dash.el/dash.el

;;; dash.el --- A modern list library for Emacs

;; Copyright (C) 2012 Magnar Sveen

;; Author: Magnar Sveen <magnars@gmail.com>
;; Version: 1.5.0
;; 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/>.

;;; Commentary:

;; A modern list api for Emacs.
;;
;; See documentation on https://github.com/magnars/dash.el#functions

;;; Code:

(defmacro !cons (car cdr)
  "Destructive: Sets CDR to the cons of CAR and CDR."
  `(setq ,cdr (cons ,car ,cdr)))

(defmacro !cdr (list)
  "Destructive: Sets LIST to the cdr of LIST."
  `(setq ,list (cdr ,list)))

(defmacro --each (list &rest body)
  "Anaphoric form of `-each'."
  (declare (debug t))
  (let ((l (make-symbol "list")))
    `(let ((,l ,list)
           (it-index 0))
       (while ,l
         (let ((it (car ,l)))
           ,@body)
         (setq it-index (1+ it-index))
         (!cdr ,l)))))

(put '--each 'lisp-indent-function 1)

(defun -each (list fn)
  "Calls FN with every item in LIST. Returns nil, used for side-effects only."
  (--each list (funcall fn it)))

(defmacro --each-while (list pred &rest body)
  "Anaphoric form of `-each-while'."
  (let ((l (make-symbol "list"))
        (c (make-symbol "continue")))
    `(let ((,l ,list)
           (,c t))
       (while (and ,l ,c)
         (let ((it (car ,l)))
           (if (not ,pred) (setq ,c nil) ,@body))
         (!cdr ,l)))))

(put '--each-while 'lisp-indent-function 2)

(defun -each-while (list pred fn)
  "Calls FN with every item in LIST while (PRED item) is non-nil.
Returns nil, used for side-effects only."
  (--each-while list (funcall pred it) (funcall fn it)))

(defmacro --dotimes (num &rest body)
  "Repeatedly executes BODY (presumably for side-effects) with `it` bound to integers from 0 through n-1."
  `(let ((it 0))
     (while (< it ,num)
       ,@body
       (setq it (1+ it)))))

(put '--dotimes 'lisp-indent-function 1)

(defun -dotimes (num fn)
  "Repeatedly calls FN (presumably for side-effects) passing in integers from 0 through n-1."
  (--dotimes num (funcall fn it)))

(defun -map (fn list)
  "Returns a new list consisting of the result of applying FN to the items in LIST."
  (mapcar fn list))

(defmacro --map (form list)
  "Anaphoric form of `-map'."
  (declare (debug t))
  `(mapcar (lambda (it) ,form) ,list))

(defmacro --reduce-from (form initial-value list)
  "Anaphoric form of `-reduce-from'."
  `(let ((acc ,initial-value))
     (--each ,list (setq acc ,form))
     acc))

(defun -reduce-from (fn initial-value list)
  "Returns the result of applying FN to INITIAL-VALUE and the
first item in LIST, then applying FN to that result and the 2nd
item, etc. If LIST contains no items, returns INITIAL-VALUE and
FN is not called.

In the anaphoric form `--reduce-from', the accumulated value is
exposed as `acc`."
  (--reduce-from (funcall fn acc it) initial-value list))

(defmacro --reduce (form list)
  "Anaphoric form of `-reduce'."
  (let ((lv (make-symbol "list-value")))
    `(let ((,lv ,list))
       (if ,lv
           (--reduce-from ,form (car ,lv) (cdr ,lv))
         (let (acc it) ,form)))))

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

In the anaphoric form `--reduce', the accumulated value is
exposed as `acc`."
  (if list
      (-reduce-from fn (car list) (cdr list))
    (funcall fn)))

(defun -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."
  (if (not list) initial-value
    (funcall fn (car list) (-reduce-r-from fn initial-value (cdr list)))))

(defmacro --reduce-r-from (form initial-value list)
  "Anaphoric version of `-reduce-r-from'."
  `(-reduce-r-from (lambda (&optional it acc) ,form) ,initial-value ,list))

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

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

Note: this function works the same as `-reduce' but the operation
associates from right instead of from left."
  (cond
   ((not list) (funcall fn))
   ((not (cdr list)) (car list))
   (t (funcall fn (car list) (-reduce-r fn (cdr list))))))

(defmacro --reduce-r (form list)
  "Anaphoric version of `-reduce-r'."
  `(-reduce-r (lambda (&optional it acc) ,form) ,list))

(defmacro --filter (form list)
  "Anaphoric form of `-filter'."
  (let ((r (make-symbol "result")))
    `(let (,r)
       (--each ,list (when ,form (!cons it ,r)))
       (nreverse ,r))))

(defun -filter (pred list)
  "Returns a new list of the items in LIST for which PRED returns a non-nil value.

Alias: `-select'"
  (--filter (funcall pred it) list))

(defalias '-select '-filter)
(defalias '--select '--filter)

(defmacro --remove (form list)
  "Anaphoric form of `-remove'."
  (declare (debug t))
  `(--filter (not ,form) ,list))

(defun -remove (pred list)
  "Returns a new list of the items in LIST for which PRED returns nil.

Alias: `-reject'"
  (--remove (funcall pred it) list))

(defalias '-reject '-remove)
(defalias '--reject '--remove)

(defmacro --keep (form list)
  "Anaphoric form of `-keep'."
  (let ((r (make-symbol "result"))
        (m (make-symbol "mapped")))
    `(let (,r)
       (--each ,list (let ((,m ,form)) (when ,m (!cons ,m ,r))))
       (nreverse ,r))))

(defun -keep (fn list)
  "Returns a new list of the non-nil results of applying FN to the items in LIST."
  (--keep (funcall fn it) list))

(defmacro --map-when (pred rep list)
  "Anaphoric form of `-map-when'."
  (let ((r (make-symbol "result")))
    `(let (,r)
       (--each ,list (!cons (if ,pred ,rep it) ,r))
       (nreverse ,r))))

(defmacro --map-indexed (form list)
  "Anaphoric form of `-map-indexed'."
  (let ((r (make-symbol "result")))
    `(let (,r)
       (--each ,list
         (!cons ,form ,r))
       (nreverse ,r))))

(defun -map-indexed (fn list)
  "Returns a new list consisting of the result of (FN index item) for each item in LIST.

In the anaphoric form `--map-indexed', the index is exposed as `it-index`."
  (--map-indexed (funcall fn it-index it) list))

(defun -map-when (pred rep list)
  "Returns a new list where the elements in LIST that does not match the PRED function
are unchanged, and where the elements in LIST that do match the PRED function are mapped
through the REP function."
  (--map-when (funcall pred it) (funcall rep it) list))

(defalias '--replace-where '--map-when)
(defalias '-replace-where '-map-when)

(defun -flatten (l)
  "Takes a nested list L and returns its contents as a single, flat list."
  (if (and (listp l) (listp (cdr l)))
      (-mapcat '-flatten l)
    (list l)))

(defun -concat (&rest lists)
  "Returns a new list with the concatenation of the elements in the supplied LISTS."
  (apply 'append lists))

(defmacro --mapcat (form list)
  "Anaphoric form of `-mapcat'."
  (declare (debug t))
  `(apply 'append (--map ,form ,list)))

(defun -mapcat (fn list)
  "Returns the concatenation of the result of mapping FN over LIST.
Thus function FN should return a list."
  (--mapcat (funcall fn it) list))

(defun -cons* (&rest args)
  "Makes a new list from the elements of ARGS.

The last 2 members of ARGS are used as the final cons of the
result so if the final member of ARGS is not a list the result is
a dotted list."
  (let (res)
    (--each
        args
      (cond
       ((not res)
        (setq res it))
       ((consp res)
        (setcdr res (cons (cdr res) it)))
       (t
        (setq res (cons res it)))))
    res))

(defmacro --first (form list)
  "Anaphoric form of `-first'."
  (let ((n (make-symbol "needle")))
    `(let (,n)
       (--each-while ,list (not ,n)
         (when ,form (setq ,n it)))
       ,n)))

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

To get the first item in the list no questions asked, use `car'."
  (--first (funcall pred it) list))

(defmacro --last (form list)
  "Anaphoric form of `-last'."
  (let ((n (make-symbol "needle")))
    `(let (,n)
       (--each ,list
         (when ,form (setq ,n it)))
       ,n)))

(defun -last (pred list)
  "Return the last x in LIST where (PRED x) is non-nil, else nil."
  (--last (funcall pred it) list))

(defmacro --count (pred list)
  "Anaphoric form of `-count'."
  (let ((r (make-symbol "result")))
    `(let ((,r 0))
       (--each ,list (when ,pred (setq ,r (1+ ,r))))
       ,r)))

(defun -count (pred list)
  "Counts the number of items in LIST where (PRED item) is non-nil."
  (--count (funcall pred it) list))

(defun ---truthy? (val)
  (not (null val)))

(defmacro --any? (form list)
  "Anaphoric form of `-any?'."
  `(---truthy? (--first ,form ,list)))

(defun -any? (pred list)
  "Returns t if (PRED x) is non-nil for any x in LIST, else nil.

Alias: `-some?'"
  (--any? (funcall pred it) list))

(defalias '-some? '-any?)
(defalias '--some? '--any?)

(defalias '-any-p '-any?)
(defalias '--any-p '--any?)
(defalias '-some-p '-any?)
(defalias '--some-p '--any?)

(defmacro --all? (form list)
  "Anaphoric form of `-all?'."
  (let ((a (make-symbol "all")))
    `(let ((,a t))
       (--each-while ,list ,a (setq ,a ,form))
       (---truthy? ,a))))

(defun -all? (pred list)
  "Returns t if (PRED x) is non-nil for all x in LIST, else nil.

Alias: `-every?'"
  (--all? (funcall pred it) list))

(defalias '-every? '-all?)
(defalias '--every? '--all?)

(defalias '-all-p '-all?)
(defalias '--all-p '--all?)
(defalias '-every-p '-all?)
(defalias '--every-p '--all?)

(defmacro --none? (form list)
  "Anaphoric form of `-none?'."
  `(--all? (not ,form) ,list))

(defun -none? (pred list)
  "Returns t if (PRED x) is nil for all x in LIST, else nil."
  (--none? (funcall pred it) list))

(defalias '-none-p '-none?)
(defalias '--none-p '--none?)

(defmacro --only-some? (form list)
  "Anaphoric form of `-only-some?'."
  (let ((y (make-symbol "yes"))
        (n (make-symbol "no")))
    `(let (,y ,n)
       (--each-while ,list (not (and ,y ,n))
         (if ,form (setq ,y t) (setq ,n t)))
       (---truthy? (and ,y ,n)))))

(defun -only-some? (pred list)
  "Returns `t` if there is a mix of items in LIST that matches and does not match PRED.
Returns `nil` both if all items match the predicate, and if none of the items match the predicate."
  (--only-some? (funcall pred it) list))

(defalias '-only-some-p '-only-some?)
(defalias '--only-some-p '--only-some?)

(defun -slice (list from &optional to)
  "Return copy of LIST, starting from index FROM to index TO.
FROM or TO may be negative."
  (let ((length (length list))
        (new-list nil)
        (index 0))
    ;; to defaults to the end of the list
    (setq to (or to length))
    ;; handle negative indices
    (when (< from 0)
      (setq from (mod from length)))
    (when (< to 0)
      (setq to (mod to length)))

    ;; iterate through the list, keeping the elements we want
    (while (< index to)
      (when (>= index from)
        (!cons (car list) new-list))
      (!cdr list)
      (setq index (1+ index)))
    (nreverse new-list)))

(defun -take (n list)
  "Returns a new list of the first N items in LIST, or all items if there are fewer than N."
  (let (result)
    (--dotimes n
      (when list
        (!cons (car list) result)
        (!cdr list)))
    (nreverse result)))

(defun -drop (n list)
  "Returns the tail of LIST without the first N items."
  (--dotimes n (!cdr list))
  list)

(defmacro --take-while (form list)
  "Anaphoric form of `-take-while'."
  (let ((r (make-symbol "result")))
    `(let (,r)
       (--each-while ,list ,form (!cons it ,r))
       (nreverse ,r))))

(defun -take-while (pred list)
  "Returns a new list of successive items from LIST while (PRED item) returns a non-nil value."
  (--take-while (funcall pred it) list))

(defmacro --drop-while (form list)
  "Anaphoric form of `-drop-while'."
  (let ((l (make-symbol "list")))
    `(let ((,l ,list))
       (while (and ,l (let ((it (car ,l))) ,form))
         (!cdr ,l))
       ,l)))

(defun -drop-while (pred list)
  "Returns the tail of LIST starting from the first item for which (PRED item) returns nil."
  (--drop-while (funcall pred it) list))

(defun -split-at (n list)
  "Returns a list of ((-take N LIST) (-drop N LIST)), in no more than one pass through the list."
  (let (result)
    (--dotimes n
      (when list
        (!cons (car list) result)
        (!cdr list)))
    (list (nreverse result) list)))

(defun -insert-at (n x list)
  "Returns a list with X inserted into LIST at position N."
  (let ((split-list (-split-at n list)))
    (nconc (car split-list) (cons x (cadr split-list)))))

(defmacro --split-with (pred list)
  "Anaphoric form of `-split-with'."
  (let ((l (make-symbol "list"))
        (r (make-symbol "result"))
        (c (make-symbol "continue")))
    `(let ((,l ,list)
           (,r nil)
           (,c t))
       (while (and ,l ,c)
         (let ((it (car ,l)))
           (if (not ,pred)
               (setq ,c nil)
             (!cons it ,r)
             (!cdr ,l))))
       (list (nreverse ,r) ,l))))

(defun -split-with (pred list)
  "Returns a list of ((-take-while PRED LIST) (-drop-while PRED LIST)), in no more than one pass through the list."
  (--split-with (funcall pred it) list))

(defmacro --separate (form list)
  "Anaphoric form of `-separate'."
  (let ((y (make-symbol "yes"))
        (n (make-symbol "no")))
    `(let (,y ,n)
       (--each ,list (if ,form (!cons it ,y) (!cons it ,n)))
       (list (nreverse ,y) (nreverse ,n)))))

(defun -separate (pred list)
  "Returns a list of ((-filter PRED LIST) (-remove PRED LIST)), in one pass through the list."
  (--separate (funcall pred it) list))

(defun ---partition-all-in-steps-reversed (n step list)
  "Private: Used by -partition-all-in-steps and -partition-in-steps."
  (when (< step 1)
    (error "Step must be a positive number, or you're looking at some juicy infinite loops."))
  (let ((result nil)
        (len 0))
    (while list
      (!cons (-take n list) result)
      (setq list (-drop step list)))
    result))

(defun -partition-all-in-steps (n step list)
  "Returns a new list with the items in LIST grouped into N-sized sublists at offsets STEP apart.
The last groups may contain less than N items."
  (nreverse (---partition-all-in-steps-reversed n step list)))

(defun -partition-in-steps (n step list)
  "Returns a new list with the items in LIST grouped into N-sized sublists at offsets STEP apart.
If there are not enough items to make the last group N-sized,
those items are discarded."
  (let ((result (---partition-all-in-steps-reversed n step list)))
    (while (and result (< (length (car result)) n))
      (!cdr result))
    (nreverse result)))

(defun -partition-all (n list)
  "Returns a new list with the items in LIST grouped into N-sized sublists.
The last group may contain less than N items."
  (-partition-all-in-steps n n list))

(defun -partition (n list)
  "Returns a new list with the items in LIST grouped into N-sized sublists.
If there are not enough items to make the last group N-sized,
those items are discarded."
  (-partition-in-steps n n list))

(defmacro --partition-by (form list)
  "Anaphoric form of `-partition-by'."
  (let ((r (make-symbol "result"))
        (s (make-symbol "sublist"))
        (v (make-symbol "value"))
        (n (make-symbol "new-value"))
        (l (make-symbol "list")))
    `(let ((,l ,list))
       (when ,l
         (let* ((,r nil)
                (it (car ,l))
                (,s (list it))
                (,v ,form)
                (,l (cdr ,l)))
           (while ,l
             (let* ((it (car ,l))
                    (,n ,form))
               (unless (equal ,v ,n)
                 (!cons (nreverse ,s) ,r)
                 (setq ,s nil)
                 (setq ,v ,n))
               (!cons it ,s)
               (!cdr ,l)))
           (!cons (nreverse ,s) ,r)
           (nreverse ,r))))))

(defun -partition-by (fn list)
  "Applies FN to each item in LIST, splitting it each time FN returns a new value."
  (--partition-by (funcall fn it) list))

(defmacro --partition-by-header (form list)
  "Anaphoric form of `-partition-by-header'."
  (let ((r (make-symbol "result"))
        (s (make-symbol "sublist"))
        (h (make-symbol "header-value"))
        (b (make-symbol "seen-body?"))
        (n (make-symbol "new-value"))
        (l (make-symbol "list")))
    `(let ((,l ,list))
       (when ,l
         (let* ((,r nil)
                (it (car ,l))
                (,s (list it))
                (,h ,form)
                (,b nil)
                (,l (cdr ,l)))
           (while ,l
             (let* ((it (car ,l))
                    (,n ,form))
               (if (equal ,h, n)
                   (when ,b
                     (!cons (nreverse ,s) ,r)
                     (setq ,s nil)
                     (setq ,b nil))
                 (setq ,b t))
               (!cons it ,s)
               (!cdr ,l)))
           (!cons (nreverse ,s) ,r)
           (nreverse ,r))))))

(defun -partition-by-header (fn list)
  "Applies FN to the first item in LIST. That is the header
  value. Applies FN to each item in LIST, splitting it each time
  FN returns the header value, but only after seeing at least one
  other value (the body)."
  (--partition-by-header (funcall fn it) list))

(defmacro --group-by (form list)
  "Anaphoric form of `-group-by'."
  (let ((l (make-symbol "list"))
        (v (make-symbol "value"))
        (k (make-symbol "key"))
        (r (make-symbol "result")))
    `(let ((,l ,list)
           ,r)
       ;; Convert `list' to an alist and store it in `r'.
       (while ,l
         (let* ((,v (car ,l))
                (it ,v)
                (,k ,form)
                (kv (assoc ,k ,r)))
           (if kv
               (setcdr kv (cons ,v (cdr kv)))
             (push (list ,k ,v) ,r))
           (setq ,l (cdr ,l))))
       ;; Reverse lists in each group.
       (let ((rest ,r))
         (while rest
           (let ((kv (car rest)))
             (setcdr kv (nreverse (cdr kv))))
           (setq rest (cdr rest))))
       ;; Reverse order of keys.
       (nreverse ,r))))

(defun -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 (funcall fn it) list))

(defun -interpose (sep list)
  "Returns a new list of all elements in LIST separated by SEP."
  (let (result)
    (when list
      (!cons (car list) result)
      (!cdr list))
    (while list
      (setq result (cons (car list) (cons sep result)))
      (!cdr list))
    (nreverse result)))

(defun -interleave (&rest lists)
  "Returns a new list of the first item in each list, then the second etc."
  (let (result)
    (while (-none? 'null lists)
      (--each lists (!cons (car it) result))
      (setq lists (-map 'cdr lists)))
    (nreverse result)))

(defmacro --zip-with (form list1 list2)
  "Anaphoric form of `-zip-with'.

The elements in list1 is bound as `it`, the elements in list2 as `other`."
  (let ((r (make-symbol "result"))
        (l1 (make-symbol "list1"))
        (l2 (make-symbol "list2")))
    `(let ((,r nil)
           (,l1 ,list1)
           (,l2 ,list2))
       (while (and ,l1 ,l2)
         (let ((it (car ,l1))
               (other (car ,l2)))
           (!cons ,form ,r)
           (!cdr ,l1)
           (!cdr ,l2)))
       (nreverse ,r))))

(defun -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 (funcall fn it other) list1 list2))

(defun -zip (list1 list2)
  "Zip the two lists together.  Return the list where elements
are cons pairs with car being element from LIST1 and cdr being
element from LIST2.  The length of the returned list is the
length of the shorter one."
  (-zip-with 'cons list1 list2))

(defun -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."
  (apply 'apply-partially fn args))

(defun -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.

Requires Emacs 24 or higher."
  `(closure (t) (&rest args)
            (apply ',fn (append args ',args))))

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

Requires Emacs 24 or higher."
  (let ((r (make-symbol "result")))
    `(closure (t) (&rest args)
              (let (,r)
                (--each ',fns (!cons (apply it args) ,r))
                (nreverse ,r)))))

(defun -applify (fn)
  "Changes an n-arity function FN to a 1-arity function that
expects a list with n items as arguments"
  (apply-partially 'apply fn))

(defmacro -> (x &optional form &rest more)
  "Threads the expr through the forms. Inserts X as the second
item in the first form, making a list of it if it is not a list
already. If there are more forms, inserts the first form as the
second item in second form, etc."
  (cond
   ((null form) x)
   ((null more) (if (listp form)
                    `(,(car form) ,x ,@(cdr form))
                  (list form x)))
   (:else `(-> (-> ,x ,form) ,@more))))

(defmacro ->> (x form &rest more)
  "Threads the expr through the forms. Inserts X as the last item
in the first form, making a list of it if it is not a list
already. If there are more forms, inserts the first form as the
last item in second form, etc."
  (if (null more)
      (if (listp form)
          `(,(car form) ,@(cdr form) ,x)
        (list form x))
    `(->> (->> ,x ,form) ,@more)))

(defmacro --> (x form &rest more)
  "Threads the expr through the forms. Inserts X at the position
signified by the token `it' in the first form. If there are more
forms, inserts the first form at the position signified by `it'
in in second form, etc."
  (if (null more)
      (if (listp form)
          (--map-when (eq it 'it) x form)
        (list form x))
    `(--> (--> ,x ,form) ,@more)))

(put '-> 'lisp-indent-function 1)
(put '->> 'lisp-indent-function 1)
(put '--> 'lisp-indent-function 1)

(defmacro -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."
  (let ((var (car var-val))
        (val (cadr var-val)))
    `(let ((,var ,val))
       (when ,var
         ,@body))))

(defmacro -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*')."
  (if (= (length vars-vals) 1)
      `(-when-let ,(car vars-vals)
         ,@body)
    `(-when-let ,(car vars-vals)
       (-when-let* ,(cdr vars-vals)
         ,@body))))

(defmacro --when-let (val &rest body)
  "If VAL evaluates to non-nil, bind it to `it' and execute
body."
  `(let ((it ,val))
     (when it
       ,@body)))

(defmacro -if-let (var-val then &optional else)
  "If VAL evaluates to non-nil, bind it to VAR and do THEN,
otherwise do ELSE. VAR-VAL should be a (VAR VAL) pair."
  (let ((var (car var-val))
        (val (cadr var-val)))
    `(let ((,var ,val))
       (if ,var ,then ,else))))

(defmacro -if-let* (vars-vals then &optional else)
  "If all VALS evaluate to true, bind them to their corresponding
  VARS and do THEN, otherwise do ELSE. VARS-VALS should be a list
  of (VAR VAL) pairs (corresponding to the bindings of `let*')."
  (let ((first-pair (car vars-vals))
        (rest (cdr vars-vals)))
    (if (= (length vars-vals) 1)
        `(-if-let ,first-pair ,then ,else)
      `(-if-let ,first-pair
         (-if-let* ,rest ,then ,else)
         ,else))))

(defmacro --if-let (val then &optional else)
  "If VAL evaluates to non-nil, bind it to `it' and do THEN,
otherwise do ELSE."
  `(let ((it ,val))
     (if it ,then ,else)))

(put '-when-let 'lisp-indent-function 1)
(put '-when-let* 'lisp-indent-function 1)
(put '--when-let 'lisp-indent-function 1)
(put '-if-let 'lisp-indent-function 1)
(put '-if-let* 'lisp-indent-function 1)
(put '--if-let 'lisp-indent-function 1)

(defun -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'"
  (let (result)
    (--each list (unless (-contains? result it) (!cons it result)))
    (nreverse result)))

(defun -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."
  (let (result)
    (--each list (!cons it result))
    (--each list2 (unless (-contains? result it) (!cons it result)))
    (nreverse result)))

(defalias '-uniq '-distinct)

(defun -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."
  (--filter (-contains? list2 it) list))

(defun -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."
  (--filter (not (-contains? list2 it)) list))

(defvar -compare-fn nil
  "Tests for equality use this function or `equal' if this is nil.
It should only be set using dynamic scope with a let, like:
(let ((-compare-fn =)) (-union numbers1 numbers2 numbers3)")

(defun -contains? (list element)
  "Return whether LIST contains ELEMENT.
The test for equality is done with `equal',
or with `-compare-fn' if that's non-nil."
  (not
   (null
    (cond
     ((null -compare-fn)    (member element list))
     ((eq -compare-fn 'eq)  (memq element list))
     ((eq -compare-fn 'eql) (memql element list))
     (t
      (let ((lst list))
        (while (and lst
                    (not (funcall -compare-fn element (car lst))))
          (setq lst (cdr lst)))
        lst))))))

(defalias '-contains-p '-contains?)

(defun -sort (predicate list)
  "Sort LIST, stably, comparing elements using PREDICATE.
Returns the sorted list.  LIST is NOT modified by side effects.
PREDICATE is called with two elements of LIST, and should return non-nil
if the first element should sort before the second."
  (sort (copy-sequence list) predicate))

(defmacro --sort (form list)
  "Anaphoric form of `-sort'."
  (declare (debug t))
  `(-sort (lambda (it other) ,form) ,list))

(defun -repeat (n x)
  "Return a list with X repeated N times.
Returns nil if N is less than 1."
  (let (ret)
    (--dotimes n (!cons x ret))
    ret))

(defun -sum (list)
  "Return the sum of LIST."
  (apply '+ list))

(defun -product (list)
  "Return the product of LIST."
  (apply '* list))

(defun -min (x &rest xs)
  "Return the smallest value of all arguments."
  (apply 'min (cons x xs)))

(defun -min-by (pred list)
  "Call PRED for each item in LIST and return item with smallest value."
  (let (min-item (min-value most-positive-fixnum))
    (-each
     list
     (lambda (item)
       (let ((item-value (funcall pred item)))
         (when (< item-value min-value)
           (setq min-value item-value)
           (setq min-item item)))))
    min-item))

(defmacro --min-by (form list)
  "Anaphoric form of `-min-by'."
  (declare (debug t))
  `(-min-by (lambda (it) ,form) ,list))

(defun -max (x &rest xs)
  "Return the largest value of all arguments."
  (apply 'max (cons x xs)))

(defun -max-by (pred list)
  "Call PRED for each item in LIST and return item with largest value."
  (let (max-item (max-value most-negative-fixnum))
    (-each
     list
     (lambda (item)
       (let ((item-value (funcall pred item)))
         (when (> item-value max-value)
           (setq max-value item-value)
           (setq max-item item)))))
    max-item))

(defmacro --max-by (form list)
  "Anaphoric form of `-max-by'."
  (declare (debug t))
  `(-max-by (lambda (it) ,form) ,list))

(eval-after-load "lisp-mode"
  '(progn
     (let ((new-keywords '(
                           "--each"
                           "-each"
                           "--each-while"
                           "-each-while"
                           "--dotimes"
                           "-dotimes"
                           "-map"
                           "--map"
                           "--reduce-from"
                           "-reduce-from"
                           "--reduce"
                           "-reduce"
                           "--reduce-r-from"
                           "-reduce-r-from"
                           "--reduce-r"
                           "-reduce-r"
                           "--filter"
                           "-filter"
                           "-select"
                           "--select"
                           "--remove"
                           "-remove"
                           "-reject"
                           "--reject"
                           "--keep"
                           "-keep"
                           "-flatten"
                           "-concat"
                           "--mapcat"
                           "-mapcat"
                           "--first"
                           "-first"
                           "--any?"
                           "-any?"
                           "-some?"
                           "--some?"
                           "-any-p"
                           "--any-p"
                           "-some-p"
                           "--some-p"
                           "--all?"
                           "-all?"
                           "-every?"
                           "--every?"
                           "-all-p"
                           "--all-p"
                           "-every-p"
                           "--every-p"
                           "--none?"
                           "-none?"
                           "-none-p"
                           "--none-p"
                           "-only-some?"
                           "--only-some?"
                           "-only-some-p"
                           "--only-some-p"
                           "-take"
                           "-drop"
                           "--take-while"
                           "-take-while"
                           "--drop-while"
                           "-drop-while"
                           "-split-at"
                           "-insert-at"
                           "--split-with"
                           "-split-with"
                           "-partition"
                           "-partition-in-steps"
                           "-partition-all"
                           "-partition-all-in-steps"
                           "-interpose"
                           "-interleave"
                           "--zip-with"
                           "-zip-with"
                           "-zip"
                           "--map-indexed"
                           "-map-indexed"
                           "--map-when"
                           "-map-when"
                           "--replace-where"
                           "-replace-where"
                           "-partial"
                           "-rpartial"
                           "-juxt"
                           "->"
                           "->>"
                           "-->"
                           "-when-let"
                           "-when-let*"
                           "--when-let"
                           "-if-let"
                           "-if-let*"
                           "--if-let"
                           "-distinct"
                           "-intersection"
                           "-difference"
                           "-contains?"
                           "-contains-p"
                           "-repeat"
                           "-cons*"
                           "-sum"
                           "-product"
                           "-min"
                           "-min-by"
                           "--min-by"
                           "-max"
                           "-max-by"
                           "--max-by"
                           ))
           (special-variables '(
                                "it"
                                "it-index"
                                "acc"
                                "other"
                                )))
       (font-lock-add-keywords 'emacs-lisp-mode `((,(concat "\\<" (regexp-opt special-variables 'paren) "\\>")
                                                   1 font-lock-variable-name-face)) 'append)
       (font-lock-add-keywords 'emacs-lisp-mode `((,(concat "(\\s-*" (regexp-opt new-keywords 'paren) "\\>")
                                                   1 font-lock-keyword-face)) 'append))
     (--each (buffer-list)
       (with-current-buffer it
         (when (and (eq major-mode 'emacs-lisp-mode)
                    (boundp 'font-lock-mode)
                    font-lock-mode)
           (font-lock-refresh-defaults))))))

(provide 'dash)
;;; dash.el ends here