bang.el

The startings of a modern list api for Emacs. Does not require 'cl.

We're looking to Clojure for naming and signatures.

Warning

This is so much a work in progress that you should definitely not be using it yet.

Functions

• !map (fn list)
• !reduce-from (fn initial-value list)
• !reduce (fn list)
• !filter (fn list)
• !remove (fn list)
• !keep (fn list)
• !concat (&rest lists)
• !mapcat (fn list)
• !partial (fn &rest args)
• !difference (list list2)
• !intersection (list list2)
• !distinct (list)
• !contains? (list element)

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

Anaphoric functions

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

(!filter (lambda (num) (= 0 (% num 2))) '(1 2 3 4)) ;; normal version

(!!filter (= 0 (% it 2)) '(1 2 3 4)) ;; anaphoric version

of course the original can also be written like

(defun even? (num) (= 0 (% num 2)))

(!filter even? '(1 2 3 4))

which demonstrates the usefulness of both versions.

Documentation and examples

!map (fn list)

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

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

!reduce-from (fn initial-value list)

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

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

(!reduce-from '+ 7 '(1 2)) ;; => 10
(!reduce-from (lambda (memo item) (+ memo item)) 7 '(1 2)) ;; => 10
(!!reduce-from (+ acc it) 7 '(1 2 3)) ;; => 13

!reduce (fn list)

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

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

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

!filter (fn list)

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

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

!remove (fn list)

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

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

!keep (fn list)

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

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

!concat (&rest lists)

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

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

!mapcat (fn list)

Returns the result of applying concat to the result of applying map to fn and list. Thus function fn should return a collection.

(!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)

!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 + additional args.

(funcall (!partial '+ 5) 3) ;; => 8
(funcall (!partial '+ 5 2) 3) ;; => 10

!difference (list list2)

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

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

!intersection (list list2)

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

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

!distinct (list)

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

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

!contains? (list element)

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

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

Development

Run the tests with

./run-tests.sh

Create the docs with

./create-docs.sh

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

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

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

License

Copyright (C) 2012 Magnar Sveen, Joel McCracken

Authors: Magnar Sveen magnars@gmail.com Joel McCracken 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/.