The GNAT-LLVM project provides an opportunity to port Ada to new platforms, one of which is WebAssembly. We conducted an experiment to evaluate the porting of Ada and the development of bindings to use Web API provided by the browser directly from Ada applications.
Subtotals
As a result of the experiment, the standard language library and runtime library were partially ported. Together with a binding for the Web API, this allowed us to write a simple example showing the possibility of using Ada for developing applications compiled into WebAssembly and executed inside the browser. At the same time, there are some limitations both of WebAssembly and of the current GNAT-LLVM implementation:
- the inability to use tasks and protected types
- support for exceptions limited to local propagation and the last chance handler
- the inability to use nested subprograms
Example
Here is small example of an Ada program that shows/hides the text when pressing the button by manipulating attributes of document nodes.
with Web.DOM.Event_Listeners; with Web.DOM.Events; with Web.HTML.Buttons; with Web.HTML.Elements; with Web.Strings; with Web.Window; package body Demo is function "+" (Item : Wide_Wide_String) return Web.Strings.Web_String renames Web.Strings.To_Web_String; type Listener is limited new Web.DOM.Event_Listeners.Event_Listener with null record; overriding procedure Handle_Event (Self : in out Listener; Event : in out Web.DOM.Events.Event'Class); L : aliased Listener; ------------------ -- Handle_Event -- ------------------ overriding procedure Handle_Event (Self : in out Listener; Event : in out Web.DOM.Events.Event'Class) is X : Web.HTML.Elements.HTML_Element := Web.Window.Document.Get_Element_By_Id (+"toggle_label"); begin X.Set_Hidden (not X.Get_Hidden); end Handle_Event; --------------------- -- Initialize_Demo -- --------------------- procedure Initialize_Demo is B : Web.HTML.Buttons.HTML_Button := Web.Window.Document.Get_Element_By_Id (+"toggle_button").As_HTML_Button; begin B.Add_Event_Listener (+"click", L'Access); B.Set_Disabled (False); end Initialize_Demo; begin Initialize_Demo; end Demo;
As you can see, it uses elaboration, tagged and interface types, and callbacks.
Live demo
Setup & Build
To compile the examples you need to setup GNAT-LLVM & GNAT WASM RTL following instructions in README.md file.
To compile specific example use gprbuild to build application and open index.html in the browser to run it.
Next steps
The source code is published in a repository on GitHub and we invite everyone to participate in the project.
Attachments
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高效能程序员的修炼
[美]Jeff Atwood / 陆其明、张健 / 人民邮电出版社 / 2013-7 / 49
jeff atwood于2004年创办coding horror博客(http://www.codinghorror.com),记录其在软件开发经历中的所思所想、点点滴滴。时至今日,该博客每天都有近10万人次的访问量,读者纷纷参与评论,各种观点与智慧在那里不断激情碰撞。 《高效能程序员的修炼》是coding horror博客中精华文章的集合。全书分为12章,涉及迈入职业门槛、高效能编程、应聘......一起来看看 《高效能程序员的修炼》 这本书的介绍吧!