November 2018 - curry - lists.rwth-aachen.de

Haskell-related summer internship in Germany
by Finn Teegen 30 Nov '18

30 Nov '18

Our department (PL and compiler construction) again offers a summer internship in 2019 sponsored by DAAD Rise Germany [1]. Undergraduate students enrolled at North American, British and Irish universities are eligible to make an application. We'd be very happy to host a motivated student, who is keen to improve our compiler for the functional logic programming language Curry in terms of performance. For more information you may have a look at our project poster [2]. If you have any questions, feel free to mail any of the contact persons. Please also spread the news to your students and classmates. Cheers, Sandra and Finn [1]: https://www.daad.de/rise/en/rise-germany/ [2]: https://www-ps.informatik.uni-kiel.de/~sad/DAADRise.pdf

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The PAKCS REPL consider something undefined, but the module defining it is loaded
by Jeffrey Brown 29 Nov '18

29 Nov '18

New StackOverflow question! https://stackoverflow.com/questions/53547365/the-pakcs-repl-consider-someth… -- Jeff Brown | Jeffrey Benjamin Brown Website <https://msu.edu/~brown202/> | Facebook <https://www.facebook.com/mejeff.younotjeff> | LinkedIn <https://www.linkedin.com/in/jeffreybenjaminbrown>(spammy, so I often miss messages here) | Github <https://github.com/jeffreybenjaminbrown>

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Specifying default rules: Why and how?
by Jeffrey Brown 23 Nov '18

23 Nov '18

I posted this question on Stackoverflow[1] yesterday and haven't received any answers yet. I've duplicated the question below, but an answer posted to StackOverflow would be more useful to future students, if you're so inclined. Thanks! --- In section 3.5.6 of the Curry tutorial (pdf) <https://www.informatik.uni-kiel.de/~curry/tutorial/tutorial.pdf>, we are advised to use default rules to "regain control after a failed search". The following example is given. (For clarity I have added a type signature and curried the input.) lookup :: k -> [(k,v)] -> Maybe v lookup key (_++[(key,value)]++_ ) = Just value lookup’default _ _ = Nothing I can't get that to compile unless I replace the ’ with a '. Once I do, it behaves like this: test> test.lookup 1 [(2,3)] *** No value found! Question 1: What is the default declaration for? Why would you need to specify that a particular clause is the default one? Won't it be arrived at one way or another, once the others fail? Question 2: How is it written? Should it be written at all? If instead I drop the string 'default: lookup :: k -> [(k,v)] -> Maybe v lookup key (_++[(key,value)]++_ ) = Just value lookup _ _ = Nothing it behaves as intended: test> test.lookup 1 [(2,3)] Nothing test> Has the 'default syntax changed since the tutorial was written? Has it been removed altogether? [1] https://stackoverflow.com/questions/53357361/specifying-default-rules-in-th… -- Jeff Brown | Jeffrey Benjamin Brown Website <https://msu.edu/~brown202/> | Facebook <https://www.facebook.com/mejeff.younotjeff> | LinkedIn <https://www.linkedin.com/in/jeffreybenjaminbrown>(spammy, so I often miss messages here) | Github <https://github.com/jeffreybenjaminbrown>

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What speed to expect doing logic on graphs represented by maps
by Jeffrey Brown 19 Nov '18

19 Nov '18

I want to write something resembling an editor for a graph database. I'm wondering if Curry will be fast enough. The data defining the graph would resemble the following: type Address = Int data Graph = Graph { address :: Map String Address content :: Map Address String -- `address` and `content` are inverses children :: Map Label (Set Address) parents :: Map Label (Set Address) } I would define rules such as: descendent :: Graph -> Index -> Index descendent g i -- If j is i's child, then j is i's descendent. | Set.member j $ Map.lookup i $ children g = j descendent g i -- If j is i's descendent and k is j's child, then k is i's descendent. | descendent g i j & (Set.member k $ Map.lookup k $ children g) = k I'll use hash maps unless their space requirements stop me. I'm hoping the resulting code will quickly (say, in under a second) answer queries over a few million nodes, along the lines of "the descendents of X and Y, minus any descendents of Z or W". If an unbounded number of generations proves computationally difficult, I would not be bothered by needing to impose depth limits, ala "the first two generations of descendents of X and Y, minus the first seven generations of descendents of Z or W". The graph would be sparse: with an average number of children well under five, and few cycles. Is this kind of performance a reasonable thing to expect from Curry? If so, using which compiler? If not, can you recommend another language? I know Haskell, and prefer it immensely to any other language. I am reluctant to write a full application in a pure logic language like Mercury, but I will if need be. -- Jeff Brown | Jeffrey Benjamin Brown Website <https://msu.edu/~brown202/> | Facebook <https://www.facebook.com/mejeff.younotjeff> | LinkedIn <https://www.linkedin.com/in/jeffreybenjaminbrown>(spammy, so I often miss messages here) | Github <https://github.com/jeffreybenjaminbrown>

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