Vivek Haldar

Lurking Smalltalk

Stephen Kell’s paper at PLOS 2013 meditates on one of CS’ oldest design questions: what should be in the operating system, and what in the programming language and runtime? The paper was a breath of fresh air; one of those opinionated design thinking papers that one rarely sees in academic CS venues. Do read the whole thing.

This question comes into stark relief if you look at what a modern language or VM runtime does: among other things, it multiplexes resources, and protect access to them. But that’s also exactly what the OS is supposed to do!

The paper riffs on an earlier idea from Dan Ingalls: “An operating system is a collection of things that don’t fit into a language. There shouldn’t be one.” The central problem tackled in the paper is that of having more generic object bindings in the OS, as opposed to the “static” filesystem bindings for most operations. Kell uses the following example:

Suppose we wish to search some object for text matching a pattern. If the object is a directory tree of text files, grep -r does exactly that. But suppose instead our directory tree contains a mixture of zipped and non-zipped files, or is actually some non-directory collection of text-searchable objects, such as a mailbox. In Smalltalk parlance, how can we make these diverse objects “understand” (via a collection of interposed objects) the messages of our grep -r (and vice versa)?

This would indeed be elegant. But I’m afraid the engineer in me isn’t terribly excited by that.

“All problems in computer science can be solved by another level of indirection” is a famous quote in computer science. The next sentence is much lesser known: “But that usually will create another problem.” What Kell is proposing adds flexibility in binding by introducing indirection.

Indirection is controlled by some sort of configuration the binds each side of it. And configuration implies a lot of added complexity. The UNIX model of “everything is a stream of bytes and can be treated like a file” might be simple and unstructured, but that is precisely what enabled a multitude of structure to be built on top of it.