Lisaac

Lisaac

Paradigm	object-oriented prototype-based
Designed by	Benoît Sonntag
Developer	Benoît Sonntag & Jérôme Boutet
First appeared	2003 (2003)
Stable release	0.13.1 (Specification) / February 17, 2008 (2008-02-17)
Typing discipline	static typing
Major implementations
Lisaac
Influenced by
Smalltalk, Self, Eiffel

Lisaac is a statically typed prototype-based language conceived by Benoît Sonntag, in which the Isaac operating system is being written.

The developers of Lisaac also included features such as dynamic inheritance from Self and contract programming from Eiffel. Despite being statically typed, it also shows homoiconic properties. The Lisaac transpiler produces optimized ANSI C code. Compiling results show that it is possible to obtain executables from a high-level prototype-based language that are as fast as C programs.^[1][2]

Features

• Communication protection mechanisms
• Hardware facilities
  • System interrupt support
  • Driver memory mapping
• Despite being compiled, all objects retain their dynamic abilities

Basic syntax

Lisaac is case sensitive. Keywords are capitalized (Section, Header, Public, …), type identifiers are written in upper case letters (INTEGER, BOOLEAN, OBJECT, …), and identifiers denoting variables and slots are written in lower case letters. Objects are composed of slots, which can be data or code. The ':' symbol is used to declare types. Slot names are prefixed with a '+' or '-' symbol to indicate whether the slot is local to an object or shared between objects.

Parentheses are used to delimit lists of semicolon separated statements. Statement lists may have zero, one or more return values. The ':=' symbol is used to bind a slot to a statement or statement list that is executed at the loading/initialization of an object. The '<-' symbol is used to bind a slot to a statement list that is executed on the call of the slot.

Dynamic inheritance

The parent of each object is just a slot that can be assigned as required in the code, for instance:

Section Header

- name := DECOD_MPEG2_TO_SCREEN;

Section Inherit

- videoparent : OBJECT <-
(
  + result : OBJECT;

 typ
 .when 1 then { result := WINDOW;}
 .when 2 then { result := VIDEO_VGA;}
 .when 3 then { result := VIDEO_TVOUT;};

 result
)

Section Public

- typ : INTEGER;

- decode_stream <-

(
 putimage decode_to_bitmap;
)

Operator redefining

In Lisaac, an operator is a slot and can be redefined. For example overloading the + operator for a NUMERIC object:

- '+'  Left 80  other:SELF :SELF <- Self - -other;

Or for a matrix:

- '+'  Left 80  other:SELF :SELF <-

(
	+ result : SELF;

	result := SELF.create count;
	1.to tab.count do {
			i : INTEGER;
		result.put (item i+other.item i) to i;
	};

	result
)

Genericity

Generic objects are supported, for instance:

ARRAY(E), DICTIONARY(KEY,VALUE)

Contract programming

Contract programming using Z notation is provided.

External links

• Lisaac on GNA (moved to Alioth)
• Lisaac on Alioth

Notes and references