thodg/slides/railsonlisp/index.md

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Rails On Lisp

Thomas de Grivel thoxdg@gmail.com

https://kmx.io/

2020-03-11

Common Lisp

Introduction

Common Lisp

Common Lisp is the programmable programming language.

Lisp essays by Paul Graham http://www.paulgraham.com/lisp.html

Standardised in 1994 by ANSI

Common Lisp the Language, 2nd Edition https://www.cs.cmu.edu/Groups/AI/html/cltl/cltl2.html

Common Lisp Hyperspec http://www.lispworks.com/documentation/HyperSpec/Front/

http://cliki.net

Common Lisp

Several compilers implement the ANSI standard :

Installation

Install SBCL

Ubuntu :

  sudo apt-get install sbcl

MacOS X :

  brew install sbcl

Install repo

mkdir -p ~/common-lisp/thodg
cd ~/common-lisp/thodg
git clone https://github.com/thodg/repo.git
cd ~/common-lisp
ln -s thodg/repo/repo.manifest

Configure SBCL

Edit ~/.sbclrc

  ;; ASDF
  (require :asdf)

  ;; repo
  (load "~/common-lisp/thodg/repo/repo")
  (repo:boot)

Launch SBCL

$ sbcl
This is SBCL 1.5.3, an implementation of ANSI Common Lisp.
More information about SBCL is available at <http://www.sbcl.org/>.

SBCL is free software, provided as is, with absolutely no warranty.
It is mostly in the public domain; some portions are provided under
BSD-style licenses.  See the CREDITS and COPYING files in the
distribution for more information.

* _

Install Slime

* (repo:install :slime)

$ /usr/bin/git -C /home/dx/common-lisp/slime clone https://github.com/slime/slime.git
Cloning into 'slime'...

Configure emacs

Edit ~/.emacs

  ;; Common Lisp
  (add-to-list 'load-path "~/common-lisp/slime/slime/")
  (require 'slime-autoloads)
  (add-to-list 'slime-contribs 'slime-fancy)
  (setq inferior-lisp-program
        "sbcl")
  (setq slime-net-coding-system
        'utf-8-unix)

Demo

Launch emacs and slime

$ emacs

M-x slime

CL-USER> _

The REPL

REPL : read, eval, print loop

  (loop
    ;; setup REPL vars
    ;; handle errors, interactive debugger
    (print
      (eval
        (read)))
    (force-output)) ;; flush output buffers

Symbols

A symbol compares faster than a string (pointers comparison).

To get a symbol through eval we have to quote it, with a single quote prefix.

  ;; SLIME
  CL-USER> 'hello-world
  
  HELLO WORLD
  CL-USER> (quote hello-world)     ; equivalent sans syntaxe
  
  HELLO WORLD

http://www.gigamonkeys.com/book/programming-in-the-large-packages-and-symbols.html

Symbols

If the symbol is not quoted then we end up in the interactive debugger :

  ;; SLIME
  CL-USER> hello-world

  The variable HELLO-WORLD is unbound.
     [Condition of type UNBOUND-VARIABLE]

  Restarts:
   0: [CONTINUE] Retry using HELLO-WORLD.
   1: [USE-VALUE] Use specified value.
   2: [STORE-VALUE] Set specified value and use it.
   3: [RETRY] Retry SLIME REPL evaluation request.
   4: [*ABORT] Return to SLIME's top level.

  Backtrace:
    0: (SB-INT:SIMPLE-EVAL-IN-LEXENV HELLO-WORLD #<NULL-LEXENV>)
    1: (EVAL HELLO-WORLD)
   --more--

  4
  ; Evaluation aborted on #<UNBOUND-VARIABLE HELLO-WORLD {1004AF3523}>.
  CL-USER> _

Functions

defun defines a function.

If the first element of a list (between parentheses) is a function or a symbol naming a function then the list is treated as a function call.

  ;; SLIME
  CL-USER> (defun hello-world ()
             (format t "Hello world !"))
  HELLO-WORLD
  CL-USER> (hello-world)
  Hello world !
  NIL
  CL-USER> _

Lambda

lambda introduces an anonymous function. We can affect an anonymous function to a symbol, not unlike defun.

  ;; SLIME
  CL-USER> (setf (symbol-function 'hello-world)
                 (lambda ()
                   (format t "Hello world !")))

  CL-USER> (hello-world)
  Hello world !
  NIL
  CL-USER> _

Higher order functions

A function is a value like others and can be passed to another function.

We call these functions higher order.

  ;; SLIME
  CL-USER> (mapcar (lambda (x) (* x x)) '(1 2 3 4 5))
  (1 4 9 16 25)
  CL-USER> (reduce #'+ '(1 2 3 4 5))
  15
  CL-USER> (reduce (function +) '(1 2 3 4 5)) ; equivalent to above
  15
  CL-USER> (reduce '+ '(1 2 3 4 5)) ; not equivalent will resolve
                                    ; function at run-time
  15
  CL-USER> _

Macros

  ;; SLIME
  CL-USER> (defmacro hello (arg)
             `(format nil "Hello ~A !"
                (string-capitalize ',arg)))
  HELLO
  CL-USER> (hello world)
  "Hello World !"
  CL-USER> (hello pony)
  "Hello Pony !"
  CL-USER> _

On Lisp, Paul Graham http://lib.store.yahoo.net/lib/paulgraham/onlisp.pdf

Quasiquotation

To quote entirely : '(a b c) or (quote (a b c)) -> (a b c)

To quote partially : `(a b ,c) or (list 'a 'b c) -> (a b 123) if c = 123

Backquote stops evaluation and comma reactivates it locally.

  ;; SLIME
  CL-USER> (let ((c 123))
             `(a b ,c))
  (A B 123)

RailsOnLisp

Installation

Clone RailsOnLisp/rol.git

$ mkdir ~/common-lisp/RailsOnLisp
$ cd ~/common-lisp/RailsOnLisp
$ git clone https://github.com/RailsOnLisp/rol.git
Cloning into 'rol' ...

$ _

Configure PATH

Edit ~/.profile

  if [ -d "$HOME/common-lisp/RailsOnLisp/rol/bin" ]; then
      PATH="$HOME/common-lisp/RailsOnLisp/rol/bin:$PATH"
  fi

Install RailsOnLisp

$ . ~/.profile    # source ~/.profile ou launch a new shell
$ rol install
Cloning into 'rol-assets' ...
Cloning into 'rol-files' ...
Cloning into 'rol-log' ...
Cloning into 'rol-server' ...
Cloning into 'rol-skel' ...
Cloning into 'rol-template' ...
Cloning into 'rol-uri' ...

$ ls -l ~/common-lisp/RailsOnLisp/rol

$ _

Demo

rol new

$ rol new test
Creating test
D .
D ./config
F ./config/app.lisp
F ./config/routes.lisp
F ./config/assets.lisp
D ./data
D ./lib
L ./lib/rol -> /home/dx/common-lisp/RailsOnLisp/rol
F ./Makefile
D ./app
D ./app/assets
D ./app/assets/css
F ./app/assets/css/app.css
D ./app/assets/js
F ./app/assets/js/app.js
D ./app/views
D ./app/views/_layouts
[...]

$ _

make load

$ cd test
$ make load
env LC_ALL=en_US.UTF-8 sbcl --disable-ldb --lose-on-corruption \
 --dynamic-space-size 512 --noinform --end-runtime-options \
 --eval '(declaim (optimize (debug 2) (safety 2) (speed 3) (space 1)))' \
 --disable-debugger \
 --load load.lisp \
 --eval '(run)' \
 --quit

[...]

INFO setup environment development
DEBUG tags: ASSETS APP REPLY MIME FILE DIRECTORY THOT
INFO saving facts into "data/test.facts"
INFO starting thot at 0.0.0.0:4000

INFO Thot start 0.0.0.0:4000
INFO loading mime types from /etc/mime.types
INFO #<FUNCTION THOT::MAIN-LOOP-THREADED>
INFO  #<FUNCTION THOT::ACCEPTOR-LOOP-EPOLL>

localhost:4000

localhost:4000


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