veyepar: Hop, Skip, Jump: Implementing a concurrent interpreter with Promises

Author(s):	Timothy Jones
Location	Case Room 3
Date	jan Wed 14	Days Raw Files
Start	15:40	First Raw Start	15:06
Duration	0:45:00	Offset	0:33:58
End	16:25	Last Raw End	16:30
Chapters	00:00 0:39:18
Total cuts_time	43 min.

http://lca2015.linux.org.au/schedule/30200/view_talk
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Grace is a relatively new programming language, developed to provide more options for educators introducing programming to students. We have built a non-blocking interpreter for Grace in JavaScript, using a Promise-like API to control asynchronous behaviour. The result is Hopper, an interpreter which can be used as a Node.js command-line tool or as a regular JavaScript library on either Node or the browser. The interpreter uses various techniques to avoid hanging the browser while it is executing, as well as preventing the stack from overflowing during task execution.

This talk will discuss the challenges posed by implementing Hopper. It will investigate the Promises/A+ specification and how our implementation cannot be fully compatible with the spec while providing all of the necessary functionality, and our various attempts at developing our own extensions on top of a compliant system. In particular, we will look at the combination of language features from Grace that require these various extensions, including synchronous APIs, exceptions, and ensuring that 'finally' blocks execute at the appropriate time, as well as demonstrating how easy it is to build concurrent methods for Grace in Hopper. It will also cover the layout of the interpreter and the issue of attempting to support both Node.js and browsers with the same codebase (even in the presence of the browserify tool). Finally, it will consider the challenge of achieving performance in such a setting, where constantly jumping out of execution and deferring to the event loop compounds the more general issue of optimising an interpreter for a dynamic language.

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