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Common Lisp for the 21st century |
CL21 is an experimental project redesigning Common Lisp. It makes some common things that were tedious to do much easier and brings some new welcome features:
- more functional programming facilities,
- more object oriented, generic functions.
- new syntax (for regular expressions, hash-tables, string-interpolation,…),
- symbols organized into several packages,
- written in pure Common Lisp.
CL21 is a bit disruptive in the sense that it redefines usual symbols
(specially for the generic functions). Nevertheless, in doubt, you can always use a regular CL symbol by accessing it in the cl:
package. You might want to check
other related projects, that go beyond
Alexandria and stay
"good citizens" of the CL world:
- rutils -
a comprehensive and all-encompassing suite of syntactic utilities to
support modern day-to-day Common Lisp development. It adds readtable
literal syntax for shorter lambdas, hash-tables and vectors
(
#
,…
#h
and#{…}
,#v
), some generic functions (whose name start withgeneric-
), shortcuts for standard operators, and many helpful functions. - Serapeum is a set of utilities
beyond Alexandria, as a supplement. It defines a lot of helper
functions (see its
reference)
for macros, data structures (including more functions for trees,
queues), sequences (
partition
,keep
,…), strings, definitions (defalias
,…),… no new reader macros here.
From http://cl21.org/ :
Dear Common Lispers,
Common Lisp has the most expressive power of any modern language. It has first class functions with lexical closures, an object system with multiple-dispatch and a metaobject protocol, true macros, and more. It is ANSI standardized and has numerous high-performance implementations, many of which are free software.
In spite of this, it has not had much success (at least in Japan). Its community is very small compared to languages like Ruby and most young Lispers are hacking with Clojure.
Why? Common Lisp is much faster than them. Ruby has no macros and even Clojure doesn't have reader macros. Why then?
Because these languges are well-designed and work for most people for most purposes. These languages are easy to use and the speed isn't an issue.
Is Common Lisp sufficiently well-designed? I don't think so. You use different functions to do the same thing to different data types (elt, aref, nth). You have long names for commonly used macros (destructuring-bind, multiple-value-bind). There is no consistency in argument order (getf and gethash). To put it simply, the language is time-consuming to learn.
Given this, how can programmers coming from other languages believe Common Lisp is the most expressive one?
Fortunately in Common Lisp we can improve the interface with abstractions such as functions, macros, and reader macros. If you believe our language is the most expressive and powerful language, then let's justify that belief.
We should consider the future of the language, not only for ourselves but for the next generation.
CL21 is in Quicklisp.
To get its latest version, do:
(ql-dist:install-dist "http://dists.cl21.org/cl21.txt")
(ql:quickload :cl21)
Use:
(in-package :cl21-user)
(defpackage myapp (:use :cl21))
(in-package :myapp)
Please bear in mind that the following is only a summary of CL21 features. To be sure not to miss anything, you should read CL21's wiki, its automated list of major changes from standard CL and better yet, its sources.
That said, go include CL21 in your new project and enjoy, it's worth it !
lm
is a macro for creating an anonymous function:
(lm (x) (typep x 'cons))
;=> #<FUNCTION (LAMBDA (X)) {1008F50DAB}>
(map (lm (x) (+ 2 x)) '(1 2 3))
;=> (3 4 5)
^
is a reader macro which will be expanded to lm
.
^(typep % 'cons)
;=> #<FUNCTION (LAMBDA (%1 &REST #:G1156 &AUX ...)) {10092490CB}>
(map ^(+ 2 %) '(1 2 3))
;=> (3 4 5)
Unused arguments will be ignored automatically.
(map ^(random 10) (iota 10))
;=> (6 9 5 1 3 5 4 0 7 4)
%n
designates the nth argument (1-based). %
is a synonym for %1
.
(sort '(6 9 5 1 3 5 4 0 7 4) ^(< %1 %2))
;=> (0 1 3 4 4 5 5 6 7 9)
function
is a special operator for getting a function value from a given form.
If a symbol is given, function
returns a function value of it.
(function integerp)
;=> #<FUNCTION INTEGERP>
If a form which starts with compose
, and
, or
or not
, function
returns a composed function.
(function (compose - *))
<=> (compose (function -) (function *))
(function (and integerp evenp))
<=> (conjoin (function integerp) (function evenp))
(function (or oddp zerop))
<=> (disjoin (function oddp) (function zerop))
(function (not zerop))
<=> (complement (function zerop))
#'
is a reader macro for function
.
#'(compose - *)
#'(and integerp evenp)
#'(or oddp zerop)
#'(not zerop)
#'(and integerp (or oddp zerop))
CL21 gets new symbols: curry
and rcurry
. See also
functions.
Lazy sequences in CL21 (src) use the new abstract classes (wiki).
(use-package :cl21.lazy)
(defun fib-seq ()
(labels ((rec (a b)
(lazy-sequence (cons a (rec b (+ a b))))))
(rec 0 1)))
(take 20 (fib-seq))
;=> (0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584 4181)
(take 3 (drop-while (lambda (x) (< x 500)) (fib-seq)))
;=> (610 987 1597)
This actually is not included in CL21 but may be worth the addition in this section. For immutable data structures, see the Fset library (in Quicklisp).
There are several generic functions which have the same name to CL's normal functions.
- getf
- equalp
- emptyp
- coerce
(defvar *hash* #H(:name "Eitaro Fukamachi" :living "Japan"))
(getf *hash* :name)
;=> "Eitaro Fukamachi"
(coerce *hash* 'plist)
;=> (:LIVING "Japan" :NAME "Eitaro Fukamachi")
You can define these methods for your own classes.
There are also new functions:
append
flatten
elt
: Returns the element at position INDEX of SEQUENCE or signals a ABSTRACT-METHOD-UNIMPLMENETED error if the sequence method is not implemented for the class of SEQUENCE.emptyp
equalp
split
,split-if
drop
,drop-while
take
,take-while
join
length
keep
,keep-if
,nkeep
,nkeep-if
partition
,partition-if
In Common Lisp, functions which have a name starts with "map" are higher-order functions take a function and a sequence.
It is same to CL21, but in CL21, "map" functions always return a value. This aims to clarify the roles of "iteration" and "mapping".
For that reason, CL21 doesn't have CL's mapc
and mapl
. maphash
exists, but it returns a new hash table.
(maphash (lm (k v)
(cons k (1+ v)))
#H(:a 1 :b 2))
;=> #H(:B 3 :A 2)
map
is similar to Common Lisp's mapcar
except it can take any kind of sequences, not only list.
(map #'- '(1 2 3 4))
;=> (-1 -2 -3 -4)
(map #'- #(1 2 3 4))
;=> #(-1 -2 -3 -4)
CL21 doesn't have mapcar
. Use map
instead.
Filter is provided with keep
, keep-if
(instead of
remove-if[-not]
) and nkeep[-if]
.
Common Lisp has simple iteration facilities: dolist
, dotimes
and dolist
.
In addition, CL21 provides another one: doeach
.
doeach
is similar to dolist
, but it can be used with any kind of sequences and hash-table.
(doeach (x '("al" "bob" "joe"))
(when (> (length x) 2)
(princ #"${x}\n")))
;-> bob
; joe
(doeach ((key value) #H('a 2 'b 3))
(when (> value 2)
(print key)))
;=> B
Destructuring binding form can be placed at the variable position.
(doeach ((x y) '((1 2) (2 3) (3 4)))
(print (+ x y)))
;-> 3
; 5
; 7
CL21 also gets a while
keyword.
New data types were added.
- proper-list
- plist
- alist
- octet
- file-associated-stream
- character-designator
- function-designator
- file-position-designator
- list-designator
- package-designator
- stream-designator
- string-designator
Most of these are imported from trivial-types.
A double quote character is a macro character which represents a string.
"Hello, World!"
;=> "Hello, World!"
A backslash followed by some characters will be treated special.
"Hello\nWorld!"
;=> "Hello
; World!"
#"
is similar to "
, but it allows interpolation within strings.
If ${...}
or @{...}
is seen, it will be replaced by the result value of an expression (or the last expression) inside of it.
#"1 + 1 = ${(+ 1 1)}"
;=> "1 + 1 = 2"
CL21 provides a notation for hash-tables.
#H(:name "Eitaro Fukamachi" :living "Japan")
;=> #H(:LIVING "Japan" :NAME "Eitaro Fukamachi")
Note this always creates a hash-table whose test function is EQUAL
. If you want to create it with another test function, a function hash-table
is also available.
(hash-table 'eq :name "Eitaro Fukamachi")
;=> #H(:NAME "Eitaro Fukamachi")
; instead of
; (defvar *hash* (make-hash-table))
; (setf (gethash :name *hash*) "Eitaro Fukamachi")
Accessing an element is also done with getf
(instead of gethash
):
(getf *hash* :name)
Looping over a hash-table:
(doeach ((key val) *hash*)
(when (< (length key) 2)
(princ #"${x}\n")))
Transform a hash-table into a plist:
(coerce *hash* 'plist)
#(...)
is a notation for vectors. Unlike in Common Lisp, its elements will be evaluated and it creates an adjustable vector.
(let ((a 1)
(b 2)
(c 3))
#(a b c))
;=> #(1 2 3)
(defvar *vec* #(0))
(push 1 *vec*)
;=> #(1 0)
(push-back 3 *vec*)
;=> #(1 0 3)
(pop *vec*)
;=> 1
This new regexp reader macro uses the new "Syntax" extension.
(use-package :cl21.re)
(#/^(\d{4})-(\d{2})-(\d{2})$/ "2014-01-23")
(re-replace #/a/ig "Eitaro Fukamachi" "α")
With run-process
:
(use-package :cl21.process)
(run-process '("ls" "-l" "/Users"))
;-> total 0
; drwxrwxrwt 5 root wheel 170 Nov 1 18:00 Shared
; drwxr-xr-x+ 174 nitro_idiot staff 5916 Mar 5 21:41 nitro_idiot
;=> #<PROCESS /bin/sh -c ls -l /Users (76468) EXITED 0>
or the #`
reader macro:
#`ls -l /Users`
;=> "total 0
; drwxrwxrwt 5 root wheel 170 Nov 1 18:00 Shared
; drwxr-xr-x+ 174 nitro_idiot staff 5916 Mar 5 21:41 nitro_idiot
; "
; ""
; 0
All constant variables were renamed to the name added "+" signs before and after.
+pi+
;=> 3.141592653589793d0
+array-rank-limit+
;=> 65529
CL21 Standard Library is a set of libraries that are distributed with CL21. It is intended to offer a wide range of facilities.
We are working on increasing the number of it. Currently, the following packages are provided.
- cl21.re
- cl21.process
- cl21.os
- cl21.lazy
- cl21.abbr