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Section: New Results

Web programming

Participants : Yoann Couillec, Vincent Prunet, Tamara Rezk, Manuel Serrano [correspondant] .

Hop.js

Multitier programming languages unify within a single formalism and a single execution environment the programming of the different tiers of distributed applications. On the Web, this programming paradigm unifies the client tier, the server tier, and, when one is used, the database tier. This homogenization offers several advantages over traditional Web programming that rely on different languages and different environments for the two or three tiers of the Web application: programmers have only one language to learn, maintenance and evolution are simplified by the use of a single formalism, global static analyses are doable as a single semantics is involved, debugging and other runtime tools are more powerful as they access global informations about the execution [17] .

The three first multitier platforms for the Web all appeared in 2006: GWT (a.k.a., Google Web Toolkit), Links, and Hop [6] , [5] . Each relied on a different programming model and languages. GWT maps the Java programming model on the Web, as it allows, Java/Swing likes programs to be compiled and executed on the Web; Links is functional language with experimental features such as the storing of the whole execution context on the client; Hop is based on the Scheme programming language. These three pioneers have open the path for the other multitier languages such as, Ocsigen for Ocaml, UrWeb, js-scala, etc.

In spite of their interesting properties, multitier languages have not become that popular on the Web. Today, only GWT is widely used in industrial applications but arguably GWT is not a fully multitier language as developing applications with GWT requires explicit JavaScript and HTML programming. This lack of popularity of other systems is likely due to their core based languages than to the programming model itself.

JavaScript is the defacto standard on the Web. Since the mid 90's, it is the language of the client-side programming and more recently, with systems like nodejs, it is also a viable solution for the server-side programming. As we are convinced by the virtues of multitier programming we have started a new project consisting of enabling multitier programming JavaScript. We have created a new language called HopScript, which is a minimalist extension of JavaScript for multitier programming, and we have implemented a brand new runtime environment called Hop.js. This environment contains a builtin Web server, on-the-fly HopScript compilers, and many runtime libraries.

HopScript is a super set of JavaScript, i.e., all JavaScript programs are legal HopScript programs. Hop.js is a compliant JavaScript execution environment as it succeeds at 99% of the Ecma 262 tests suite. The Hop.js environment also aims at Node.js compatibility. In its current version it supports about 70% of the Node.js runtime environment. In particular, it fully supports the Node.js modules, which lets Hop programs reuse existing Node.js modules as is.

A prototype version of Hop.js is currently used by several academic and SME R&D teams to jointly develop an assistive robotic platform and a set of distributed applications.

We plan to release the first public Hop.js version by the end of the first semester of 2015, as we plan to start describing in forthcoming papers.

Multitier Debugging

Debugging Web applications is difficult because of their distributed nature and because the server-side and the client-side of the application are generally treated separately. The multitier approach, which reunifies the two ends of the application inside a unique execution environment, helps the debugging process because it lets the debugger access more runtime informations.

Based on our previous work on the Hop multitier debugger [17] , we have built a multitier debugger for Hop.js, our multitier extension of JavaScript. Its advantage over most debuggers for the Web is that it reports the full stack trace containing all the server-side and client-side frames that have conducted to an error. Errors are reported on their actual position on the source code, wherever they occur on the server or on the client. This paper presents this debugger and sketches its implementation. This work is described in a yet unpublished paper, which will appear in 2015.

Datasource

We extended the hop.js language with an embedded language, inspired by plinq and orc , called datasource . It allows programmers request multiple data sources with queries written in a unique language. We used a plinq-like language to express queries and an orc-like language to orchestrate them. Our query language and the orchastration languages can be used simultaneously or separately. We implemented bindings between datasource and some representative types of data sets such as sparql endpoints, relationnal databases, web services, and web pages. We are extending hop.js by supporting EcmaScript 6 array comprehensions in order to write a unique query over multiple data sources in a unified formalism. The query is then compiled into database specific queries. We linked all the bindings made for hop with hop.js . We implemented another binding for a document oriented data base, mongodb .