Accessing loosely structured data from F# and C# (GOTO 2011)

About two weeks ago, I gave a talk at GOTO Conference in Copenhagen at a very interesting .NET session organized by Mark Seemann. In my talk, I focused on the impedance mismatch between the data structures that are used in programming languages (such as classes in C# or records and discriminated unions in F#) and the data structures that we need to access (such as database, XML files and REST services).

Clearly, both of the sides have some structure (otherwise, it wouldn't be possible to write any code against them!). Even an XML file that is returned by a REST service has some structure - although the only way to find out about the structure may be to call the service and then look at the result. In this article, I'll briefly summarize the ideas that I presented in the talk. Here are links to the slides as well as the source code from the talk:

• You can browse the slides at SlideShare or you can download them from GitHub in the PPT format.
• The source code is in my GitHub repository and can be downloaded as a single ZIP file.

Explicit speculative parallelism for Haskell's Par monad

Haskell provides quite a few ways for writing parallel programs, but none of them is fully automatic. The programmer has to use some annotations or library to run computations in parallel explicitly. The most recent paper (and library) for writing parallel programs follows the latter approach. You can find more information about the library in a paper by Simon Marlow et al. A monad for deterministic parallelism and it is also available on Hackage. However, I'll explain all the important bits that I'll use in this article.

The library provides an explicit way for writing parallel programs using a Par monad. The library contains constructs for spawning computations and sharing state using blocking variables. However, the whole programming model is fully deterministic. I believe that it is sometimes useful to lift the determinacy requirement. Some programs are deterministic, but the fact cannot be (easily) automatically verified. For example, say you have two functions fib1 and fib2. They both give the same result, but each of them is more efficient than the other one on certain inputs. To calculate a Fibonacci number, the program could speculatively try to evaluate both functions in parallel and return the result of the one that finishes first.

Unfortunately, this cannot be safely implemented using a fully deterministic library. In this article, I'll show some examples where speculative parallelism can be useful and I'll talk about an extension to the Par monad that I implemented (available on GitHub). The extension allows programmers to write speculative computations, provided that they manually verify that their code is deterministic.

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