On May 28, 2007, at 7:32 AM, Claus Reinke wrote:
I meant to imply more that "it's very difficult to understand why it's useful". If an extension were truely *useless*, I doubt those guys at GHC would have bothered spending years implementing them.Most of the documents that describe these things begin with "suppose we have this extremely complicated and difficult to understand situation... now, we want to do X, but the type system won't let us." Which makes it seem like these extensions are only useful in extremely complicated and rare situations.keep in mind that paper space is a precious and limited resource. theneed for extensions tends to arise in practice first, but those real examples are far too big and complex to fit into those limitations. it is very difficult to come up with examples that are small enough to fit, yet complex enough to exhibit the problem. which means that the examples usually look artificial, but small and complete, or realistic, but so large that their presentationhas to be shallow enough to border on vague.
But I do wonder if we shouldn't declare a moratorium on examples that involve interpreters for simply-typed languages (which tend to characterize none of the problems I'm actually trying to solve---and that includes fiddling with non-simply-typed languages of a similar sort) in favor of examples which actually perform some sort of a useful manipulation.
This is why I absolutely LOVE functional pearls of all sorts, by the way.
-Jan-Willem Maessen
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