====== Using ECL (Embeddable Common-Lisp) on SDF ======

==== Contents: ====

  * [[#what|What is ECL?]]
  * [[#compare|ECL vs CLISP]]
  * [[#basics|ECL Basics]]
  * [[#oneliners|ECL one-liners]]
  * [[#asdf|ASDF]]
  * [[#customize|Customizations]]
  * [[#refs|References]]

===== What is ECL? =====

ECL stands for //Embeddable Common-Lisp// and is a free open source ANSI Common-Lisp implementation. Its distinguishing attributes are maintaining a small-footprint, and being embeddable with existing C/C++ applications. ECL is LGPL licensed and hosted at [[http://ecls.sourceforge.net/|ecls.sourceforge.net]].

ECL-11.1.1 is currently available to MetaARPA members on most SDF hosts.

===== ECL vs CLISP =====

There are currently two Common-Lisp implementations available on SDF; ECL and CLISP. Both are largely compliant with the ANSI Common-Lisp standard. Each supports various object systems, debugging, bytecode compiling, unicode, sockets, streams, etc. CLISP comes with built-in readline support; ECL doesn't, though it can be added; see the [[#asdf|ASDF]] section. In addition to being smaller and faster than CLISP, ECL can be embedded in C/C++ programs, allow embedded C/C++ code in Lisp programs, and produce stand-alone ELF executables. ECL is also very well documented.

===== ECL Basics =====

By default ECL starts up in interactive mode. Log into SDF host //miku// and type "'ecl'"; you should see something like below:

  ECL (Embeddable Common-Lisp) 11.1.1
  Copyright (C) 1984 Taiichi Yuasa and Masami Hagiya
  Copyright (C) 1993 Giuseppe Attardi
  Copyright (C) 2000 Juan J. Garcia-Ripoll
  ECL is free software, and you are welcome to redistribute it
  under certain conditions; see file 'Copyright' for details.
  Type :h for Help.
  Top level.
  >

The default ECL prompt is ">". Enter Common-Lisp commands in the usual way:

  > (+ 1 2 3)
  6

  > (* 4 5)
  20

  > (format t "hello SDF~&")
  hello SDF
  NIL
  >

In-line help is available ; type :h for options. The debugger can be entered using "(break)" ; once entered typed :h to see options. To exit the ECL interactive session type ":exit" .

===== ECL one-liners =====

To use ECL as a script executor (ie. CGI) the //-shell// and/or //-eval// options can be used. The //-norc// is often a good addition so as to avoid unnecessary loading of modules, etc.

ex: hello.lsp

  % echo '(format t "~&Hello SDF~&")' > hello.lsp

  % ecl -norc -script hello.lsp
  Hello SDF

It's also possible to use ECL to execute simple Common-Lisp one-liners at the command line (note that //princ// is needed for screen output):

  % ecl -norc -shell /dev/null -eval "(princ (* 1 2 3))"
  6

A nicer way to accomplish the same is to create a small shell script:

  #!/bin/sh
  # lispit - executes a lisp expression and dumps it to stdout

  LSP_EXPR=${@}

  if [ "$#" -eq 0 ]; then
          echo "lispit - executes a lisp expression"
          echo "  usage: lispit '(lisp_expression)'"
          echo ""
          exit 1
  fi

  ecl -norc -shell /dev/null -eval "(princ ${LSP_EXPR} )"
  echo ""
  exit 0

Example run:

  % lispit '(mapcar (lambda (x) (expt x 2)) `(1 2 3 4 5))'
  (1 4 9 16 25)

===== ASDF / enabling readline =====

ASDF (//Another System Definition Facility//) is an extensible build facility for Common-Lisp software. ECL comes with ASDF bundled in, however on SDF, users must setup their own ASDF repository under their $HOME directory.

The following outlines the process, using the //ecl-readline// module (adds GNU readline support to ECL) as example:

1) Create the user-level ASDF repository:

  % mkdir -p $HOME/LISP/ASDF

2) Create the ASDF config directory and config file*:

  % cd $HOME
  % mkdir -p .config/common-lisp/source-registry.conf.d
  % vi .config/common-lisp/source-registry.conf.d/asdf.conf

  # ../asdf.conf
  ;;additional directory for ASDF to search (no recursion):
  (:directory "/LISP/ASDF/")

*note: you can call the conf file anything you want.

3) Download ecl-readline module and copy select files to $HOME/LISP/ASDF:

  % cd /tmp
  % snarf http://www.common-lisp.net/project/ecl-readline/releases/ecl-readline-0.4.1.tar.gz
  % tar xzf ecl-readline-0.4.1.tar.gz
  % cd ecl-readline-0.4.1/
  % cp ecl-*.* $HOME/LISP/ASDF/

4) Create the ECL startup file:

  # $HOME/.eclrc
  (require 'asdf)
  (asdf:operate 'asdf:load-op 'ecl-readline)
  (ecl-readline::enable)

The next time you startup ECL it will compile the ecl-readline module and launch an interactive session. With ecl-readline enabled the default ECL prompt is "//CL-USER[n]>//" and you should then be able to use Emacs-style command editing and history recall. If you don't like the provided prompt you can change it by editing the //ecl-readline.lisp// file.

===== Customizations =====

Additional modifications can be made to the ECL startup file, such as user-defined functions and tweaks to various modules. Below is a more nuanced example which reduces the verbosity at startup, modifies ecl-readline's history file location, and adds an external SHELL function similar to that found in CLISP:

  # $HOME/.eclrc
  (require 'asdf)
  (setf ASDF:*ASDF-VERBOSE* nil) ; quiets ASDF output some
  (setf *load-verbose* nil)       ; quiets the LOAD process some
  (asdf:operate 'asdf:load-op 'ecl-readline)
  (ecl-readline::enable :history-file "/var/tmp/.ecl-history")
  ;;
  ;; customizations

  ;; GNU clisp-like SHELL cmd
  (defun shell (&optional (shell_cmd "$SHELL"))
  "Args: (&optional shell_cmd)
  SHELL calls the EXT:SYSTEM function. Executes SHELL_CMD if given, otherwise
  User sub-shell is spawned. SHELL_CMD be string or symbol, 256 characters max."
     (ext:system shell_cmd))

===== References: =====

  * //ecl(1)// and //ecl-config(1)// manpages
  * http://ecls.sourceforge.net/
  * [[http://common-lisp.net/project/asdf/|http://common-lisp.net/project/asdf]]
  * [[http://common-lisp.net/project/ecl-readline/|http://common-lisp.net/project/ecl-readline]]
  * [[http://www.cliki.net/Getting%20Started|Getting Started with Common-Lisp]]

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$Id: ecl_tutorial.html,v 1.4 2011/12/12 18:10:28 jgw Exp $