EuLisp

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EuLisp
EuLispLogo.png
Paradigm(s) multi-paradigm: functional, procedural, meta, object-oriented
Family Lisp
Appeared in 1990
Preview release 0.991 / 2010
Typing discipline strong, dynamic
Major implementations EuXLisp [1], Youtoo [2], Eu2C [3]
Influenced by Common Lisp InterLisp LeLisp Lisp/VM Scheme T CLOS, ObjVlisp, Oaklisp Dylan
Influenced Dylan, ISLISP
OS Linux
Filename extension(s) .em

EuLisp is a statically and dynamically scoped Lisp dialect developed by a loose formation of industrial and academic Lisp users and developers from around Europe. The standardizers intended to create a new Lisp "less encumbered by the past" (compared to Common Lisp), and not so minimalistic as Scheme. Another objective was to integrate the Object-oriented programming paradigm well.

Origin[edit]

Language definition process first began in a meeting in 1985 in Paris and took a long time. The complete specification and a first implementation (interpreted-only) was available in 1990.

Distinguishing features[edit]

Its primary characteristics are that it is a Lisp-1 (no separate function and variable namespaces), has a CLOS-style (Common Lisp Object System) generic-function type object-oriented system named TELOS (The EuLisp Object System) integrated from the ground up, has a built-in module system, and is defined in layers to promote the use of the Lisp on small, embedded hardware and educational machines. It supports continuations, though not as powerfully as Scheme. It has a simple lightweight process mechanism (threads).

Summary[edit]

Implementations[edit]

An early implementation of EuLisp was FEEL (Free and Eventually Eulisp). The successor to FEEL was Youtoo (interpreted and compiled versions), by University of Bath in the United Kingdom. An interpreter for the basic level of EuLisp, "level-0", was written by Russell Bradford in XScheme, an implementation of Scheme by David Michael Betz, originally called EuScheme but the most recent version is renamed EuXLisp [4] to avoid confusion. Also Eu2C [5], a EuLisp optimizing compiler, was created by Fraunhofer ISST under the APPLY project in Germany [6].

A dialect of EuLisp was developed, called Plural EuLisp; it was EuLisp with parallel programming extensions.

Example[edit]

Example use of classes in the algorithm to solve the "Towers of Hanoi" problem.

(defmodule hanoi
  (syntax (syntax-0)
   import (level-0)
   export (hanoi))
 
;;;-----------------------------------------------------------------------------
;;; Tower definition
;;;-----------------------------------------------------------------------------
(defconstant *max-tower-height* 10)
 
(defclass <tower> ()
  ((id reader: tower-id keyword: id:)
   (blocks accessor: tower-blocks)))
 
(defun build-tower (x n)
  (labels ((loop (i res)
                 (if (= i 0) res
                   (loop (- i 1) (cons i res)))))
          ((setter tower-blocks) x (loop n ()))
          x))
 
(defmethod generic-print ((x <tower>) (s <stream>))
  (sformat s "#<tower ~a: ~a>" (tower-id x) (tower-blocks x)))
 
;;;-----------------------------------------------------------------------------
;;; Access to tower blocks
;;;-----------------------------------------------------------------------------
(defgeneric push (x y))
 
(defmethod push ((x <tower>) (y <fpi>))
  (let ((blocks (tower-blocks x)))
    (if (or (null? blocks) (< y (car blocks)))
        ((setter tower-blocks) x (cons y blocks))
      (error <condition>
             (fmt "cannot push block of size ~a on tower ~a" y x)))))
 
(defgeneric pop (x))
 
(defmethod pop ((x <tower>))
  (let ((blocks (tower-blocks x)))
    (if blocks
        (progn
          ((setter tower-blocks) x (cdr blocks))
          (car blocks))
      (error <condition>
             (fmt "cannot pop block from emtpy tower ~a" x)))))
 
;;;-----------------------------------------------------------------------------
;;; Move n blocks from tower x1 to tower x2 using x3 as buffer
;;;-----------------------------------------------------------------------------
(defgeneric move (n x1 x2 x3))
 
(defmethod move ((n <fpi>) (x1 <tower>) (x2 <tower>) (x3 <tower>))
  (if (= n 1)
      (progn
        (push x2 (pop x1))
        (print x1 nl x2 nl x3 nl nl))
    (progn
      (move (- n 1) x1 x3 x2)
      (move 1 x1 x2 x3)
      (move (- n 1) x3 x2 x1))))
 
;;;-----------------------------------------------------------------------------
;;; Initialize and run the 'Towers of Hanoi'
;;;-----------------------------------------------------------------------------
(defun hanoi ()
  (let ((x1 (make <tower> id: 0))
        (x2 (make <tower> id: 1))
        (x3 (make <tower> id: 2)))
    (build-tower x1 *max-tower-height*)
    (build-tower x2 0)
    (build-tower x3 0)
    (print x1 nl x2 nl x3 nl nl)
    (move *max-tower-height* x1 x2 x3)))
 
(hanoi)
 
;;;-----------------------------------------------------------------------------
)  ;; End of module hanoi
;;;-----------------------------------------------------------------------------

References[edit]

External links[edit]