Higher Logics

I've just added a simple diff algorithm under Sasa.Linq. The signature is as follows: /// <summary> /// Compute the set of differences between two sequences. /// </summary> /// <typeparam name="T">The type of sequence items.</typeparam> /// <param name="original">The original sequence.</param> /// <param name="updated">The updated sequence to compare to.</param> /// <returns> /// The smallest sequence of changes to transform /// <paramref name="original"/> into <paramref name="updated"/>. /// </returns> public static IEnumerable<Change<T>> Difference<T>( this IEnumerable<T> original, IEnumerable<T> updated); /// <summary> /// Compute the set of differences between two sequences. /// </summary> /// <typeparam name="T">The type of sequence items.</typeparam> /// <param name="origina...

There's a great post on implementing idioms with LINQ, and the example application was to implement formlets, as WebSharper does for F#. Tomas's post is well written, so if you're unclear on the above concepts I recommend reading it first before proceeding with this article. The claim in that post is that idioms can only be encoded via LINQ's 'join' operators. While strictly true if you stick to all the LINQ rules, because LINQ queries are just naive syntactic transforms you don't have to follow the rules. You can thus exploit this to hijack the signatures for the SelectMany overloads to yield idiom signatures. It's not all sunshine and roses though, as there are consequences. Overview LINQ is a standard set of methods one can implement that the C# compiler can use to provide "query patterns". This query: var foo = from x in SomeFoo from y in foo.Values select y; is translated by the C# compiler to: var foo = Some...

I had recent need for a transpose operation which could swap the columns and rows of a nested IEnumerable sequence, it's simple enough to express in LINQ but after a quick search, all the solutions posted online are rather ugly. Here's a concise and elegant version expressed using LINQ query syntax: /// <summary> /// Swaps the rows and columns of a nested sequence. /// </summary> /// <typeparam name="T">The type of elements in the sequence.</typeparam> /// <param name="source">The source sequence.</param> /// <returns>A sequence whose rows and columns are swapped.</returns> public static IEnumerable<IEnumerable<T>> Transpose<T>( this IEnumerable<IEnumerable<T>> source) { return from row in source from col in row.Select( (x, i) => new KeyValuePair<int, T>(i, x)) group col.Value by col.Key into c select c as IEnume...

My .NET Sasa library has fallen by the wayside as I experimented with translating various functional idioms in my FP# library. Reading up on what a few other generic class libraries have been experimenting with, like Mono Rocks, spurred me to putting those experiments to use and updating Sasa. I significantly simplified a lot of the code, documented every class and method, and generalized as much as possible. The license is LGPL v2, and you can download the source via svn: svn co https://sasa.svn.sourceforge.net/svnroot/sasa/tags/v0.8 sasa Sasa Core v0.8 A set of useful extensions to core System classes and some useful classes for high assurance development. Named tuple types: Pair, Triple, Quad. Either types, representing one of many possible values. There are Either types for 2, 3, and 4 parameters, mimicking the Pair, Triple, and Quad structure. Tuples are "product" types, while Either is a "sum" type, and products and sums are duals. Since products are useful,...