Dao is an object-oriented scripting language with dynamic-typing variables supporting complex data structures. It has powerful text processing ability such as string regular expression matching. It provides built-in numerical data types such as complex number and multi-dimensional numeric array, and their corresponding, convenient operations and computations. Supporting for multi-threaded programming is also implemented as an integrated part of Dao. The inerpreter of this language is implemented as a light-weighted and efficient virtual register machine (Dao VM) in standard C. The Dao VM can be easily extended with C/C++, through a simple and transparent interface. It can also be easily embedded into other C/C++ programs. A programming paradigm is a paradigmatic style of programming (compare with a methodology, which is a paradigmatic style of doing software engineering). ... This does not cite any references or sources. ... A software release refers to the creation and availability of a new version of a computer software product. ... C++ (pronounced see plus plus, IPA: ) is a general-purpose programming language with high-level and low-level capabilities. ... In computing, the Lua (pronounced LOO-ah, or in IPA) programming language is a lightweight, reflective, imperative and procedural language, designed as a scripting language with extensible semantics as a primary goal. ... Python is an interpreted, interactive programming language created by Guido van Rossum in 1990, originally as a scripting language for Amoeba OS capable of making system calls. ... Wikibooks has a book on the topic of Perl Programming Perl is a dynamic programming language created by Larry Wall and first released in 1987. ... // An operating system (OS) is the software that manages the sharing of the resources of a computer. ... A cross-platform (or platform independent) programming language, software application or hardware device works on more than one system platform (e. ... A software license is a legal agreement which may take the form of a proprietary or gratuitous license as well as a memorandum of contract between a producer and a user of computer software. ... GNU logo The GNU Lesser General Public License (formerly the GNU Library General Public License) is an FSF approved Free Software license designed as a compromise between the GNU General Public License and simple permissive licenses such as the BSD license and the MIT License. ... A website (alternatively, Web site or web site) is a collection of Web pages, images, videos and other digital assets that is hosted on one or several Web server(s), usually accessible via the Internet, cell phone or a LAN. A Web page is a document, typically written in HTML... Object-oriented programming (OOP) is a computer programming paradigm in which a software system is modeled as a set of objects that interact with each other. ... Scripting languages (commonly called scripting programming languages or script languages) are computer programming languages that are typically interpreted and can be typed directly from a keyboard. ... A binary tree, a simple type of branching linked data structure. ... In computing, a regular expression is a string that is used to describe or match a set of strings, according to certain syntax rules. ... Many programming languages, operating systems, and other software development environments support what are called threads of execution. ... C is a general-purpose, block structured, procedural, imperative computer programming language developed in 1972 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system. ...

More advanced features of the language includes: mixed static- and dynamic- typing system that allows explicit or implicit type declaration of variables, and is capable of automated data type deduction; a flexible macro system that allows definition of new syntax; conucurrent and distributed programming with message passing interfaces; mixed programming with C language using TCC.

Basics

Hello World

The classic hello world program can be written as follows: A hello world program is a computer program that prints out Hello, World! on a display device. ...

 stdio.print ( "Hello world!" ) 

Here stdio is the standard library to handle input and output. In Dao, there is no builtin functions, which are all part of certain library such as: stdio, stdlib, math, coroutine, reflect, mpi(message passing interface), network, thread etc. The methods in a library, math for example, can be shown by:

 stdlib.listmeth ( math ) 

Data Types

A Dao variable can be declared by assign the result of an expression to a variable name.

 a_number = 123 a_string = "abc" a_list = { 1, 2, 3 } a_hash = { "CD"=>123, "AB"=>456 } a_vector = [ 1, 2, 3 ] a_matrix = [ 1, 2; 3, 4 ] 

By default, a variable will have a fixed type that is inferred from the expression that is used to declare the variable, this is so called implicit typing. The type of a variable can also be specified explicitly as

 var_typed : type var_typed : type = value 

type can be one of the following keywords for built-in types: int, float, double, string, complex, list, hash, array, buffer, routine, and composition of them. type can also be a Dao class name or the name of a user-defined C type. Special keywords/symbols for typing include: any for any types, ? for undefined types and @X for type holder that can be initialized to certain type in parameter list.

For example,

 a_list2 : list<list<float> > a_list3 : list<list<string> > = {} a_hash2 : hash<string,int> = { "ABC"=>123 } 

Typed variables are subjected to compiling time checking for type consistency for operations.

Logic/Looping/Branching Constrols

If-Elif-Else:

 a = math.rand(); if( a > 0.75 ){ a -= 0.75 }elif( a > 0.5 ){ a -= 0.5 }else{ a -= 0.25 } 

While:

 i = 0; while( i < 10 ) i++ 

For:

 for( i=0; i<10; i++ ) stdio.println( i ) for( i=0 : 9 ) stdio.println( i ) for( i=0 : 2 : 9 ) stdio.println( i ) 

For-in:

 a_list = { 1, 2, 3 } for( it in a_list ) stdio.println( it ) a_list2 = { "a", "b", "c" } for( it in a_list; it2 in a_list2 ) stdio.println( it, it2 ) 

For-in also works for hash.

Switch

 a = "abc" switch( a ){ case 1 : a += 123; case "abc" : a += "456" default : stdio.println( "default case" ) } 

Routine(Function)

 routine foo( a, b : string, c = 123 ) => int { return 456; } 

Dao supports high order functions. The definition of such functions is identical to the normal function definition, except the following difference: (1), there is no need for a function name, but the created function must be assigned to a variable; (2), the default value expressions do not necessary to be constant expressions, they are evaluated at running time when the function is created; (3), the function body may contain variables defined in the "upper" function that creates it.

 a = "ABC"; rout = routine( x, y : string, z = a+a ){ a += "_abc"; stdio.println( "lambda ", a ) stdio.println( "lambda ", y ) stdio.println( "lambda ", z ) } rout( 1, "XXX" ); 

Class

 class MyNumber( value = 0 ) { private my Value = 0; # default value is zero Value = value; public routine setValue( value : int ){ Value = value } routine getValue(){ return Value } } 

Macro

In Dao macros are defined in the following way, the syntax patterns are written in BNF-like representation:

 syntax{ source_syntax_pattern }as{ target_syntax_pattern } 

The following syntax will support "while-do-end" without brackets,

 syntax{ while $EXP do [ $BL ] end }as{ while( $EXP ){ [ $BL ] } } 

Concurrent and Distributed Programming

Asynchronous Function Call

Probably, the simplest way to create multi-threaded programs in Dao is to use asynchronous function calls (AFC). The way of using AFC is almost identical to that of normal function calls, with the exception that the keyword async must follow the call.

 myfunc( myparams ) async; myobj.mymeth( myparams ) async; 

Any functions or methods can be invoked in such asynchronous way.

Normally AFC is executed in a separated native thread, which can be either an idle thread available from the thread pool, or a new thread created on the fly.

Message Passing Interface

With Message Passing Interface APIs provided in library mpi, one can easily do concurrent and distributed programming in Dao. In the MPI library, there are 3 principle functions: spawn(), send() and receive(). With spawn(), one can create lightweighted virtual machine processes or real operation system processes, in the local or remove computers; and with send() and receive(), a process can send message to or receive message from other process.

The process names are of the following form:

 virtual_process@real_process@@hostname 

"@real_process@@hostname" identifies an operating system process on host "@@hostname", and "virtual_process@real_process@@hostname" identifies a virtual process within "@real_process@@hostname". Message passing can only happen among virtual processes. Each real process has a main virtual process named "self". Any part can be omitted. For example, when "virtual_process" is omitted, it means the "self" virtual process, and "@@hostname" alone identifies the "self" within the operating system process that binds to port 4115 ( D : 4, A : 1, O : 15 ).

 # spawn a real process to run script "mpi_script.dao" mpi.spawn( "@pid", "mpi_script.dao" ); # spawn a virtual process to run function "test" mpi.spawn( "vmp@pid", "test" ); 

 # send message to a real process mpi.send( "@pid", "TO MAIN" ); 

 # print a received message stdio.println( mpi.receive() ); 

 # spawn a real process on "@@localhost" to run script "mpi_script.dao" mpi.spawn( "@pid2@@localhost", "mpi_script.dao" ); # spawn a virtual process on "@pid2@@localhost" to run function "test" mpi.spawn( "vmp@pid2@@localhost", "test" ); # send message to the virtual process "vmp@pid2@@localhost" mpi.send( "vmp@pid2@@localhost", "ANOTHER", 123.456 );b 

External links

• Dao Language
• Daoscript