Lisp for Python Programmers

Lisp for Python Developers

Vsevolod Dyomkin
@vseloved
2013-01-26

Topics

* A short intro
* Some myths and facts
* What Lisp offers

Hello World
CL-USER> "Hello world"
"Hello world"

CL-USER> (print "Hello world")

"Hello world"
"Hello world"

Horner's Rule
(Is Lisp a functional language?)

(defun horner (coeffs x)
(reduce (lambda (coef acc)
(+ (* acc x) coef))
coeffs
:from-end t
:initial-value 0))

From Rosetta Code:
http://rosettacode.org/wiki/Horner%27s_rule_for_polynomial_evaluation

Horner's Rule
(Python version)

def horner(coeffs, x):
return reduce(lambda acc, c:
acc * x + c,
reversed(coeffs),
0)

Lisp Tools

1. Implementations - multiple
2. IDEs - SLIME, SLIMV
3. quicklisp

Myths
* The syntax myth
* The libraries myth
* The community myth
* The slowness myth
* The outdatedness myth
* The myth of too much choice
* The myth of academic language

Myth | Fact
LISP = Lost In )))))))])))))])]) —
Stupid Parenthesis the joy of debugging
ASTs
Your eyes are gonna
-- Armin Ronacher
bleed!!!! (https://twitter.com/mitsuhi
ko/status/88527153158815744)

Myth | Fact
There are no Lisp 1961 libraries in
libraries Quicklisp

Myth | Fact
There are no Lisp 1961 libraries in
libraries Quicklisp

27413 libraries in
PyPI

(defun graylog (message &key level backtrace file line-no)
(let (sock)
(unwind-protect
(let ((msg (salza2:compress-data
(babel:string-to-octets
(json:encode-json-to-string
#{:version "1.0" :facility "lisp"
:host (get-hostname)
:|short_message| message
:|full_message| backtrace
:timestamp (local-time:timestamp-to-unix
(local-time:now))
:level level :file file :line line-no
})
:encoding :utf-8)
'salza2:zlib-compressor)))
(setf sock (usocket:socket-connect *graylog-host*
*graylog-port*
:protocol :datagram
:element-type 'ub8))
(usocket:socket-send sock msg (length msg))))
(usocket:socket-close sock)))

Myth | Fact
There's no Lisp SBCL – more than 10
programmers people contribute to
each release, ABCL –
There's no Lisp more than 5, etc.
jobs
This year: 2 Lisp
Lisp community is conferences in Europe
full of trolls for up to 100 people
(ECLM & ECLS) &
Lisp hasn't been numerous Lisp user
developed for years groups meetings

http://lisp-univ-etc.blogspot.com/search/label/lisp-hackers

Myth | Fact
Lisp is slow Lisp is the fastest
of popular dynamic
languages

Lisp can be faster
than Java

… or even C

http://benchmarksgame.
alioth.debian.org/u32q
/lisp.php

Cool Lisp Features
1. Macros
2. All the functional stuff
3. CLOS multimethods
4. Special variables
5. Condition system
6. Read macros
7. The richest calling convention
8. Etc.

Macros

This page is intentionally left blank

Condition system
Jedis redis = Redis.getClient(Redis.SOME_DB);
try {
while (!Thread.interrupted())
try {
// do some useful work
break;
} catch (JedisException e) {
Redis.returnBrokenClient(redis);
redis = Redis.getClient(Redis.SOME_DB);
}
// do some other stuff
} finally {
Redis.returnClient(redis);
}

Condition system
(with-persistent-connection (host port)
;; do useful stuff
)

Condition system
(with-persistent-connection (host port)
;; do useful stuff
)

(defmacro with-persistent-connection
((&key (host #(127 0 0 1)) (port 6379))
&body body)
`(with-connection (:host ,host :port ,port)
(handler-bind ((redis-connection-error
(lambda (e)
(warn "Reconnecting.")
(invoke-restart :reconnect))))
,@body)))

Condition system
(defmacro with-reconnect-restart (&body body)
`(handler-case (progn ,@body)
(usocket:connection-refused-error (e)
(reconnect-restart-case
(:error e :comment "Can't connect”)
,@body))
((or usocket:socket-error
stream-error end-of-file) (e)
(reconnect-restart-case (:error e)
,@body)))))

Condition system
(defmacro reconnect-restart-case
((&key error comment) &body body)
`(if *pipelined*
(progn ,@body)
(restart-case (error 'redis-connection-error
:error ,error
:comment ,comment)
(:reconnect ()
:report "Trying to reconnect"
(reconnect)
,@body))))

http://lisp-univ-etc.blogspot.com/2012/11/cl-redis-separation-
of-concerns-in.html

Read macros
{ x ! x <- (loop :for i :upto 10 :collect i) }
'(0 1 2 3 4 5 6 7 8 9 10 )

{x ! x <- '(1 nil 2) ! x}
'(1 2)

{x y ! x <- '(1 2 3) y <- '(5 6 7) ! (oddp x) (> y 5)}
'((3 7))

{ (+ x y) ! x <- '(1 2 3) y <- '(5 6 7) ! (oddp x) (> y 5) }
'(10)

(set-macro-character #{ #'read-listcomp)
(set-macro-character #} (get-macro-character #)))

(defun read-listcomp (stream char)
"Read list comprehension { vars ! generators [! conditions]? }"
(declare (ignore char))
(let (rezs srcs conds state)
(dolist (item (read-delimited-list #} stream))
(if (eql '! item)
(setf state (if state :cond :src))
(case state
(:src (push item srcs))
(:cond (push item conds))
(otherwise (push item rezs)))))
(setf rezs (reverse rezs)
srcs (reverse srcs)
conds (reverse conds))
(let ((binds (mapcar #`(cons (first %) (third %))
(group 3 srcs))))
`(mapcan (lambda ,(mapcar #'car binds)
(when (and ,@conds)
(list ,(if (rest rezs)
(cons 'list rezs)
(first rezs)))))
,@(mapcar #'cdr binds)))))

Lisp is Python on
steroids

but w/o
batteries :)

Lisp in My View
1. Rich, non-exclusive culture
2. Consistency & simplicity
3. Mature interactive environment
4. Multi-paradigm language
5. Unique features
6. Cool non-unique features
7. Performant grown-up runtimes

Lisp Resources
1. Hyperspec -
http://clhs.lisp.se/Front/Contents.htm
2. Cookbook -
http://cl-cookbook.sourceforge.net/
3. Cliki – http://cliki.net
4. lispdoc - http://lispdoc.com/
5. Google Styleguide -
http://google-styleguide.googlecode.com/svn/trunk/lispguide.xml

6. L1sp.org - http://l1sp.org/
7. Lisp books -
http://pinterest.com/vseloved/lisp-books/

Lisp for Python Programmers

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