Re: [Haskell-beginners] Noobie attempt to process log output into dependency graph

Thanks, all, that gives me something to chew on. It occurred to me (during my 45-minute commute to work) that all Haskell programs (listen to the noob <eyeroll/>) have the following structure (modulo my fractured syntax): main :: IO() main = do inputs <- getInputs doOutput $ f inputs initialState f :: [input] -> state -> outputs f [] state = transformToOutputs state f (input:inputs) state = f inputs (newState state input) doOutput :: [output] -> IO() doOutput outputs = do putStr $ unlines outputs So all I have to do is write newState and I'm good! ^_^ (transformToOutputs will, of course, be a snap.) Right? John. On Thu, Dec 15, 2016 at 2:38 PM, Magnus Therning wrote:

John Lusk writes:

...

I have not, but I might. This was a little work project that I've now run out of time for.

I was really hoping for a deeper discussion of state management than "just use this package." This seems kind of like receiving a stream of inputs from a user and needing to keep track of several items of state that are changing independently (as opposed to the neat problems usually used in basic FP education).

Should I be taking a more monadic approach?

Well, we have to start somewhere :)

Anyway, you don't necessarily have to resort to the state monad. I believe, based you your other code that you quite easily can go from your list of lines to a list of `(Int, String)`, where the integer indicates the indentation level. Then you can look at `Data.Tree` (in containers) and `Data.Tree.Zipper` (in rosezipper) to build your tree.

This is my quick hack:

~~~ buildTree _ zipPos [] = zipPos buildTree n zipPos xx@((lvl, s):xs) | lvl > n = let newZipPos = children zipPos node = Node s [] in buildTree lvl (insert node newZipPos) xs | lvl == n = let newZipPos = nextSpace zipPos node = Node s [] in buildTree lvl (insert node newZipPos) xs | lvl < n = let (Just newZipPos) = parent zipPos in buildTree (n - 1) newZipPos xx ~~~

With the following definitions in place:

~~~ ils = [ (1, "The root") , (2, "Child 1") , (3, "Child 1.1") , (4, "Child 1.1.1") , (3, "Child 1.2") , (2, "Child 2") ]

zipRoot = fromTree $ Node "absolute top" [] ~~~

I build the tree, and print it, like this:

~~~ putStrLn $ drawTree $ toTree $ buildTree 0 zipRoot ils top | `- The root | +- Child 1 | | | +- Child 1.1 | | | | | `- Child 1.1.1 | | | `- Child 1.2 | `- Child 2 ~~~

Whether this is usable for you depends a lot on how big your logs are, I suppose.

If this was something that I'd keep around for a while I'd probably look into rewriting `buildTree` so that it would fit for use with `mapAccumL`.

/M

-- Magnus Therning OpenPGP: 0x927912051716CE39 email: magnus@therning.org jabber: magnus@therning.org twitter: magthe http://therning.org/magnus

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