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Value-level programmingI was very inspired by the post Scrap your type classes by Gabriel Gonzalez, where he proposes to pass around explicit dictionaries instead of defining instances of type classes. That leads to a distinct style of programming that we may call "value-level programming", where you avoid using any kind of type-directed dispatch and instead pass values around. To show some examples of that style, I wrote a couple blog posts translating generic algorithms from the C++ STL into Java. Where the C++ version uses implicit concepts like "forward iterator" that the types must satisfy, I pass around explicit objects describing these concepts, while keeping the type parameters completely generic. That way you can e.g. use built-in Integers as iterators. The only features used are Java interfaces and basic generics (no type bounds, etc.) In the first post, I do a line by-line translation of the STL algorithm std::partition into Java, in a way that works on both Java's built-in arrays and arbitrary user-defined containers. In the second post, I explore a technique to simulate template specialization from C++, like using a more efficient version of an algorithm when a forward iterator is actually a random access iterator, and demonstrate it with a translation of std::advance. A nice programming language feature to support that style could be something like Agda's instance arguments, to avoid passing around explicit dictionaries all the time. Another related idea can be found in Oleg Kiselyov's delimcc library, where "throwing" and "catching" a specific exception uses a specific value as a point of communication, instead of using the exception's type. It's interesting to translate programming idioms from "type-level" to "value-level" in this way, because it often makes things simpler and more first-class. What do you think? By Vladimir Slepnev at 2014-05-06 16:10 | LtU Forum | previous forum topic | next forum topic | other blogs | 13132 reads
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