Re: [Haskell] Beyond ASCII only editors for Haskell
Mads -- Eons ago, colleagues and I put together a primitive data flow diagram editor and generated functional code for the functions users wired together. One of the things we learned was that people would happily wire together diagrams with state components that could not be translated because they did not represent functions. (Two different data flow paths sharing the same state creates obvious race conditions, but that's what some people wanted to draw.) It was an interesting exercise to build the tool, but I don't think it gave users any great advantage. Perhaps is was a shortcoming of the tool, which was little more than a prototype. However, the informal nature of data flow diagramming at that time seemed to be out of synch with the rigor needed for programming. Good luck with your search -- it may be a good time to try it again. -- Reg Hi One of Haskell's advantages is that it is very suitable as an executable specification language. Which is also claimed on http://www.haskell.org/aboutHaskell.html: "Much of a software product's life is spent in specification, design and maintenance, and not in programming. Functional languages are superb for writing specifications which can actually be executed (and hence tested and debugged). Such a specification then is the first prototype of the final program." also on the same page: "Haskell, a purely functional programming language, offers you: ... * A smaller "semantic gap" between the programmer and the language. " But if I were to specify a program (in a non-executable language) or if I were to write some function on a blackboard, I would not be restricted to only ASCII characters. For example, I would not write 'sqrt 2' but I would write a square root symbol with 2 underneath. Likewise, I would not write '2 ^ 5', but I would write a 2 with a 5 raised upwards to the right of the 2. Then why are we stuck with the mono-spatial ASCII based editors in Haskell? Why is it not possible to make Haskell program look similar to ordinary math? (also when writing those programs and not just afterward in some Latex formatted paper). Also, programmers often use diagrams as specification. As Andrew Bromage says it in http://haskell.org/~shae/pseudocode1.pdf: "Mostly, I strongly suspect that most code of this type is not written, but rather it's translated into. I tend to see many uses of "point-free style" in the same light. It's also one of the reasons why I've resisted using arrows: You don't program in arrow style; you program in diagrams on paper, then translate that into arrow style." This makes me think that our diagrams should be compilable and thus executable? These diagrams could be embedded in our editor and intermixed with ordinary code. I have looked for the type of editor roughly outlined above, but found nothing. If anybody have some links to projects, which is related to these kind of thoughts please let yourself be heard. Also, of cause, comments are most welcome. -- Mads Lindstrøm <[EMAIL PROTECTED]> ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
Re: ICFP programming contest
>Lennart Augustsson wrote: > >>... > >Ooops, I miscounted. It's 376 lines of Haskell; still 137 in the optimizer. >(Not much productivity, just 1 line/minute.) > It appears Lennart is exercising his well-deserved bragging rights. :^) More power to him. Congratulations Lennart, and to all the other contestants as well! (I chickened out. Wisely, I think.) Thanks also to those who set up the contest. I would be interested in hearing from other contestants about how they think their programming language helped (or didn't help) them solve the problem. What language features were most helpful? Did anything particular get in the way? How much code did solutions take in other languages? Any smaller than 376 lines? Any teams more productive than 1 line/minute? -- Reg
Re: Monad question
This little problem raises two challenges for compiler developers: (a) improving diagnostic messages (a perennial issue), and (b) (semi) automating error correction. In this case the diagnostic message is pretty good, except that is doesn't indicate where the IO term is or where the [] term is that doesn't match. This is the critical piece of information Malcolm added to explain the problem. It seems that lifting would be a natural extension to the type unification process to allow automating "corrections". When you find several possible lifting functions, of course, you are in trouble. But then you could add that information to the diagnostic message. This may be trying too hard to help the fat fingered programmer (aka, yours truly) who simply entered an incorrect expression. Reactions anybody? Thanks to Malcolm and the other responders for such clear explanations and clean solutions. -- Reg >> getDirectoryContents "." >>= filter (\(x:_) -> x /= '.'); >> [65] Cannot unify types: >> Prelude.IO >> and (Prelude.[]) > >The problem is that `filter's result type is [a], not >(IO [a]) which its use as an argument to >>= requires. >The fix is easy: lift its result into the monad (using `return'). > > getDirectoryContents "." >>= return . filter (\(x:_) -> x /= '.') >
Re: Function denotations
Reply to: RE>Function denotations I'm sure many people would find printable function representations useful. There are at least three versions of every function I've ever written: the function I meant (fm), the function I wrote (fw), and the function the compiler/interpreter produced/executed (fx). When tests show that fx /= fm, some visibility into fx can be most helpful. Even if the correspondence between fw and fx is a stretch, knowing more about fx often points to the problem with fw. This issue isn't really one of language definition, though. It seems to me it's an issue for programming support environments. I don't know of any language standard that includes requirements for debugging tools. Any implementers willing to give this a whirl?
Re: Arrays and general functions
Interesting discussion, but it seems to me that Haskell already provides the best of both worlds, namely a. Efficient implementation of arrays as data objects, with indexing as a projection function; and b. Definition of functions with (Ix a) domains by indexing an array behind the scenes or by any other rule. Arrays satisfy the needs of an important user community. Is there something more needed to satisfy the general-function community?
