n x)
• -cons* (&rest args)
• -snoc (list elem &rest elements)
• -interpose (sep list)
• -interleave (&rest lists)
• -zip-with (fn list1 list2)
• -zip (&rest lists)
• -zip-fill (fill-value &rest lists)
• -cycle (list)
• -pad (fill-value &rest lists)
• -table (fn &rest lists)
• -table-flat (fn &rest lists)
• -first (pred list)
• -last (pred list)
• -first-item (list)
• -last-item (list)
• -butlast (list)
• -sort (comparator list)
• -list (&rest args)
• -fix (fn list)

Tree operations

Functions pretending lists are trees.

• -tree-seq (branch children tree)
• -tree-map (fn tree)
• -tree-map-nodes (pred fun tree)
• -tree-reduce (fn tree)
• -tree-reduce-from (fn init-value tree)
• -tree-mapreduce (fn folder tree)
• -tree-mapreduce-from (fn folder init-value tree)
• -clone (list)

Threading macros

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

Binding

Convenient versions of let and let* constructs combined with flow control.

• -when-let (var-val &rest body)
• -when-let* (vars-vals &rest body)
• -if-let (var-val then &rest else)
• -if-let* (vars-vals then &rest else)

Side-effects

Functions iterating over lists for side-effect only.

• -each (list fn)
• -each-while (list pred fn)
• -dotimes (num fn)

Destructive operations

• !cons (car cdr)
• !cdr (list)

Function combinators

These combinators require Emacs 24 for its lexical scope. So they are offered in a separate package: dash-functional.

• -partial (fn &rest args)
• -rpartial (fn &rest args)
• -juxt (&rest fns)
• -compose (&rest fns)
• -applify (fn)
• -on (operator transformer)
• -flip (func)
• -const (c)
• -cut (&rest params)
• -not (pred)
• -orfn (&rest preds)
• -andfn (&rest preds)
• -iteratefn (fn n)
• -fixfn (fn)
• -prodfn (&rest fns)

Anaphoric functions

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

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.

Maps

Functions in this category take a transforming function, which is then applied sequentially to each or selected elements of the input list. The results are collected in order and returned as new list.

-map (fn list)

Return 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)

-map-when (pred rep list)

Return 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.

Alias: -replace-where

See also: -update-at

(-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)

Return 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)

-annotate (fn list)

Return a list of cons cells where each cell is fn applied to each element of list paired with the unmodified element of list.

(-annotate '1+ '(1 2 3)) ;; => '((2 . 1) (3 . 2) (4 . 3))
(-annotate 'length '(("h" "e" "l" "l" "o") ("hello" "world"))) ;; => '((5 "h" "e" "l" "l" "o") (2 "hello" "world"))
(--annotate (< 1 it) '(0 1 2 3)) ;; => '((nil . 0) (nil . 1) (t . 2) (t . 3))

-splice (pred fun list)

Splice lists generated by fun in place of elements matching pred in list.

fun takes the element matching pred as input.

This function can be used as replacement for ,@ in case you need to splice several lists at marked positions (for example with keywords).

See also: -splice-list, -insert-at

(-splice 'even? (lambda (x) (list x x)) '(1 2 3 4)) ;; => '(1 2 2 3 4 4)
(--splice 't (list it it) '(1 2 3 4)) ;; => '(1 1 2 2 3 3 4 4)
(--splice (equal it :magic) '((list of) (magical) (code)) '((foo) (bar) :magic (baz))) ;; => '((foo) (bar) (list of) (magical) (code) (baz))

-splice-list (pred new-list list)

Splice new-list in place of elements matching pred in list.

See also: -splice, -insert-at

(-splice-list 'keywordp '(a b c) '(1 :foo 2)) ;; => '(1 a b c 2)
(-splice-list 'keywordp nil '(1 :foo 2)) ;; => '(1 2)

-mapcat (fn list)

Return 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)

-copy (arg)

Create a shallow copy of list.

(-copy '(1 2 3)) ;; => '(1 2 3)
(let ((a '(1 2 3))) (eq a (-copy a))) ;; => nil

Sublist selection

Functions returning a sublist of the original list.

-filter (pred list)

Return 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)

Return 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)

-non-nil (list)

Return all non-nil elements of list.

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

-slice (list from &optional to step)

Return copy of list, starting from index from to index to.

from or to may be negative. These values are then interpreted modulo the length of the list.

If step is a number, only each STEPth item in the resulting section is returned. Defaults to 1.

(-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 6 7 8 9) 1 -1 2) ;; => '(2 4 6 8)

-take (n list)

Return 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)

Return 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)

Return 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)

Return 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)

-select-by-indices (indices list)

Return a list whose elements are elements from list selected as (nth i list) for all i from indices.

(-select-by-indices '(4 10 2 3 6) '("v" "e" "l" "o" "c" "i" "r" "a" "p" "t" "o" "r")) ;; => '("c" "o" "l" "o" "r")
(-select-by-indices '(2 1 0) '("a" "b" "c")) ;; => '("c" "b" "a")
(-select-by-indices '(0 1 2 0 1 3 3 1) '("f" "a" "r" "l")) ;; => '("f" "a" "r" "f" "a" "l" "l" "a")

List to list

Bag of various functions which modify input list.

-keep (fn list)

Return 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)

-concat (&rest lists)

Return 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)

-flatten (l)

Take a nested list l and return its contents as a single, flat list.

See also: -flatten-n

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

-flatten-n (num list)

Flatten num levels of a nested list.

See also: -flatten

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

-replace (old new list)

Replace all old items in list with new.

Elements are compared using equal.

See also: -replace-at

(-replace 1 "1" '(1 2 3 4 3 2 1)) ;; => '("1" 2 3 4 3 2 "1")
(-replace "foo" "bar" '("a" "nice" "foo" "sentence" "about" "foo")) ;; => '("a" "nice" "bar" "sentence" "about" "bar")
(-replace 1 2 nil) ;; => nil

-insert-at (n x list)

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

See also: -splice, -splice-list

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

-replace-at (n x list)

Return a list with element at Nth position in list replaced with x.

See also: -replace

(-replace-at 0 9 '(0 1 2 3 4 5)) ;; => '(9 1 2 3 4 5)
(-replace-at 1 9 '(0 1 2 3 4 5)) ;; => '(0 9 2 3 4 5)
(-replace-at 4 9 '(0 1 2 3 4 5)) ;; => '(0 1 2 3 9 5)

-update-at (n func list)

Return a list with element at Nth position in list replaced with (func (nth n list)).

See also: -map-when

(-update-at 0 (lambda (x) (+ x 9)) '(0 1 2 3 4 5)) ;; => '(9 1 2 3 4 5)
(-update-at 1 (lambda (x) (+ x 8)) '(0 1 2 3 4 5)) ;; => '(0 9 2 3 4 5)
(--update-at 2 (length it) '("foo" "bar" "baz" "quux")) ;; => '("foo" "bar" 3 "quux")

-remove-at (n list)

Return a list with element at Nth position in list removed.

See also: -remove-at-indices, -remove

(-remove-at 0 '("0" "1" "2" "3" "4" "5")) ;; => '("1" "2" "3" "4" "5")
(-remove-at 1 '("0" "1" "2" "3" "4" "5")) ;; => '("0" "2" "3" "4" "5")
(-remove-at 2 '("0" "1" "2" "3" "4" "5")) ;; => '("0" "1" "3" "4" "5")

-remove-at-indices (indices list)

Return a list whose elements are elements from list without elements selected as (nth i list) for all i from indices.

See also: -remove-at, -remove

(-remove-at-indices '(0) '("0" "1" "2" "3" "4" "5")) ;; => '("1" "2" "3" "4" "5")
(-remove-at-indices '(0 2 4) '("0" "1" "2" "3" "4" "5")) ;; => '("1" "3" "5")
(-remove-at-indices '(0 5) '("0" "1" "2" "3" "4" "5")) ;; => '("1" "2" "3" "4")

Reductions

Functions reducing lists into single value.

-reduce-from (fn initial-value list)

Return 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, return 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)

Return 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 return 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 return 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"

-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 4)) ;; => 10

-product (list)

Return the product of list.

(-product '()) ;; => 1
(-product '(1)) ;; => 1
(-product '(1 2 3 4)) ;; => 24

-min (list)

Return the smallest value from list of numbers or markers.

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

-min-by (comparator list)

Take a comparison function comparator and a list and return the least element of the list by the comparison function.

See also combinator -on which can transform the values before comparing them.

(-min-by '> '(4 3 6 1)) ;; => 1
(--min-by (> (car it) (car other)) '((1 2 3) (2) (3 2))) ;; => '(1 2 3)
(--min-by (> (length it) (length other)) '((1 2 3) (2) (3 2))) ;; => '(2)

-max (list)

Return the largest value from list of numbers or markers.

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

-max-by (comparator list)

Take a comparison function comparator and a list and return the greatest element of the list by the comparison function.

See also combinator -on which can transform the values before comparing them.

(-max-by '> '(4 3 6 1)) ;; => 6
(--max-by (> (car it) (car other)) '((1 2 3) (2) (3 2))) ;; => '(3 2)
(--max-by (> (length it) (length other)) '((1 2 3) (2) (3 2))) ;; => '(1 2 3)

Unfolding

Operations dual to reductions, building lists from seed value rather than consuming a list to produce a single value.

-iterate (fun init n)

Return a list of iterated applications of fun to init.

This means a list of form:

(init (fun init) (fun (fun init)) ...)

n is the length of the returned list.

(-iterate '1+ 1 10) ;; => '(1 2 3 4 5 6 7 8 9 10)
(-iterate (lambda (x) (+ x x)) 2 5) ;; => '(2 4 8 16 32)
(--iterate (* it it) 2 5) ;; => '(2 4 16 256 65536)

-unfold (fun seed)

Build a list from seed using fun.

This is "dual" operation to -reduce-r: while -reduce-r consumes a list to produce a single value, -unfold takes a seed value and builds a (potentially infinite!) list.

fun should return nil to stop the generating process, or a cons (a . b), where a will be prepended to the result and b is the new seed.

(-unfold (lambda (x) (unless (= x 0) (cons x (1- x)))) 10) ;; => '(10 9 8 7 6 5 4 3 2 1)
(--unfold (when it (cons it (cdr it))) '(1 2 3 4)) ;; => '((1 2 3 4) (2 3 4) (3 4) (4))
(--unfold (when it (cons it (butlast it))) '(1 2 3 4)) ;; => '((1 2 3 4) (1 2 3) (1 2) (1))

Predicates

-any? (pred list)

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

Alias: -any-p, -some?, -some-p

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

-all? (pred list)

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

Alias: -all-p, -every?, -every-p

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

-none? (pred list)

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

Alias: -none-p

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

-only-some? (pred list)

Return t if at least one item of list matches pred and at least one item of list does not match pred. Return nil both if all items match the predicate or if none of the items match the predicate.

Alias: -only-some-p

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

-contains? (list element)

Return non-nil if list contains element.

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

Alias: -contains-p

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

-same-items? (list list2)

Return true if list and list2 has the same items.

The order of the elements in the lists does not matter.

Alias: -same-items-p

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

-is-prefix? (prefix list)

Return non-nil if prefix is prefix of list.

Alias: -is-prefix-p

(-is-prefix? '(1 2 3) '(1 2 3 4 5)) ;; => t
(-is-prefix? '(1 2 3 4 5) '(1 2 3)) ;; => nil
(-is-prefix? '(1 3) '(1 2 3 4 5)) ;; => nil

-is-suffix? (suffix list)

Return non-nil if suffix is suffix of list.

Alias: -is-suffix-p

(-is-suffix? '(3 4 5) '(1 2 3 4 5)) ;; => t
(-is-suffix? '(1 2 3 4 5) '(3 4 5)) ;; => nil
(-is-suffix? '(3 5) '(1 2 3 4 5)) ;; => nil

-is-infix? (infix list)

Return non-nil if infix is infix of list.

This operation runs in o(n^2) time

Alias: -is-infix-p

(-is-infix? '(1 2 3) '(1 2 3 4 5)) ;; => t
(-is-infix? '(2 3 4) '(1 2 3 4 5)) ;; => t
(-is-infix? '(3 4 5) '(1 2 3 4 5)) ;; => t

Partitioning

Functions partitioning the input list into a list of lists.

-split-at (n list)

Return 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)

-split-with (pred list)

Return 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))

-split-on (item list)

Split the list each time item is found.

Unlike -partition-by, the item is discarded from the results. Empty lists are also removed from the result.

Comparison is done by equal.

See also -split-when

(-split-on '| '(Nil | Leaf a | Node [Tree a])) ;; => '((Nil) (Leaf a) (Node [Tree a]))
(-split-on ':endgroup '("a" "b" :endgroup "c" :endgroup "d" "e")) ;; => '(("a" "b") ("c") ("d" "e"))
(-split-on ':endgroup '("a" "b" :endgroup :endgroup "d" "e")) ;; => '(("a" "b") ("d" "e"))

-split-when (fn list)

Split the list on each element where fn returns non-nil.

Unlike -partition-by, the "matched" element is discarded from the results. Empty lists are also removed from the result.

This function can be thought of as a generalization of split-string.

(-split-when 'even? '(1 2 3 4 5 6)) ;; => '((1) (3) (5))
(-split-when 'even? '(1 2 3 4 6 8 9)) ;; => '((1) (3) (9))
(--split-when (memq it '(&optional &rest)) '(a b &optional c d &rest args)) ;; => '((a b) (c d) (args))

-separate (pred list)

Return 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)

Return 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 (n list)

Return 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-in-steps (n step list)

Return 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-in-steps (n step list)

Return 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-by (fn list)

Apply 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)

Apply fn to the first item in list. That is the header value. Apply 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"))

Indexing

Return indices of elements based on predicates, sort elements by indices etc.

-elem-index (elem list)

Return the index of the first element in the given list which is equal to the query element elem, or nil if there is no such element.

(-elem-index 2 '(6 7 8 2 3 4)) ;; => 3
(-elem-index "bar" '("foo" "bar" "baz")) ;; => 1
(-elem-index '(1 2) '((3) (5 6) (1 2) nil)) ;; => 2

-elem-indices (elem list)

Return the indices of all elements in list equal to the query element elem, in ascending order.

(-elem-indices 2 '(6 7 8 2 3 4 2 1)) ;; => '(3 6)
(-elem-indices "bar" '("foo" "bar" "baz")) ;; => '(1)
(-elem-indices '(1 2) '((3) (1 2) (5 6) (1 2) nil)) ;; => '(1 3)

-find-index (pred list)

Take a predicate pred and a list and return the index of the first element in the list satisfying the predicate, or nil if there is no such element.

(-find-index 'even? '(2 4 1 6 3 3 5 8)) ;; => 0
(--find-index (< 5 it) '(2 4 1 6 3 3 5 8)) ;; => 3
(-find-index (-partial 'string-lessp "baz") '("bar" "foo" "baz")) ;; => 1

-find-last-index (pred list)

Take a predicate pred and a list and return the index of the last element in the list satisfying the predicate, or nil if there is no such element.

(-find-last-index 'even? '(2 4 1 6 3 3 5 8)) ;; => 7
(--find-last-index (< 5 it) '(2 7 1 6 3 8 5 2)) ;; => 5
(-find-last-index (-partial 'string-lessp "baz") '("q" "foo" "baz")) ;; => 1

-find-indices (pred list)

Return the indices of all elements in list satisfying the predicate pred, in ascending order.

(-find-indices 'even? '(2 4 1 6 3 3 5 8)) ;; => '(0 1 3 7)
(--find-indices (< 5 it) '(2 4 1 6 3 3 5 8)) ;; => '(3 7)
(-find-indices (-partial 'string-lessp "baz") '("bar" "foo" "baz")) ;; => '(1)

-grade-up (comparator list)

Grade elements of list using comparator relation, yielding a permutation vector such that applying this permutation to list sorts it in ascending order.

(-grade-up '< '(3 1 4 2 1 3 3)) ;; => '(1 4 3 0 5 6 2)
(let ((l '(3 1 4 2 1 3 3))) (-select-by-indices (-grade-up '< l) l)) ;; => '(1 1 2 3 3 3 4)

-grade-down (comparator list)

Grade elements of list using comparator relation, yielding a permutation vector such that applying this permutation to list sorts it in descending order.

(-grade-down '< '(3 1 4 2 1 3 3)) ;; => '(2 0 5 6 3 1 4)
(let ((l '(3 1 4 2 1 3 3))) (-select-by-indices (-grade-down '< l) l)) ;; => '(4 3 3 3 2 1 1)

Set operations

Operations pretending lists are sets.

-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)

Other list operations

Other list functions not fit to be classified elsewhere.

-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)

-repeat (n x)

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

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

-cons* (&rest args)

Make 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

-snoc (list elem &rest elements)

Append elem to the end of the list.

This is like cons, but operates on the end of list.

If elements is non nil, append these to the list as well.

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

-interpose (sep list)

Return 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)

Return 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 (&rest lists)

Zip lists together. Group the head of each list, followed by the second elements of each list, and so on. The lengths of the returned groupings are equal to the length of the shortest input list.

If two lists are provided as arguments, return the groupings as a list of cons cells. Otherwise, return the groupings as a list of lists.

(-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))

-zip-fill (fill-value &rest lists)

Zip lists, with fill-value padded onto the shorter lists. The lengths of the returned groupings are equal to the length of the longest input list.

(-zip-fill 0 '(1 2 3 4 5) '(6 7 8 9)) ;; => '((1 . 6) (2 . 7) (3 . 8) (4 . 9) (5 . 0))

-cycle (list)

Return an infinite copy of list that will cycle through the elements and repeat from the beginning.

(-take 5 (-cycle '(1 2 3))) ;; => '(1 2 3 1 2)
(-take 7 (-cycle '(1 "and" 3))) ;; => '(1 "and" 3 1 "and" 3 1)
(-zip (-cycle '(1 2 3)) '(1 2)) ;; => '((1 . 1) (2 . 2))

-pad (fill-value &rest lists)

Appends fill-value to the end of each list in lists such that they will all have the same length.

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

-table (fn &rest lists)

Compute outer product of lists using function fn.

The function fn should have the same arity as the number of supplied lists.

The outer product is computed by applying fn to all possible combinations created by taking one element from each list in order. The dimension of the result is (length lists).

See also: -table-flat

(-table '* '(1 2 3) '(1 2 3)) ;; => '((1 2 3) (2 4 6) (3 6 9))
(-table (lambda (a b) (-sum (-zip-with '* a b))) '((1 2) (3 4)) '((1 3) (2 4))) ;; => '((7 15) (10 22))
(apply '-table 'list (-repeat 3 '(1 2))) ;; => '((((1 1 1) (2 1 1)) ((1 2 1) (2 2 1))) (((1 1 2) (2 1 2)) ((1 2 2) (2 2 2))))

-table-flat (fn &rest lists)

Compute flat outer product of lists using function fn.

The function fn should have the same arity as the number of supplied lists.

The outer product is computed by applying fn to all possible combinations created by taking one element from each list in order. The results are flattened, ignoring the tensor structure of the result. This is equivalent to calling:

(-flatten-n (1- (length lists)) (-table fn lists))

but the implementation here is much more efficient.

See also: -flatten-n, -table

(-table-flat 'list '(1 2 3) '(a b c)) ;; => '((1 a) (2 a) (3 a) (1 b) (2 b) (3 b) (1 c) (2 c) (3 c))
(-table-flat '* '(1 2 3) '(1 2 3)) ;; => '(1 2 3 2 4 6 3 6 9)
(apply '-table-flat 'list (-repeat 3 '(1 2))) ;; => '((1 1 1) (2 1 1) (1 2 1) (2 2 1) (1 1 2) (2 1 2) (1 2 2) (2 2 2))

-first (pred list)

Return 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.

Alias: -find

(-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)

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

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

-last-item (list)

Return the last item of list, or nil on an empty list.

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

-butlast (list)

Return a list of all items in list except for the last.

(-butlast '(1 2 3)) ;; => '(1 2)
(-butlast '(1 2)) ;; => '(1)
(-butlast '(1)) ;; => nil

-sort (comparator list)

Sort list, stably, comparing elements using comparator. Return the sorted list. list is not modified by side effects. comparator 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)

-list (&rest args)

Return a list with args.

If first item of args is already a list, simply return args. If not, return a list with args as elements.

(-list 1) ;; => '(1)
(-list 1 2 3) ;; => '(1 2 3)

-fix (fn list)

Compute the (least) fixpoint of fn with initial input list.

fn is called at least once, results are compared with equal.

(-fix (lambda (l) (-non-nil (--mapcat (-split-at (/ (length it) 2) it) l))) '((1 2 3 4 5 6))) ;; => '((1) (2) (3) (4) (5) (6))
(let ((data '(("starwars" "scifi") ("jedi" "starwars" "warrior")))) (--fix (-uniq (--mapcat (cons it (cdr (assoc it data))) it)) '("jedi" "book"))) ;; => '("jedi" "starwars" "warrior" "scifi" "book")

Tree operations

Functions pretending lists are trees.

-tree-seq (branch children tree)

Return a sequence of the nodes in tree, in depth-first search order.

branch is a predicate of one argument that returns non-nil if the passed argument is a branch, that is, a node that can have children.

children is a function of one argument that returns the children of the passed branch node.

Non-branch nodes are simply copied.

(-tree-seq 'listp 'identity '(1 (2 3) 4 (5 (6 7)))) ;; => '((1 (2 3) 4 (5 (6 7))) 1 (2 3) 2 3 4 (5 (6 7)) 5 (6 7) 6 7)
(-tree-seq 'listp 'reverse '(1 (2 3) 4 (5 (6 7)))) ;; => '((1 (2 3) 4 (5 (6 7))) (5 (6 7)) (6 7) 7 6 5 4 (2 3) 3 2 1)
(--tree-seq (vectorp it) (append it nil) [1 [2 3] 4 [5 [6 7]]]) ;; => '([1 [2 3] 4 [5 [6 7]]] 1 [2 3] 2 3 4 [5 [6 7]] 5 [6 7] 6 7)

-tree-map (fn tree)

Apply fn to each element of tree while preserving the tree structure.

(-tree-map '1+ '(1 (2 3) (4 (5 6) 7))) ;; => '(2 (3 4) (5 (6 7) 8))
(-tree-map '(lambda (x) (cons x (expt 2 x))) '(1 (2 3) 4)) ;; => '((1 . 2) ((2 . 4) (3 . 8)) (4 . 16))
(--tree-map (length it) '("<body>" ("<p>" "text" "</p>") "</body>")) ;; => '(6 (3 4 4) 7)

-tree-map-nodes (pred fun tree)

Call fun on each node of tree that satisfies pred.

If pred returns nil, continue descending down this node. If pred returns non-nil, apply fun to this node and do not descend further.

(-tree-map-nodes 'vectorp (lambda (x) (-sum (append x nil))) '(1 [2 3] 4 (5 [6 7] 8))) ;; => '(1 5 4 (5 13 8))
(-tree-map-nodes 'keywordp (lambda (x) (symbol-name x)) '(1 :foo 4 ((5 6 :bar) :baz 8))) ;; => '(1 ":foo" 4 ((5 6 ":bar") ":baz" 8))
(--tree-map-nodes (eq (car-safe it) 'add-mode) (-concat it (list :mode 'emacs-lisp-mode)) '(with-mode emacs-lisp-mode (foo bar) (add-mode a b) (baz (add-mode c d)))) ;; => '(with-mode emacs-lisp-mode (foo bar) (add-mode a b :mode emacs-lisp-mode) (baz (add-mode c d :mode emacs-lisp-mode)))

-tree-reduce (fn tree)

Use fn to reduce elements of list tree. If elements of tree are lists themselves, apply the reduction recursively.

fn is first applied to first element of the list and second element, then on this result and third element from the list etc.

See -reduce-r for how exactly are lists of zero or one element handled.

(-tree-reduce '+ '(1 (2 3) (4 5))) ;; => 15
(-tree-reduce 'concat '("strings" (" on" " various") ((" levels")))) ;; => "strings on various levels"
(--tree-reduce (cond ((stringp it) (concat it " " acc)) (t (let ((sn (symbol-name it))) (concat "<" sn ">" acc "</" sn ">")))) '(body (p "some words") (div "more" (b "bold") "words"))) ;; => "<body><p>some words</p> <div>more <b>bold</b> words</div></body>"

-tree-reduce-from (fn init-value tree)

Use fn to reduce elements of list tree. If elements of tree are lists themselves, apply the reduction recursively.

fn is first applied to init-value and first element of the list, then on this result and second element from the list etc.

The initial value is ignored on cons pairs as they always contain two elements.

(-tree-reduce-from '+ 1 '(1 (1 1) ((1)))) ;; => 8
(--tree-reduce-from (-concat acc (list it)) nil '(1 (2 3 (4 5)) (6 7))) ;; => '((7 6) ((5 4) 3 2) 1)

-tree-mapreduce (fn folder tree)

Apply fn to each element of tree, and make a list of the results. If elements of tree are lists themselves, apply fn recursively to elements of these nested lists.

Then reduce the resulting lists using folder and initial value init-value. See -reduce-r-from.

This is the same as calling -tree-reduce after -tree-map but is twice as fast as it only traverse the structure once.

(-tree-mapreduce 'list 'append '(1 (2 (3 4) (5 6)) (7 (8 9)))) ;; => '(1 2 3 4 5 6 7 8 9)
(--tree-mapreduce 1 (+ it acc) '(1 (2 (4 9) (2 1)) (7 (4 3)))) ;; => 9
(--tree-mapreduce 0 (max acc (1+ it)) '(1 (2 (4 9) (2 1)) (7 (4 3)))) ;; => 3

-tree-mapreduce-from (fn folder init-value tree)

Apply fn to each element of tree, and make a list of the results. If elements of tree are lists themselves, apply fn recursively to elements of these nested lists.

Then reduce the resulting lists using folder and initial value init-value. See -reduce-r-from.

This is the same as calling -tree-reduce-from after -tree-map but is twice as fast as it only traverse the structure once.

(-tree-mapreduce-from 'identity '* 1 '(1 (2 (3 4) (5 6)) (7 (8 9)))) ;; => 362880
(--tree-mapreduce-from (+ it it) (cons it acc) nil '(1 (2 (4 9) (2 1)) (7 (4 3)))) ;; => '(2 (4 (8 18) (4 2)) (14 (8 6)))
(concat "{" (--tree-mapreduce-from (cond ((-cons-pair? it) (concat (symbol-name (car it)) " -> " (symbol-name (cdr it)))) (t (concat (symbol-name it) " : {"))) (concat it (unless (or (equal acc "}") (equal (substring it (1- (length it))) "{")) ", ") acc) "}" '((elips-mode (foo (bar . booze)) (baz . qux)) (c-mode (foo . bla) (bum . bam))))) ;; => "{elips-mode : {foo : {bar -> booze}, baz -> qux}, c-mode : {foo -> bla, bum -> bam}}"

-clone (list)

Create a deep copy of list. The new list has the same elements and structure but all cons are replaced with new ones. This is useful when you need to clone a structure such as plist or alist.

(let* ((a '(1 2 3)) (b (-clone a))) (nreverse a) b) ;; => '(1 2 3)

Threading macros

-> (x &optional form &rest more)

Thread the expr through the forms. Insert 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, insert the first form as the second item in second form, etc.

(-> '(2 3 5)) ;; => '(2 3 5)
(-> '(2 3 5) (append '(8 13))) ;; => '(2 3 5 8 13)
(-> '(2 3 5) (append '(8 13)) (-slice 1 -1)) ;; => '(3 5 8)

->> (x form &rest more)

Thread the expr through the forms. Insert 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, insert the first form as the last item in second form, etc.

(->> '(1 2 3) (-map 'square)) ;; => '(1 4 9)
(->> '(1 2 3) (-map 'square) (-remove 'even?)) ;; => '(1 9)
(->> '(1 2 3) (-map 'square) (-reduce '+)) ;; => 14

--> (x form &rest more)

Thread the expr through the forms. Insert x at the position signified by the token it in the first form. If there are more forms, insert 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"

Binding

Convenient versions of let and let* constructs combined with flow control.

-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 &rest 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 &rest 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"

Side-effects

Functions iterating over lists for side-effect only.

-each (list fn)

Call fn with every item in list. Return 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)

Call fn with every item in list while (pred item) is non-nil. Return 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 num-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)

Destructive operations

!cons (car cdr)

Destructive: Set 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: Set list to the cdr of list.

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

Function combinators

These combinators require Emacs 24 for its lexical scope. So they are offered in a separate package: dash-functional.

-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)

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 the additional args first and then args.

(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).

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

-compose (&rest fns)

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

(funcall (-compose 'square '+) 2 3) ;; => (square (+ 2 3))
(funcall (-compose 'identity 'square) 3) ;; => (square 3)
(funcall (-compose 'square 'identity) 3) ;; => (square 3)

-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))
(-min-by (-on '> 'length) '((1 2 3) (4) (1 2))) ;; => '(4)
(-min-by (-on 'string-lessp 'int-to-string) '(2 100 22)) ;; => 22

-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)

-iteratefn (fn n)

Return a function fn composed n times with itself.

fn is a unary function. If you need to use a function of higher arity, use -applify first to turn it into an unary function.

With n = 0, this acts as identity function.

In types: (a -> a) -> Int -> a -> a.

This function satisfies the following law:

(funcall (-iteratefn fn n) init) = (-last-item (-iterate fn init (1+ n))).

(funcall (-iteratefn (lambda (x) (* x x)) 3) 2) ;; => 256
(funcall (-iteratefn '1+ 3) 1) ;; => 4
(funcall (-iteratefn 'cdr 3) '(1 2 3 4 5)) ;; => '(4 5)

-fixfn (fn)

Return a function that computes the (least) fixpoint of fn.

fn is a unary function, results are compared with equal.

In types: (a -> a) -> a -> a.

(funcall (-fixfn 'cos) 0.7) ;; => 0.7390851332151607
(funcall (-fixfn (lambda (x) (expt (+ x 10) 0.25))) 2.0) ;; => 1.8555845286409378

-prodfn (&rest fns)

Take a list of n functions and return a function that takes a list of length n, applying i-th function to i-th element of the input list. Returns a list of length n.

In types (for n=2): ((a -> b), (c -> d)) -> (a, c) -> (b, d)

This function satisfies the following laws:

(-compose (-prodfn f g ...) (-prodfn f' g' ...)) = (-prodfn (-compose f f') (-compose g g') ...)
(-prodfn f g ...) = (-juxt (-compose f (-partial 'nth 0)) (-compose g (-partial 'nth 1)) ...)
(-compose (-prodfn f g ...) (-juxt f' g' ...)) = (-juxt (-compose f f') (-compose g g') ...)
(-compose (-partial 'nth n) (-prod f1 f2 ...)) = (-compose fn (-partial 'nth n))

(funcall (-prodfn '1+ '1- 'int-to-string) '(1 2 3)) ;; => '(2 1 "3")
(-map (-prodfn '1+ '1-) '((1 2) (3 4) (5 6) (7 8))) ;; => '((2 1) (4 3) (6 5) (8 7))
(apply '+ (funcall (-prodfn 'length 'string-to-int) '((1 2 3) "15"))) ;; => 18

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 2.7 to 2.8

• Add -butlast

From 2.6 to 2.7

• -zip now supports more than two lists (Steve Lamb)
• Add -cycle , -pad , -annotate , -zip-fill (Steve Lamb)
• Add -table, -table-flat (finite cartesian product)
• Add -flatten-n
• -slice now supports "step" argument
• Add functional combinators -iteratefn, -prodfn
• Add -replace, -splice, -splice-list which generalize -replace-at and -insert-at
• Add -compose, -iteratefn and -prodfn (dash-functional 1.1)

From 2.5 to 2.6

• Add -is-prefix-p, -is-suffix-p, -is-infix-p (Matus Goljer)
• Add -iterate, -unfold (Matus Goljer)
• Add -split-on, -split-when (Matus Goljer)
• Add -find-last-index (Matus Goljer)
• Add -list (Johan Andersson)

From 2.4 to 2.5

• Add -same-items? (Johan Andersson)
• A few bugfixes

From 2.3 to 2.4

• Add -snoc (Matus Goljer)
• Add -replace-at, -update-at, -remove-at, and -remove-at-indices (Matus Goljer)

From 2.2 to 2.3

• Add tree operations (Matus Goljer)
• Make font-lock optional

From 2.1 to 2.2

• Add -compose (Christina Whyte)

From 2.0 to 2.1

• Add indexing operations (Matus Goljer)

From 1.8 to 2.0

• Split out dash-functional.el (Matus Goljer)
• Add -andfn, -orfn, -not, -cut, -const, -flip and -on. (Matus Goljer)
• Fix -min, -max, -min-by and -max-by (Matus Goljer)

From 1.7 to 1.8

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

From 1.6 to 1.7

• Add -rotate (Matus Goljer)

From 1.5 to 1.6

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

From 1.4 to 1.5

• Add -sum and -product (Johan Andersson)

From 1.3 to 1.4

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

From 1.2 to 1.3

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

From 1.1 to 1.2

• 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 lots of features and functions.
• 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 and -same-items?
• Christina Whyte contributed -compose
• Steve Lamb contributed -cycle, -pad, -annotate, -zip-fill and an n-ary version of -zip.

Thanks!

License

Copyright (C) 2012-2013 Magnar Sveen

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/.