I think that the difficulties you are facing are from the fact that you are trying to express a purely functional "updatable" graph.
Should I understand from this, that this is a difficult problem and that there exist no easy way to do this at the moment?
Well, I think he was being a bit ironic. You can either have a functional graph or an updatable graph, but not both. It sounds like either would do and given that later in this message you discuss that you don't like imperativeness, then a functional graph (ala the Functional Graph Library -- FGL) would suit you perfectly.
About the graphs:Well, I never had graphs at school yet(first year student)... Although it is somewhere in my textbooks...
They're very simple. You have a collection of nodes, N, and a collection of edges between elements of N. Nodes and edges can have labels. So for instance you could have Teachers and Classes as the nodes and the edges could be between the teacher and the class(es) which go together.
To solve my problem... I need an mutable array, but in Haskell my program will then be unbelievable imperative.
No, you just need a graph :).
I have been following the discussion about the graph and so, but the arrow classes and so on, are like something too sophisticated for me at this moment I think, although I have some idea of how they work, I really don't know when to apply them. I just found out, how Monads work, so...
THe discussion about arrows is a complete divergence. You don't need anything about them.
But I certainly believe that my problem must be fixed before it's easy to program in Haskell.
Theorem: this problem is already fixed. Proof: it is easy to program in Haskell. QED. :) - Hal
--- Hal Daume
I think that the difficulties you are facing are from the fact that you are trying to express a purely functional "updatable" graph.
Should I understand from this, that this is a difficult problem and that there exist no easy way to do this at the moment?
Well, I think he was being a bit ironic. You can either have a functional graph or an updatable graph, but not both. It sounds like either would do and given that later in this message you discuss that you don't like imperativeness, then a functional graph (ala the Functional Graph Library -- FGL) would suit you perfectly.
About the graphs:Well, I never had graphs at school yet(first year student)... Although it is somewhere in my textbooks...
They're very simple. You have a collection of nodes, N, and a collection of edges between elements of N. Nodes and edges can have labels. So for instance you could have Teachers and Classes as the nodes and the edges could be between the teacher and the class(es) which go together.
To solve my problem... I need an mutable array, but in Haskell my program will then be unbelievable imperative.
No, you just need a graph :).
I have been following the discussion about the graph and so, but the arrow classes and so on, are like something too sophisticated for me at this moment I think, although I have some idea of how they work, I really don't know when to apply them. I just found out, how Monads work, so...
THe discussion about arrows is a complete divergence. You don't need anything about them.
But I certainly believe that my problem must be fixed before it's easy to program in Haskell.
Theorem: this problem is already fixed. Proof: it is easy to program in Haskell. QED.
:)
- Hal
I have read the chapter in my textbook :) and I have read and played with the FGL module. I must say the FGL module looks impressive, but I find it hard to start with it, because the most intuitive way of doing it for me was, to have different datatypes for Teacher Subject and so on. But it looks the Graph class works on types a and b where a is the Node type where b is the Edge type, or just the other way around :), I don't have the code right now. The above rules out my way of representing the data, or doesn't it (i.e. is there some fancy, magical way of doing this) ? The second intuitive solution is to take a datatype like data GraphNode|Teacher etc |Subject etc |Student etc Should this be the way to do it? And then yet another question: I need some kind of way to remember, which possibilities I already had. In example in my C++ program I used a couple of array's with in each array pointers to the StudentObjects, TeacherObjects. So I had the notion of the first teacher, the second teacher, the third and so on(in 0(1)), although I only need the notion of did I test this possibility and give me the next of Student/Teacher/whatever. I must be able to put it somewhere, but where? In the Graph itself there isn't really space for it, unless I create a complete timetable in the beginning with all Studentnodes pointing to this first teacher. But now I have to be able to change the Graph in such a way that I can change the first node where an error(schedulingerror) occurs, (for example a "room is full" error) to let the Student point to the next room(see the notion above). But then I yet have another problem. How can I guarantee, to do a complete path traversal, each time in exactly the same way? Greets Ron __________________________________ Do you Yahoo!? SBC Yahoo! DSL - Now only $29.95 per month! http://sbc.yahoo.com
participants (2)
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Hal Daume -
Ron de Bruijn