[Haskell-cafe] FGL problem: cannot acces data constructor NodeMap
Hi, I have a problem with the data constructor NodeMap Data.Graph.Inductive.NodeMap of the graph library fgl-5.4.2.3 (also fgl-5.4.2.2): I cannot access the data constructor NodeMap, as the ghci session shows: Prelude :m Data.Graph.Inductive.NodeMap Prelude Data.Graph.Inductive.NodeMap :t NodeMap interactive:1:0: Not in scope: data constructor `NodeMap' However, when I load the source directly it works: Prelude :l Data/Graph/Inductive/NodeMap.hs [1 of 3] Compiling Data.Graph.Inductive.Graph ( Data/Graph/Inductive/Graph.hs, interpreted ) [2 of 3] Compiling Data.Graph.Inductive.Internal.FiniteMap ( Data/Graph/Inductive/Internal/FiniteMap.hs, interpreted ) [3 of 3] Compiling Data.Graph.Inductive.NodeMap ( Data/Graph/Inductive/NodeMap.hs, interpreted ) Ok, modules loaded: Data.Graph.Inductive.Internal.FiniteMap, Data.Graph.Inductive.Graph, Data.Graph.Inductive.NodeMap. *Data.Graph.Inductive.NodeMap :t NodeMap NodeMap :: (Ord a) = FiniteMap a Node - Int - NodeMap a Why is that so? Afterall, my purpose is to get access to the map in a NodeMap and finally to apply lookup to it. But I don't know how to access the map from a NodeMap (the map selector isn't accessible either). Immanuel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] FGL problem: cannot acces data constructor NodeMap
Immanuel Normann immanuel.norm...@googlemail.com writes: Hi, I have a problem with the data constructor NodeMap Data.Graph.Inductive.NodeMap of the graph library fgl-5.4.2.3 (also fgl-5.4.2.2): I cannot access the data constructor NodeMap, as the ghci session shows: Prelude :m Data.Graph.Inductive.NodeMap Prelude Data.Graph.Inductive.NodeMap :t NodeMap interactive:1:0: Not in scope: data constructor `NodeMap' Well, yes, because you're not meant to. However, when I load the source directly it works: Prelude :l Data/Graph/Inductive/NodeMap.hs [1 of 3] Compiling Data.Graph.Inductive.Graph ( Data/Graph/Inductive/Graph.hs, interpreted ) [2 of 3] Compiling Data.Graph.Inductive.Internal.FiniteMap ( Data/Graph/Inductive/Internal/FiniteMap.hs, interpreted ) [3 of 3] Compiling Data.Graph.Inductive.NodeMap ( Data/Graph/Inductive/NodeMap.hs, interpreted ) Ok, modules loaded: Data.Graph.Inductive.Internal.FiniteMap, Data.Graph.Inductive.Graph, Data.Graph.Inductive.NodeMap. *Data.Graph.Inductive.NodeMap :t NodeMap NodeMap :: (Ord a) = FiniteMap a Node - Int - NodeMap a Why is that so? This works because you're using ghci from within the module, whereas when you import it you're using only its exposed API. Afterall, my purpose is to get access to the map in a NodeMap and finally to apply lookup to it. But I don't know how to access the map from a NodeMap (the map selector isn't accessible either). You're not meant to; the point of NodeMap is to serve as a wrapper around the normal graph types, not for you to use directly (exactly the same as why the constructor for Map isn't exported). May I ask, however, why you want to use Data.Graph.Inductive.NodeMap? -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] FGL problem: cannot acces data constructor NodeMap
CC-ing haskell-cafe again: Immanuel Normann immanuel.norm...@googlemail.com writes: 2010/7/24 Ivan Lazar Miljenovic ivan.miljeno...@gmail.com Immanuel Normann immanuel.norm...@googlemail.com writes: Afterall, my purpose is to get access to the map in a NodeMap and finally to apply lookup to it. But I don't know how to access the map from a NodeMap (the map selector isn't accessible either). You're not meant to; the point of NodeMap is to serve as a wrapper around the normal graph types, not for you to use directly (exactly the same as why the constructor for Map isn't exported). May I ask, however, why you want to use Data.Graph.Inductive.NodeMap? Some of my lnodes in the graph have by construction unique labels and I want to lookup the lnode from a graph given only the label of that lnode. Well, from my understanding NodeMap doesn't do what you want, since it assumes that _all_ of the node labels are unique. Furthemore, the way of using it seems to be analogous of how one would use a State monad rather than for actual interactive use throughout. -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] FGL problem: cannot acces data constructor NodeMap
Once again cc-ing -cafe; Immanuel, can you please do reply to all
rather than just reply in GMail? :p
Immanuel Normann immanuel.norm...@googlemail.com writes:
2010/7/24 Ivan Lazar Miljenovic ivan.miljeno...@gmail.com
CC-ing haskell-cafe again:
Immanuel Normann immanuel.norm...@googlemail.com writes:
2010/7/24 Ivan Lazar Miljenovic ivan.miljeno...@gmail.com
Some of my lnodes in the graph have by construction unique labels and I
want
to lookup the lnode from a graph given only the label of that lnode.
Well, from my understanding NodeMap doesn't do what you want, since it
assumes that _all_ of the node labels are unique
I wouldn't bother when NodeMap maps also non-unique labels to single nodes,
because I only lookup nodes with unique labels, e.g. assume my label are of
the form
data Label = Unique String | Multi Label
I'm of the suspicion that using NodeMaps in this fashion will have
problem when considering nodes with the same label (even if you don't
explicitly use it for those nodes), as NodeMap seems to assume that node
labels are unique.
For example, mkNode assumes node labels are unique.
Furthemore, the way of using it seems to be analogous of how one would use a
State monad
rather than for actual interactive use throughout.
Could you elaborate this further, please.
http://hackage.haskell.org/packages/archive/fgl/5.4.2.3/doc/html/Data-Graph-Inductive-NodeMap.html#v%3Arun
and
http://hackage.haskell.org/packages/archive/fgl/5.4.2.3/doc/html/Data-Graph-Inductive-NodeMap.html#v%3Arun_
If you just want a mapping from labels to nodes, you may be better off
using your own custom Map (and maybe even defining a new graph type that
has such a Map as part of it).
The successor to FGL-5.x (whatever we'll end up calling it) will allow
you to have custom node types rather than using Ints. However, this
will not work for you in this situation.
The node type is just an _index_ type, analogous to the actual hash
value in a hash{map,array} (as opposed to the value which has the
hashing function applied upon it). It's there to provide a unique
identifier for a particular node. Arguably, an abstract type would be
even better as an Int as it will prevent you from doing silly things
like adding node indices together, but that's beside the point.
If you wish to find a node with a specific label, try using something
like gsel:
http://hackage.haskell.org/packages/archive/fgl/5.4.2.3/doc/html/Data-Graph-Inductive-Basic.html#v%3Agsel
--
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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Re: [Haskell-cafe] FGL problem: cannot acces data constructor NodeMap
2010/7/24 Ivan Lazar Miljenovic ivan.miljeno...@gmail.com
Once again cc-ing -cafe; Immanuel, can you please do reply to all
rather than just reply in GMail? :p
Oh, yes I forgot - sorry!
Thanks for all the valuable infos :-)
Immanuel
Immanuel Normann immanuel.norm...@googlemail.com writes:
2010/7/24 Ivan Lazar Miljenovic ivan.miljeno...@gmail.com
CC-ing haskell-cafe again:
Immanuel Normann immanuel.norm...@googlemail.com writes:
2010/7/24 Ivan Lazar Miljenovic ivan.miljeno...@gmail.com
Some of my lnodes in the graph have by construction unique labels and
I
want
to lookup the lnode from a graph given only the label of that lnode.
Well, from my understanding NodeMap doesn't do what you want, since it
assumes that _all_ of the node labels are unique
I wouldn't bother when NodeMap maps also non-unique labels to single
nodes,
because I only lookup nodes with unique labels, e.g. assume my label are
of
the form
data Label = Unique String | Multi Label
I'm of the suspicion that using NodeMaps in this fashion will have
problem when considering nodes with the same label (even if you don't
explicitly use it for those nodes), as NodeMap seems to assume that node
labels are unique.
For example, mkNode assumes node labels are unique.
Furthemore, the way of using it seems to be analogous of how one would
use a
State monad
rather than for actual interactive use throughout.
Could you elaborate this further, please.
http://hackage.haskell.org/packages/archive/fgl/5.4.2.3/doc/html/Data-Graph-Inductive-NodeMap.html#v%3Arun
and
http://hackage.haskell.org/packages/archive/fgl/5.4.2.3/doc/html/Data-Graph-Inductive-NodeMap.html#v%3Arun_
If you just want a mapping from labels to nodes, you may be better off
using your own custom Map (and maybe even defining a new graph type that
has such a Map as part of it).
The successor to FGL-5.x (whatever we'll end up calling it) will allow
you to have custom node types rather than using Ints. However, this
will not work for you in this situation.
The node type is just an _index_ type, analogous to the actual hash
value in a hash{map,array} (as opposed to the value which has the
hashing function applied upon it). It's there to provide a unique
identifier for a particular node. Arguably, an abstract type would be
even better as an Int as it will prevent you from doing silly things
like adding node indices together, but that's beside the point.
If you wish to find a node with a specific label, try using something
like gsel:
http://hackage.haskell.org/packages/archive/fgl/5.4.2.3/doc/html/Data-Graph-Inductive-Basic.html#v%3Agsel
--
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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