I am lost. The essential idea of coherence is a year old, and I still haven’t implemented it. I blame the trees. I have been struggling to integrate coherence with the tree-based model of computation in Subtext. It just isn’t working. In fact it hasn’t been working for years – I have struggled with the subtleties of trees in my last 4 papers. And the reviewers seemed to have struggled as well. My conclusion is that these trees are standing in the way of progress, and they have to come down.<\/p>\n
I have been hugging trees because they seemed essential to my long-term agenda. But I realize now that if I defer the more ambitious aspects, I can still achieve some major goals with a more normal language, one that uses syntax for code and objects for data. Such a language is not only a lot simpler to invent, but also a lot more approachable to everyone else. Three realizations make this simplification now seem viable.<\/p>\n
Firstly, I have remembered that I can make a syntactic language still appear to be live and example-centric in the IDE. That is what I did back in my original Example Centric Programming<\/a> paper. That work was limited to a purely functional subset of Java. But now with coherence I can equally well visualize the execution of imperative code in the IDE.<\/p>\n Secondly, I can construct updatable views out of objects. My last paper talked about virtual trees, which are computed on demand, but can be read and written like normal trees. I can do the same thing with objects by automatically generating getter and setter methods, and by carefully limiting their visibility. Collections have to change substantially. This will not be a plain vanilla object model.<\/p>\n Thirdly, I can do hypothetical imperative computations (progressions in the paper) using object spaces<\/em>. A space appears to be a copy of the entire heap, except with some specific changes. Spaces nest, which may offer some of the hierarchical goodness of trees, like deep copying.<\/p>\n The road forward looks like this: right now I am working on my talk at OOPSLA this month. I only have a 20 minute slot, so it will not be very deep. As usual I’ll post a video after the talk. Concurrently, I am working on an informal description of the syntax and semantics of the language to cover roughly the same capabilities as in the paper. I will try to present that in more detail later this fall at NEPLS. Then I need to do a prototype implementation, probably as a REPL without an IDE. <\/p>\n