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

See the end of the file for license conditions.

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See the NEWS.md file.

Dash is available on GNU ELPA, GNU-devel ELPA, and MELPA, and can be installed with the standard command package-install:

M-x package-install RET dash RET

See (info "(emacs) Package Installation").

Alternatively, you can just dump dash.el in your load-path somewhere. See (info "(emacs) Lisp Libraries").

Add something like this to the library's headers:

;; Package-Requires: ((dash "2.19.1"))

See (info "(elisp) Library Headers").

Font lock of special Dash variables (it, acc, etc.) in Emacs Lisp buffers can optionally be enabled with the autoloaded minor mode dash-fontify-mode. In older Emacs versions which do not dynamically detect macros, the minor mode also fontifies Dash macro calls.

To automatically enable the minor mode in all Emacs Lisp buffers, just call its autoloaded global counterpart global-dash-fontify-mode, either interactively or from your user-init-file:

(global-dash-fontify-mode)

While editing Elisp files, you can use C-h S (info-lookup-symbol) to look up Elisp symbols in the relevant Info manuals (see (emacs) Info Lookup). To enable the same for Dash symbols, use the command dash-register-info-lookup. It can be called directly when needed, or automatically from your user-init-file. For example:

(with-eval-after-load 'info-look
  (dash-register-info-lookup))

All functions and constructs in the library use a dash (-) prefix.

The library also provides anaphoric macro versions of functions where that makes sense. The names of these macros are prefixed with two dashes (--) instead of one.

While -map applies a function to each element of a list, its anaphoric counterpart --map evaluates a form with the local variable it temporarily bound to the current list element instead. For example:

(-map (lambda (n) (* n n)) '(1 2 3 4)) ; Normal version.
(--map (* it it) '(1 2 3 4))           ; Anaphoric version.

The normal version can of course also be written as follows:

(defun my-square (n)
  "Return N multiplied by itself."
  (* n n))

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

This demonstrates the utility of both versions.

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 a new list.

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

Functions returning a sublist of the original list.

• -filter (pred list)
• -remove (pred list)
• -remove-first (pred list)
• -remove-last (pred list)
• -remove-item (item list)
• -non-nil (list)
• -slice (list from &optional to step)
• -take (n list)
• -take-last (n list)
• -drop (n list)
• -drop-last (n list)
• -take-while (pred list)
• -drop-while (pred list)
• -select-by-indices (indices list)
• -select-columns (columns table)
• -select-column (column table)

Functions returning a modified copy of the input list.

• -keep (fn list)
• -concat (&rest sequences)
• -flatten (l)
• -flatten-n (num list)
• -replace (old new list)
• -replace-first (old new list)
• -replace-last (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)

Functions reducing lists to a single value (which may also be a list).

• -reduce-from (fn init list)
• -reduce-r-from (fn init list)
• -reduce (fn list)
• -reduce-r (fn list)
• -reductions-from (fn init list)
• -reductions-r-from (fn init list)
• -reductions (fn list)
• -reductions-r (fn list)
• -count (pred list)
• -sum (list)
• -running-sum (list)
• -product (list)
• -running-product (list)
• -inits (list)
• -tails (list)
• -common-prefix (&rest lists)
• -common-suffix (&rest lists)
• -min (list)
• -min-by (comparator list)
• -max (list)
• -max-by (comparator list)
• -frequencies (list)

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

• -iterate (fun init n)
• -unfold (fun seed)
• -repeat (n x)
• -cycle (list)

Reductions of one or more lists to a boolean value.

• -some (pred list)
• -every (pred list)
• -any? (pred list)
• -all? (pred list)
• -none? (pred list)
• -only-some? (pred list)
• -contains? (list element)
• -is-prefix? (prefix list)
• -is-suffix? (suffix list)
• -is-infix? (infix list)
• -cons-pair? (obj)

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)
• -partition-after-pred (pred list)
• -partition-before-pred (pred list)
• -partition-before-item (item list)
• -partition-after-item (item list)
• -group-by (fn list)

Functions retrieving or sorting based on list indices and related predicates.

• -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)

Operations pretending lists are sets.

• -union (list1 list2)
• -difference (list1 list2)
• -intersection (list1 list2)
• -powerset (list)
• -permutations (list)
• -distinct (list)
• -same-items? (list1 list2)

Other list functions not fit to be classified elsewhere.

• -rotate (n list)
• -cons* (&rest args)
• -snoc (list elem &rest elements)
• -interpose (sep list)
• -interleave (&rest lists)
• -iota (count &optional start step)
• -zip-with (fn list1 list2)
• -zip-pair (list1 list2)
• -zip-lists (&rest lists)
• -zip-lists-fill (fill-value &rest lists)
• -zip (&rest lists)
• -zip-fill (fill-value &rest lists)
• -unzip-lists (lists)
• -unzip (lists)
• -pad (fill-value &rest lists)
• -table (fn &rest lists)
• -table-flat (fn &rest lists)
• -first (pred list)
• -last (pred list)
• -first-item (list)
• -second-item (list)
• -third-item (list)
• -fourth-item (list)
• -fifth-item (list)
• -last-item (list)
• -butlast (list)
• -sort (comparator list)
• -list (arg)
• -fix (fn list)

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)

Macros that conditionally combine sequential forms for brevity or readability.

• -> (x &optional form &rest more)
• ->> (x &optional form &rest more)
• --> (x &rest forms)
• -as-> (value variable &rest forms)
• -some-> (x &optional form &rest more)
• -some->> (x &optional form &rest more)
• -some--> (expr &rest forms)
• -doto (init &rest forms)

Macros that combine let and let* with destructuring and 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)
• -let (varlist &rest body)
• -let* (varlist &rest body)
• -lambda (match-form &rest body)
• -setq ([match-form val] ...)

Functions iterating over lists for side effect only.

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

Macros that modify variables holding lists.

• !cons (car cdr)
• !cdr (list)

Functions that manipulate and compose other functions.

• -partial (fun &rest args)
• -rpartial (fn &rest args)
• -juxt (&rest fns)
• -compose (&rest fns)
• -applify (fn)
• -on (op trans)
• -flip (fn)
• -rotate-args (n fn)
• -const (c)
• -cut (&rest params)
• -not (pred)
• -orfn (&rest preds)
• -andfn (&rest preds)
• -iteratefn (fn n)
• -fixfn (fn &optional equal-test halt-test)
• -prodfn (&rest fns)

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 a new list.

Apply fn to each item in list and return the list of results.

This function's anaphoric counterpart is --map.

(-map (lambda (num) (* num num)) '(1 2 3 4)) ;; => (1 4 9 16)
(-map #'1+ '(1 2 3 4)) ;; => (2 3 4 5)
(--map (* it it) '(1 2 3 4)) ;; => (1 4 9 16)

Use pred to conditionally apply rep to each item in list. Return a copy of list where the items for which pred returns nil are unchanged, and the rest 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)

Use pred to determine the first item in list to call rep on. Return a copy of list where the first item for which pred returns non-nil is replaced with the result of calling rep on that item.

See also: -map-when, -replace-first

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

Use pred to determine the last item in list to call rep on. Return a copy of list where the last item for which pred returns non-nil is replaced with the result of calling rep on that item.

See also: -map-when, -replace-last

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

Apply fn to each index and item in list and return the list of results. This is like -map, but fn takes two arguments: the index of the current element within list, and the element itself.

This function's anaphoric counterpart is --map-indexed.

For a side-effecting variant, see also -each-indexed.

(-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)
(-map-indexed #'* '(1 2 3 4)) ;; => (0 2 6 12)

Pair each item in list with the result of passing it to fn.

Return an alist of (result . item), where each item is the corresponding element of list, and result is the value obtained by calling fn on item.

This function's anaphoric counterpart is --annotate.

(-annotate #'1+ '(1 2 3)) ;; => ((2 . 1) (3 . 2) (4 . 3))
(-annotate #'length '((f o o) (bar baz))) ;; => ((3 f o o) (2 bar baz))
(--annotate (> it 1) '(0 1 2 3)) ;; => ((nil . 0) (nil . 1) (t . 2) (t . 3))

Splice lists generated by fun in place of items satisfying pred in list.

Call pred on each element of list. Whenever the result of pred is nil, leave that it as-is. Otherwise, call fun on the same it that satisfied pred. The result should be a (possibly empty) list of items to splice in place of it in list.

This can be useful as an alternative to the ,@ construct in a ``' structure, in case you need to splice several lists at marked positions (for example with keywords).

This function's anaphoric counterpart is --splice.

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

(-splice #'numberp (lambda (n) (list n n)) '(a 1 b 2)) ;; => (a 1 1 b 2 2)
(--splice t (list it it) '(1 2 3 4)) ;; => (1 1 2 2 3 3 4 4)
(--splice (eq it :magic) '((magical) (code)) '((foo) :magic (bar))) ;; => ((foo) (magical) (code) (bar))

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

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)

Create a shallow copy of list.

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

Functions returning a sublist of the original list.

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

Alias: -select.

This function's anaphoric counterpart is --filter.

For similar operations, see also -keep and -remove.

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

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

Alias: -reject.

This function's anaphoric counterpart is --remove.

For similar operations, see also -keep and -filter.

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

Remove the first item from list for which pred returns non-nil. This is a non-destructive operation, but only the front of list leading up to the removed item is a copy; the rest is list's original tail. If no item is removed, then the result is a complete copy.

Alias: -reject-first.

This function's anaphoric counterpart is --remove-first.

See also -map-first, -remove-item, and -remove-last.

(-remove-first #'natnump '(-2 -1 0 1 2)) ;; => (-2 -1 1 2)
(-remove-first #'stringp '(1 2 "first" "second")) ;; => (1 2 "second")
(--remove-first (> it 3) '(1 2 3 4 5 6)) ;; => (1 2 3 5 6)

Remove the last item from list for which pred returns non-nil. The result is a copy of list regardless of whether an element is removed.

Alias: -reject-last.

This function's anaphoric counterpart is --remove-last.

See also -map-last, -remove-item, and -remove-first.

(-remove-last #'natnump '(1 3 5 4 7 8 10 -11)) ;; => (1 3 5 4 7 8 -11)
(-remove-last #'stringp '(1 2 "last" "second")) ;; => (1 2 "last")
(--remove-last (> it 3) '(1 2 3 4 5 6 7 8 9 10)) ;; => (1 2 3 4 5 6 7 8 9)

Return a copy of list with all occurrences of item removed. The comparison is done with equal.

(-remove-item 3 '(1 2 3 2 3 4 5 3)) ;; => (1 2 2 4 5)
(-remove-item 'foo '(foo bar baz foo)) ;; => (bar baz)
(-remove-item "bob" '("alice" "bob" "eve" "bob")) ;; => ("alice" "eve")

Return a copy of list with all nil items removed.

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

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)

Return a copy of the first n items in list. Return a copy of list if it contains n items or fewer. Return nil if n is zero or less.

See also: -take-last.

(-take 3 '(1 2 3 4 5)) ;; => (1 2 3)
(-take 17 '(1 2 3 4 5)) ;; => (1 2 3 4 5)
(-take 0 '(1 2 3 4 5)) ;; => ()

Return a copy of the last n items of list in order. Return a copy of list if it contains n items or fewer. Return nil if n is zero or less.

See also: -take.

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

Return the tail (not a copy) of list without the first n items. Return nil if list contains n items or fewer. Return list if n is zero or less.

For another variant, see also -drop-last.

(-drop 3 '(1 2 3 4 5)) ;; => (4 5)
(-drop 17 '(1 2 3 4 5)) ;; => ()
(-drop 0 '(1 2 3 4 5)) ;; => (1 2 3 4 5)

Return a copy of list without its last n items. Return a copy of list if n is zero or less. Return nil if list contains n items or fewer.

See also: -drop.

(-drop-last 3 '(1 2 3 4 5)) ;; => (1 2)
(-drop-last 17 '(1 2 3 4 5)) ;; => ()
(-drop-last 0 '(1 2 3 4 5)) ;; => (1 2 3 4 5)

Take successive items from list for which pred returns non-nil. pred is a function of one argument. Return a new list of the successive elements from the start of list for which pred returns non-nil.

This function's anaphoric counterpart is --take-while.

For another variant, see also -drop-while.

(-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 successive items from list for which pred returns non-nil. pred is a function of one argument. Return the tail (not a copy) of list starting from its first element for which pred returns nil.

This function's anaphoric counterpart is --drop-while.

For another variant, see also -take-while.

(-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)

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")

Select columns from table.

table is a list of lists where each element represents one row. It is assumed each row has the same length.

Each row is transformed such that only the specified columns are selected.

See also: -select-column, -select-by-indices

(-select-columns '(0 2) '((1 2 3) (a b c) (:a :b :c))) ;; => ((1 3) (a c) (:a :c))
(-select-columns '(1) '((1 2 3) (a b c) (:a :b :c))) ;; => ((2) (b) (:b))
(-select-columns nil '((1 2 3) (a b c) (:a :b :c))) ;; => (nil nil nil)

Select column from table.

table is a list of lists where each element represents one row. It is assumed each row has the same length.

The single selected column is returned as a list.

See also: -select-columns, -select-by-indices

(-select-column 1 '((1 2 3) (a b c) (:a :b :c))) ;; => (2 b :b)

Functions returning a modified copy of the input list.

Return a new list of the non-nil results of applying fn to each item in list. Like -filter, but returns the non-nil results of fn instead of the corresponding elements of list.

Its anaphoric counterpart is --keep.

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

Concatenate all the arguments and make the result a list. The result is a list whose elements are the elements of all the arguments. Each argument may be a list, vector or string.

All arguments except the last argument are copied. The last argument is just used as the tail of the new list.

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

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

Note that because nil represents a list of zero elements (an empty list), any mention of nil in l will disappear after flattening. If you need to preserve nils, consider -flatten-n or map them to some unique symbol and then map them back.

Conses of two atoms are considered "terminals", that is, they aren't flattened further.

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 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 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

Replace the first occurrence of old with new in list.

Elements are compared using equal.

See also: -map-first

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

Replace the last occurrence of old with new in list.

Elements are compared using equal.

See also: -map-last

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

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)

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)

Use func to update the nth element of list. Return a copy of list where the nth element is replaced with the result of calling func on it.

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")

Return list with its element at index n removed. That is, remove any element selected as (nth n list) from list and return the result.

This is a non-destructive operation: parts of list (but not necessarily all of it) are copied as needed to avoid destructively modifying it.

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

(-remove-at 0 '(a b c)) ;; => (b c)
(-remove-at 1 '(a b c)) ;; => (a c)
(-remove-at 2 '(a b c)) ;; => (a b)

Return list with its elements at indices removed. That is, for each index i in indices, remove any element selected as (nth i list) from list.

This is a non-destructive operation: parts of list (but not necessarily all of it) are copied as needed to avoid destructively modifying it.

See also: -remove-at, -remove.

(-remove-at-indices '(0) '(a b c d e)) ;; => (b c d e)
(-remove-at-indices '(1 3) '(a b c d e)) ;; => (a c e)
(-remove-at-indices '(4 0 2) '(a b c d e)) ;; => (b d)

Functions reducing lists to a single value (which may also be a list).

Reduce the function fn across list, starting with init. Return the result of applying fn to init and the first element of list, then applying fn to that result and the second element, etc. If list is empty, return init without calling fn.

This function's anaphoric counterpart is --reduce-from.

For other folds, see also -reduce and -reduce-r.

(-reduce-from #'- 10 '(1 2 3)) ;; => 4
(-reduce-from #'list 10 '(1 2 3)) ;; => (((10 1) 2) 3)
(--reduce-from (concat acc " " it) "START" '("a" "b" "c")) ;; => "START a b c"

Reduce the function fn across list in reverse, starting with init. Return the result of applying fn to the last element of list and init, then applying fn to the second-to-last element and the previous result of fn, etc. That is, the first argument of fn is the current element, and its second argument the accumulated value. If list is empty, return init without calling fn.

This function is like -reduce-from but the operation associates from the right rather than left. In other words, it starts from the end of list and flips the arguments to fn. Conceptually, it is like replacing the conses in list with applications of fn, and its last link with init, and evaluating the resulting expression.

This function's anaphoric counterpart is --reduce-r-from.

For other folds, see also -reduce-r and -reduce.

(-reduce-r-from #'- 10 '(1 2 3)) ;; => -8
(-reduce-r-from #'list 10 '(1 2 3)) ;; => (1 (2 (3 10)))
(--reduce-r-from (concat it " " acc) "END" '("a" "b" "c")) ;; => "a b c END"

Reduce the function fn across list. Return the result of applying fn to the first two elements of list, then applying fn to that result and the third element, etc. If list contains a single element, return it without calling fn. If list is empty, return the result of calling fn with no arguments.

This function's anaphoric counterpart is --reduce.

For other folds, see also -reduce-from and -reduce-r.

(-reduce #'- '(1 2 3 4)) ;; => -8
(-reduce #'list '(1 2 3 4)) ;; => (((1 2) 3) 4)
(--reduce (format "%s-%d" acc it) '(1 2 3)) ;; => "1-2-3"

Reduce the function fn across list in reverse. Return the result of applying fn to the last two elements of list, then applying fn to the third-to-last element and the previous result of fn, etc. That is, the first argument of fn is the current element, and its second argument the accumulated value. If list contains a single element, return it without calling fn. If list is empty, return the result of calling fn with no arguments.

This function is like -reduce but the operation associates from the right rather than left. In other words, it starts from the end of list and flips the arguments to fn. Conceptually, it is like replacing the conses in list with applications of fn, ignoring its last link, and evaluating the resulting expression.

This function's anaphoric counterpart is --reduce-r.

For other folds, see also -reduce-r-from and -reduce.

(-reduce-r #'- '(1 2 3 4)) ;; => -2
(-reduce-r #'list '(1 2 3 4)) ;; => (1 (2 (3 4)))
(--reduce-r (format "%s-%d" acc it) '(1 2 3)) ;; => "3-2-1"

Return a list of fn's intermediate reductions across list. That is, a list of the intermediate values of the accumulator when -reduce-from (which see) is called with the same arguments.

This function's anaphoric counterpart is --reductions-from.

For other folds, see also -reductions and -reductions-r.

(-reductions-from #'max 0 '(2 1 4 3)) ;; => (0 2 2 4 4)
(-reductions-from #'* 1 '(1 2 3 4)) ;; => (1 1 2 6 24)
(--reductions-from (format "(FN %s %d)" acc it) "INIT" '(1 2 3)) ;; => ("INIT" "(FN INIT 1)" "(FN (FN INIT 1) 2)" "(FN (FN (FN INIT 1) 2) 3)")

Return a list of fn's intermediate reductions across reversed list. That is, a list of the intermediate values of the accumulator when -reduce-r-from (which see) is called with the same arguments.

This function's anaphoric counterpart is --reductions-r-from.

For other folds, see also -reductions and -reductions-r.

(-reductions-r-from #'max 0 '(2 1 4 3)) ;; => (4 4 4 3 0)
(-reductions-r-from #'* 1 '(1 2 3 4)) ;; => (24 24 12 4 1)
(--reductions-r-from (format "(FN %d %s)" it acc) "INIT" '(1 2 3)) ;; => ("(FN 1 (FN 2 (FN 3 INIT)))" "(FN 2 (FN 3 INIT))" "(FN 3 INIT)" "INIT")

Return a list of fn's intermediate reductions across list. That is, a list of the intermediate values of the accumulator when -reduce (which see) is called with the same arguments.

This function's anaphoric counterpart is --reductions.

For other folds, see also -reductions and -reductions-r.

(-reductions #'+ '(1 2 3 4)) ;; => (1 3 6 10)
(-reductions #'* '(1 2 3 4)) ;; => (1 2 6 24)
(--reductions (format "(FN %s %d)" acc it) '(1 2 3)) ;; => (1 "(FN 1 2)" "(FN (FN 1 2) 3)")

Return a list of fn's intermediate reductions across reversed list. That is, a list of the intermediate values of the accumulator when -reduce-r (which see) is called with the same arguments.

This function's anaphoric counterpart is --reductions-r.

For other folds, see also -reductions-r-from and -reductions.

(-reductions-r #'+ '(1 2 3 4)) ;; => (10 9 7 4)
(-reductions-r #'* '(1 2 3 4)) ;; => (24 24 12 4)
(--reductions-r (format "(FN %d %s)" it acc) '(1 2 3)) ;; => ("(FN 1 (FN 2 3))" "(FN 2 3)" 3)

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

Return the sum of list.

(-sum ()) ;; => 0
(-sum '(1)) ;; => 1
(-sum '(1 2 3 4)) ;; => 10

Return a list with running sums of items in list. list must be non-empty.

(-running-sum '(1 2 3 4)) ;; => (1 3 6 10)
(-running-sum '(1)) ;; => (1)
(-running-sum ()) ;; Wrong type argument: consp, nil

Return the product of list.

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

Return a list with running products of items in list. list must be non-empty.

(-running-product '(1 2 3 4)) ;; => (1 2 6 24)
(-running-product '(1)) ;; => (1)
(-running-product ()) ;; Wrong type argument: consp, nil

Return all prefixes of list.

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

Return all suffixes of list.

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

Return the longest common prefix of lists.

(-common-prefix '(1)) ;; => (1)
(-common-prefix '(1 2) '(3 4) '(1 2)) ;; => ()
(-common-prefix '(1 2) '(1 2 3) '(1 2 3 4)) ;; => (1 2)

Return the longest common suffix of lists.

(-common-suffix '(1)) ;; => (1)
(-common-suffix '(1 2) '(3 4) '(1 2)) ;; => ()
(-common-suffix '(1 2 3 4) '(2 3 4) '(3 4)) ;; => (3 4)

Return the smallest value from list of numbers or markers.

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

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)

Return the largest value from list of numbers or markers.

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

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)

Count the occurrences of each distinct element of list.

Return an alist of (element . n), where each element occurs n times in list.

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

See also -count and -group-by.

(-frequencies ()) ;; => ()
(-frequencies '(1 2 3 1 2 1)) ;; => ((1 . 3) (2 . 2) (3 . 1))
(let ((-compare-fn #'string=)) (-frequencies '(a "a"))) ;; => ((a . 2))

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

Return a list of iterated applications of fun to init.

This means a list of the 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)

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))

Return a new list of length n with each element being x. Return nil if n is less than 1.

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

Return an infinite circular copy of list. The returned list cycles through the elements of list and repeats 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-lists (-cycle '(3)) '(1 2)) ;; => ((3 1) (3 2))

Reductions of one or more lists to a boolean value.

Return (pred x) for the first list item where (pred x) is non-nil, else nil.

Alias: -any.

This function's anaphoric counterpart is --some.

(-some #'stringp '(1 "2" 3)) ;; => t
(--some (string-match-p "x" it) '("foo" "axe" "xor")) ;; => 1
(--some (= it-index 3) '(0 1 2)) ;; => nil

Return non-nil if pred returns non-nil for all items in list. If so, return the last such result of pred. Otherwise, once an item is reached for which pred returns nil, return nil without calling pred on any further list elements.

This function is like -every-p, but on success returns the last non-nil result of pred instead of just t.

This function's anaphoric counterpart is --every.

(-every #'numberp '(1 2 3)) ;; => t
(--every (string-match-p "x" it) '("axe" "xor")) ;; => 0
(--every (= it it-index) '(0 1 3)) ;; => nil

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

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

(-any? #'numberp '(nil 0 t)) ;; => t
(-any? #'numberp '(nil t t)) ;; => nil
(-any? #'null '(1 3 5)) ;; => nil

Return t if (pred x) is non-nil for all x in list, else nil. In the latter case, stop after the first x for which (pred x) is nil, without calling pred on any subsequent elements of list.

The similar function -every is more widely useful, since it returns the last non-nil result of pred instead of just t on success.

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

This function's anaphoric counterpart is --all?.

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

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

Return t if different list items both satisfy and do not satisfy pred. That is, if pred returns both nil for at least one item, and non-nil for at least one other item in list. Return nil if all items satisfy the predicate or none of them do.

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

Return non-nil if list contains element.

The test for equality is done with equal, or with -compare-fn if that is non-nil. As with member, the return value is actually the tail of list whose car is element.

Alias: -contains-p.

(-contains? '(1 2 3) 1) ;; => (1 2 3)
(-contains? '(1 2 3) 2) ;; => (2 3)
(-contains? '(1 2 3) 4) ;; => ()

Return non-nil if prefix is a 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

Return non-nil if suffix is a 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

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

Return non-nil if obj is a true cons pair. That is, a cons (a . b) where b is not a list.

Alias: -cons-pair-p.

(-cons-pair? '(1 . 2)) ;; => t
(-cons-pair? '(1 2)) ;; => nil
(-cons-pair? '(1)) ;; => nil

Functions partitioning the input list into a list of lists.

Split list into two sublists after the nth element. The result is a list of two elements (take drop) where take is a new list of the first n elements of list, and drop is the remaining elements of list (not a copy). take and drop are like the results of -take and -drop, respectively, but the split is done in a single list traversal.

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

Split list into a prefix satisfying pred, and the rest. The first sublist is the prefix of list with successive elements satisfying pred, and the second sublist is the remaining elements that do not. The result is like performing

((-take-while `pred` `list`) (-drop-while `pred` `list`))

but in no more than a single pass through 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 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 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))

Split list into two sublists based on whether items satisfy pred. The result is like performing

((-filter `pred` `list`) (-remove `pred` `list`))

but in a single pass through 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)))

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))

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 list into sublists of length n that are step items apart. Like -partition-all-in-steps, but 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 list into sublists of length n that are step items apart. Adjacent groups may overlap if n exceeds the step stride. Trailing 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))

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))

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))

Partition list after each element for which pred returns non-nil.

This function's anaphoric counterpart is --partition-after-pred.

(-partition-after-pred #'booleanp ()) ;; => ()
(-partition-after-pred #'booleanp '(t t)) ;; => ((t) (t))
(-partition-after-pred #'booleanp '(0 0 t t 0 t)) ;; => ((0 0 t) (t) (0 t))

Partition directly before each time pred is true on an element of list.

(-partition-before-pred #'booleanp ()) ;; => ()
(-partition-before-pred #'booleanp '(0 t)) ;; => ((0) (t))
(-partition-before-pred #'booleanp '(0 0 t 0 t t)) ;; => ((0 0) (t 0) (t) (t))

Partition directly before each time item appears in list.

(-partition-before-item 3 ()) ;; => ()
(-partition-before-item 3 '(1)) ;; => ((1))
(-partition-before-item 3 '(3)) ;; => ((3))

Partition directly after each time item appears in list.

(-partition-after-item 3 ()) ;; => ()
(-partition-after-item 3 '(1)) ;; => ((1))
(-partition-after-item 3 '(3)) ;; => ((3))

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"))

Functions retrieving or sorting based on list indices and related predicates.

Return the first index of elem in list. That is, the index within list of the first element that is equal to elem. Return nil if there is no such element.

See also: -find-index.

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

Return the list of indices at which elem appears in list. That is, the indices of all elements of list equal to elem, in the same ascending order as they appear in list.

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

Return the index of the first item satisfying pred in list. Return nil if no such item is found.

pred is called with one argument, the current list element, until it returns non-nil, at which point the search terminates.

This function's anaphoric counterpart is --find-index.

See also: -first, -find-last-index.

(-find-index #'numberp '(a b c)) ;; => nil
(-find-index #'natnump '(1 0 -1)) ;; => 0
(--find-index (> it 5) '(2 4 1 6 3 3 5 8)) ;; => 3

Return the index of the last item satisfying pred in list. Return nil if no such item is found.

Predicate pred is called with one argument each time, namely the current list element.

This function's anaphoric counterpart is --find-last-index.

See also: -last, -find-index.

(-find-last-index #'numberp '(a b c)) ;; => nil
(--find-last-index (> it 5) '(2 7 1 6 3 8 5 2)) ;; => 5
(-find-last-index (-partial #'string< 'a) '(c b a)) ;; => 1

Return the list of indices in list satisfying pred.

Each element of list in turn is passed to pred. If the result is non-nil, the index of that element in list is included in the result. The returned indices are in ascending order, i.e., in the same order as they appear in list.

This function's anaphoric counterpart is --find-indices.

See also: -find-index, -elem-indices.

(-find-indices #'numberp '(a b c)) ;; => ()
(-find-indices #'numberp '(8 1 d 2 b c a 3)) ;; => (0 1 3 7)
(--find-indices (> it 5) '(2 4 1 6 3 3 5 8)) ;; => (3 7)

Grade elements of list using comparator relation. This yields 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 elements of list using comparator relation. This yields 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)

Operations pretending lists are sets.

Return a new list of distinct elements appearing in either list1 or list2.

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

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

Return a new list with the distinct members of list1 that are not in list2.

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

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

Return a new list of distinct elements appearing in both list1 and list2.

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

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

Return the power set of list.

(-powerset ()) ;; => (nil)
(-powerset '(x y)) ;; => ((x y) (x) (y) nil)
(-powerset '(x y z)) ;; => ((x y z) (x y) (x z) (x) (y z) (y) (z) nil)

Return the distinct permutations of list.

Duplicate elements of list are determined by equal, or by -compare-fn if that is non-nil.

(-permutations ()) ;; => (nil)
(-permutations '(a a b)) ;; => ((a a b) (a b a) (b a a))
(-permutations '(a b c)) ;; => ((a b c) (a c b) (b a c) (b c a) (c a b) (c b a))

Return a copy of list with all duplicate elements removed.

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

Alias: -uniq.

(-distinct ()) ;; => ()
(-distinct '(1 1 2 3 3)) ;; => (1 2 3)
(-distinct '(t t t)) ;; => (t)

Return non-nil if list1 and list2 have the same distinct elements.

The order of the elements in the lists does not matter. The lists may be of different lengths, i.e., contain duplicate elements. The test for equality is done with equal, or with -compare-fn if that is non-nil.

Alias: -same-items-p.

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

Other list functions not fit to be classified elsewhere.

Rotate list n places to the right (left if n is negative). 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)
(-rotate 16 '(1 2 3 4 5 6 7)) ;; => (6 7 1 2 3 4 5)

Make a new list from the elements of args. The last 2 elements of args are used as the final cons of the result, so if the final element of args is not a list, the result is a dotted list. With no args, return nil.

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

Append elem to the end of the list.

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

If any elements are given, append them 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))

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

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

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")

Return a list containing count numbers. Starts from start and adds step each time. The default start is zero, the default step is 1. This function takes its name from the corresponding primitive in the apl language.

(-iota 6) ;; => (0 1 2 3 4 5)
(-iota 4 2.5 -2) ;; => (2.5 0.5 -1.5 -3.5)
(-iota -1) ;; Wrong type argument: natnump, -1

Zip list1 and list2 into a new list using the function fn. That is, apply fn pairwise taking as first argument the next element of list1 and as second argument the next element of list2 at the corresponding position. The result is as long as the shorter list.

This function's anaphoric counterpart is --zip-with.

For other zips, see also -zip-lists and -zip-fill.

(-zip-with #'+ '(1 2 3 4) '(5 6 7)) ;; => (6 8 10)
(-zip-with #'cons '(1 2 3) '(4 5 6 7)) ;; => ((1 . 4) (2 . 5) (3 . 6))
(--zip-with (format "%s & %s" it other) '(Batman Jekyll) '(Robin Hyde)) ;; => ("Batman & Robin" "Jekyll & Hyde")

Zip list1 and list2 together.

Make a pair with the head of each list, followed by a pair with the second element of each list, and so on. The number of pairs returned is equal to the length of the shorter input list.

See also: -zip-lists.

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

Zip lists together.

Group the head of each list, followed by the second element of each list, and so on. The number of returned groupings is equal to the length of the shortest input list, and the length of each grouping is equal to the number of input lists.

The return value is always a list of proper lists, in contrast to -zip which returns a list of dotted pairs when only two input lists are provided.

See also: -zip-pair.

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

Zip lists together, padding shorter lists with fill-value. This is like -zip-lists (which see), except it retains all elements at positions beyond the end of the shortest list. The number of returned groupings is equal to the length of the longest input list, and the length of each grouping is equal to the number of input lists.

(-zip-lists-fill 0 '(1 2) '(3 4 5) '(6)) ;; => ((1 3 6) (2 4 0) (0 5 0))
(-zip-lists-fill 0 '(1 2) '(3 4) '(5 6)) ;; => ((1 3 5) (2 4 6))
(-zip-lists-fill 0 '(1 2 3) nil) ;; => ((1 0) (2 0) (3 0))

Zip lists together.

Group the head of each list, followed by the second element of each list, and so on. The number of returned groupings is equal to the length of the shortest input list, and the number of items in each grouping is equal to the number of input lists.

If only two lists are provided as arguments, return the groupings as a list of dotted pairs. Otherwise, return the groupings as a list of proper lists.

Since the return value changes form depending on the number of arguments, it is generally recommended to use -zip-lists instead, or -zip-pair if a list of dotted pairs is desired.

See also: -unzip.

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

Zip lists together, padding shorter lists with fill-value. This is like -zip (which see), except it retains all elements at positions beyond the end of the shortest list. The number of returned groupings is equal to the length of the longest input list, and the length of each grouping is equal to the number of input lists.

Since the return value changes form depending on the number of arguments, it is generally recommended to use -zip-lists-fill instead, unless a list of dotted pairs is explicitly desired.

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

Unzip lists.

This works just like -zip-lists (which see), but takes a list of lists instead of a variable number of arguments, such that

(-unzip-lists (-zip-lists `args`...))

is identity (given that the lists comprising args are of the same length).

(-unzip-lists (-zip-lists '(1 2) '(3 4) '(5 6))) ;; => ((1 2) (3 4) (5 6))
(-unzip-lists '((1 2 3) (4 5) (6 7) (8 9))) ;; => ((1 4 6 8) (2 5 7 9))
(-unzip-lists '((1 2 3) (4 5 6))) ;; => ((1 4) (2 5) (3 6))

Unzip lists.

This works just like -zip (which see), but takes a list of lists instead of a variable number of arguments, such that

(-unzip (-zip `l1` `l2` `l3` ...))

is identity (given that the lists are of the same length, and that -zip is not called with two arguments, because of the caveat described in its docstring).

Note in particular that calling -unzip on a list of two lists will return a list of dotted pairs.

Since the return value changes form depending on the number of lists, it is generally recommended to use -unzip-lists instead.

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

Pad each of lists with fill-value until they all have equal lengths.

Ensure all lists are as long as the longest one by repeatedly appending fill-value to the shorter lists, and return the resulting lists.

(-pad 0 ()) ;; => (nil)
(-pad 0 '(1 2) '(3 4)) ;; => ((1 2) (3 4))
(-pad 0 '(1 2) '(3 4 5 6) '(7 8 9)) ;; => ((1 2 0 0) (3 4 5 6) (7 8 9 0))

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))))

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)) (apply '-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))

Return the first item in list for which pred returns non-nil. Return nil if no such element is found.

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

Alias: -find.

This function's anaphoric counterpart is --first.

(-first #'natnump '(-1 0 1)) ;; => 0
(-first #'null '(1 2 3)) ;; => nil
(--first (> it 2) '(1 2 3)) ;; => 3

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"

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

See also: -second-item, -last-item, etc.

(-first-item ()) ;; => ()
(-first-item '(1 2 3 4 5)) ;; => 1
(let ((list (list 1 2 3))) (setf (-first-item list) 5) list) ;; => (5 2 3)

Return the second item of list, or nil if list is too short.

See also: -first-item, -third-item, etc.

(-second-item ()) ;; => ()
(-second-item '(1 2 3 4 5)) ;; => 2
(let ((list (list 1 2))) (setf (-second-item list) 5) list) ;; => (1 5)

Return the third item of list, or nil if list is too short.

See also: -second-item, -fourth-item, etc.

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

Return the fourth item of list, or nil if list is too short.

See also: -third-item, -fifth-item, etc.

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

Return the fifth item of list, or nil if list is too short.

See also: -fourth-item, -last-item, etc.

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

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

See also: -first-item, etc.

(-last-item ()) ;; => ()
(-last-item '(1 2 3 4 5)) ;; => 5
(let ((list (list 1 2 3))) (setf (-last-item list) 5) list) ;; => (1 2 5)

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 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)

Ensure arg is a list. If arg is already a list, return it as is (not a copy). Otherwise, return a new list with arg as its only element.

Another supported calling convention is (-list &rest args). In this case, if arg is not a list, a new list with all of args as elements is returned. This use is supported for backward compatibility and is otherwise deprecated.

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

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))) ;; => ((1) (2) (3))
(let ((l '((starwars scifi) (jedi starwars warrior)))) (--fix (-uniq (--mapcat (cons it (cdr (assq it l))) it)) '(jedi book))) ;; => (jedi starwars warrior scifi book)

Functions pretending lists are trees.

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)

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)

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)))

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>"

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)

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

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) "}" '((elisp-mode (foo (bar . booze)) (baz . qux)) (c-mode (foo . bla) (bum . bam))))) ;; => "{elisp-mode : {foo : {bar -> booze}, baz -> qux}, c-mode : {foo -> bla, bum -> bam}}"

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 (list (list 1))) (b (-clone a))) (setcar (car a) 2) b) ;; => ((1))

Macros that conditionally combine sequential forms for brevity or readability.

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)

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

Starting with the value of x, thread each expression through forms.

Insert x at the position signified by the symbol it in the first form. If there are more forms, insert the first form at the position signified by it in the second form, etc.

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

Starting with value, thread variable through forms.

In the first form, bind variable to value. In the second form, bind variable to the result of the first form, and so forth.

(-as-> 3 my-var (1+ my-var) (list my-var) (mapcar (lambda (ele) (* 2 ele)) my-var)) ;; => (8)
(-as-> 3 my-var 1+) ;; => 4
(-as-> 3 my-var) ;; => 3

When expr is non-nil, thread it through the first form (via ->), and when that result is non-nil, through the next form, etc.

(-some-> '(2 3 5)) ;; => (2 3 5)
(-some-> 5 square) ;; => 25
(-some-> 5 even? square) ;; => nil

When expr is non-nil, thread it through the first form (via ->>), and when that result is non-nil, through the next form, etc.

(-some->> '(1 2 3) (-map 'square)) ;; => (1 4 9)
(-some->> '(1 3 5) (-last 'even?) (+ 100)) ;; => nil
(-some->> '(2 4 6) (-last 'even?) (+ 100)) ;; => 106

Thread expr through forms via -->, while the result is non-nil. When expr evaluates to non-nil, thread the result through the first of forms, and when that result is non-nil, thread it through the next form, etc.

(-some--> "def" (concat "abc" it "ghi")) ;; => "abcdefghi"
(-some--> nil (concat "abc" it "ghi")) ;; => nil
(-some--> '(0 1) (-remove #'natnump it) (append it it) (-map #'1+ it)) ;; => ()

Evaluate init and pass it as argument to forms with ->. The result of evaluating init is threaded through each of forms individually using ->, which see. The return value is result, which forms may have modified by side effect.

(-doto (list 1 2 3) pop pop) ;; => (3)
(-doto (cons 1 2) (setcar 3) (setcdr 4)) ;; => (3 . 4)
(gethash 'k (--doto (make-hash-table) (puthash 'k 'v it))) ;; => v

Macros that combine let and let* with destructuring and flow control.

If val evaluates to non-nil, bind it to var and execute body.

Note: binding is done according to -let.

(-when-let (match-index (string-match "d" "abcd")) (+ match-index 2)) ;; => 5
(-when-let ((&plist :foo foo) (list :foo "foo")) foo) ;; => "foo"
(-when-let ((&plist :foo foo) (list :bar "bar")) foo) ;; => nil

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.

Note: binding is done according to -let*. vals are evaluated sequentially, and evaluation stops after the first nil val is encountered.

(-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 val evaluates to non-nil, bind it to var and do then, otherwise do else.

Note: binding is done according to -let.

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

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.

Note: binding is done according to -let*. vals are evaluated sequentially, and evaluation stops after the first nil val is encountered.

(-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"
(-if-let* (((_ _ x) '(nil nil 7))) x) ;; => 7

Bind variables according to varlist then eval body.

varlist is a list of lists of the form (pattern source). Each pattern is matched against the source "structurally". source is only evaluated once for each pattern. Each pattern is matched recursively, and can therefore contain sub-patterns which are matched against corresponding sub-expressions of source.

All the SOURCEs are evalled before any symbols are bound (i.e. "in parallel").

If varlist only contains one (pattern source) element, you can optionally specify it using a vector and discarding the outer-most parens. Thus

(-let ((`pattern` `source`)) ...)

becomes

(-let [`pattern` `source`] ...).

-let uses a convention of not binding places (symbols) starting with _ whenever it's possible. You can use this to skip over entries you don't care about. However, this is not always possible (as a result of implementation) and these symbols might get bound to undefined values.

Following is the overview of supported patterns. Remember that patterns can be matched recursively, so every a, b, aK in the following can be a matching construct and not necessarily a symbol/variable.

Symbol:

a - bind the `source` to `a`.  This is just like regular `let`.

Conses and lists:

(a) - bind `car` of cons/list to `a`

(a . b) - bind car of cons to `a` and `cdr` to `b`

(a b) - bind car of list to `a` and `cadr` to `b`

(a1 a2 a3 ...) - bind 0th car of list to `a1`, 1st to `a2`, 2nd to `a3`...

(a1 a2 a3 ... aN . rest) - as above, but bind the `n`th cdr to `rest`.

Vectors:

[a] - bind 0th element of a non-list sequence to `a` (works with
      vectors, strings, bit arrays...)

[a1 a2 a3 ...] - bind 0th element of non-list sequence to `a0`, 1st to
                 `a1`, 2nd to `a2`, ...
                 If the `pattern` is shorter than `source`, the values at
                 places not in `pattern` are ignored.
                 If the `pattern` is longer than `source`, an `error` is
                 thrown.

[a1 a2 a3 ... &rest rest] - as above, but bind the rest of
                            the sequence to `rest`.  This is
                            conceptually the same as improper list
                            matching (a1 a2 ... aN . rest)

Key/value stores:

(&plist key0 a0 ... keyN aN) - bind value mapped by keyK in the
                               `source` plist to aK.  If the
                               value is not found, aK is `nil`.
                               Uses `plist-get` to fetch values.

(&alist key0 a0 ... keyN aN) - bind value mapped by keyK in the
                               `source` alist to aK.  If the
                               value is not found, aK is `nil`.
                               Uses `assoc` to fetch values.

(&hash key0 a0 ... keyN aN) - bind value mapped by keyK in the
                              `source` hash table to aK.  If the
                              value is not found, aK is `nil`.
                              Uses `gethash` to fetch values.

Further, special keyword &keys supports "inline" matching of plist-like key-value pairs, similarly to &keys keyword of cl-defun.

(a1 a2 ... aN &keys key1 b1 ... keyN bK)

This binds n values from the list to a1 ... aN, then interprets the cdr as a plist (see key/value matching above).

a shorthand notation for kv-destructuring exists which allows the patterns be optionally left out and derived from the key name in the following fashion:

• a key :foo is converted into foo pattern,
• a key 'bar is converted into bar pattern,
• a key "baz" is converted into baz pattern.

That is, the entire value under the key is bound to the derived variable without any further destructuring.

This is possible only when the form following the key is not a valid pattern (i.e. not a symbol, a cons cell or a vector). Otherwise the matching proceeds as usual and in case of an invalid spec fails with an error.

Thus the patterns are normalized as follows:

 ;; derive all the missing patterns
 (&plist :foo 'bar "baz") => (&plist :foo foo 'bar bar "baz" baz)

 ;; we can specify some but not others
 (&plist :foo 'bar explicit-bar) => (&plist :foo foo 'bar explicit-bar)

 ;; nothing happens, we store :foo in x
 (&plist :foo x) => (&plist :foo x)

 ;; nothing happens, we match recursively
 (&plist :foo (a b c)) => (&plist :foo (a b c))

You can name the source using the syntax symbol &as pattern. This syntax works with lists (proper or improper), vectors and all types of maps.

(list &as a b c) (list 1 2 3)

binds a to 1, b to 2, c to 3 and list to (1 2 3).

Similarly:

(bounds &as beg . end) (cons 1 2)

binds beg to 1, end to 2 and bounds to (1 . 2).

(items &as first . rest) (list 1 2 3)

binds first to 1, rest to (2 3) and items to (1 2 3)

[vect &as _ b c] [1 2 3]

binds b to 2, c to 3 and vect to [1 2 3] (_ avoids binding as usual).

(plist &as &plist :b b) (list :a 1 :b 2 :c 3)

binds b to 2 and plist to (:a 1 :b 2 :c 3). Same for &alist and &hash.

This is especially useful when we want to capture the result of a computation and destructure at the same time. Consider the form (function-returning-complex-structure) returning a list of two vectors with two items each. We want to capture this entire result and pass it to another computation, but at the same time we want to get the second item from each vector. We can achieve it with pattern

(result &as [_ a] [_ b]) (function-returning-complex-structure)

Note: Clojure programmers may know this feature as the ":as binding". The difference is that we put the &as at the front because we need to support improper list binding.

(-let (([a (b c) d] [1 (2 3) 4])) (list a b c d)) ;; => (1 2 3 4)
(-let [(a b c . d) (list 1 2 3 4 5 6)] (list a b c d)) ;; => (1 2 3 (4 5 6))
(-let [(&plist :foo foo :bar bar) (list :baz 3 :foo 1 :qux 4 :bar 2)] (list foo bar)) ;; => (1 2)

Bind variables according to varlist then eval body.

varlist is a list of lists of the form (pattern source). Each pattern is matched against the source structurally. source is only evaluated once for each pattern.

Each source can refer to the symbols already bound by this varlist. This is useful if you want to destructure source recursively but also want to name the intermediate structures.

See -let for the list of all possible patterns.

(-let* (((a . b) (cons 1 2)) ((c . d) (cons 3 4))) (list a b c d)) ;; => (1 2 3 4)
(-let* (((a . b) (cons 1 (cons 2 3))) ((c . d) b)) (list a b c d)) ;; => (1 (2 . 3) 2 3)
(-let* (((&alist "foo" foo "bar" bar) (list (cons "foo" 1) (cons "bar" (list 'a 'b 'c)))) ((a b c) bar)) (list foo a b c bar)) ;; => (1 a b c (a b c))

Return a lambda which destructures its input as match-form and executes body.

Note that you have to enclose the match-form in a pair of parens, such that:

(-lambda (x) body)
(-lambda (x y ...) body)

has the usual semantics of lambda. Furthermore, these get translated into normal lambda, so there is no performance penalty.

See -let for a description of the destructuring mechanism.

(-map (-lambda ((x y)) (+ x y)) '((1 2) (3 4) (5 6))) ;; => (3 7 11)
(-map (-lambda ([x y]) (+ x y)) '([1 2] [3 4] [5 6])) ;; => (3 7 11)
(funcall (-lambda ((_ . a) (_ . b)) (-concat a b)) '(1 2 3) '(4 5 6)) ;; => (2 3 5 6)

Bind each match-form to the value of its val.

match-form destructuring is done according to the rules of -let.

This macro allows you to bind multiple variables by destructuring the value, so for example:

(-setq (a b) x
       (&plist :c c) plist)

expands roughly speaking to the following code

(setq a (car x)
      b (cadr x)
      c (plist-get plist :c))

Care is taken to only evaluate each val once so that in case of multiple assignments it does not cause unexpected side effects.

(let (a) (-setq a 1) a) ;; => 1
(let (a b) (-setq (a b) (list 1 2)) (list a b)) ;; => (1 2)
(let (c) (-setq (&plist :c c) (list :c "c")) c) ;; => "c"

Functions iterating over lists for side effect only.

Call fn on each element of list. Return nil; this function is intended for side effects.

Its anaphoric counterpart is --each.

For access to the current element's index in list, see -each-indexed.

(let (l) (-each '(1 2 3) (lambda (x) (push x l))) l) ;; => (3 2 1)
(let (l) (--each '(1 2 3) (push it l)) l) ;; => (3 2 1)
(-each '(1 2 3) #'identity) ;; => nil

Call fn on each item in list, while (pred item) is non-nil. Once an item is reached for which pred returns nil, fn is no longer called. Return nil; this function is intended for side effects.

Its anaphoric counterpart is --each-while.

(let (l) (-each-while '(2 4 5 6) #'even? (lambda (x) (push x l))) l) ;; => (4 2)
(let (l) (--each-while '(1 2 3 4) (< it 3) (push it l)) l) ;; => (2 1)
(let ((s 0)) (--each-while '(1 3 4 5) (< it 5) (setq s (+ s it))) s) ;; => 8

Call fn on each index and element of list. For each item at index in list, call (funcall fn index item). Return nil; this function is intended for side effects.

See also: -map-indexed.

(let (l) (-each-indexed '(a b c) (lambda (i x) (push (list x i) l))) l) ;; => ((c 2) (b 1) (a 0))
(let (l) (--each-indexed '(a b c) (push (list it it-index) l)) l) ;; => ((c 2) (b 1) (a 0))
(let (l) (--each-indexed () (push it l)) l) ;; => ()