I'm reading some documentation on IxSet's http://happstack.com/docs/crashcourse/AcidState.html#ixset , and I was wondering about looking at source of Indexable typeclass which is imported from Data.IxSet.
So then I took a repository of Happstack and looked there (darcs get http://patch-tag.com/r/mae/happstack), but that got me to even bigger frustration.
I see the happstack/happstack-ixset/src/Happstack/Data/IxSet.hs file, which creates a module Happstack.Data.IxSet, but I can't see which file creates a module Data.IxSet (and implements class Indexable).
The go-to address for Haskell code is hackage. There is conveniently a link to Hayoo on the front page, the other major Haskell search engine besides Hoogle. Both have advantages above the other.
Hayoo indexes all packages on hackage and the searches by default include all packages on hackage. If you want to search for a known name, e.g. Indexable, that is the more convenient engine, especially if you don't know which package the name comes from. The - currently - fifth hit takes you to Data.IxSet.Indexable. On the right hand side of the Haddock docs, you find a Source link that takes you to the hscoloured sources (in this case, that's not very informative, though, there's only one class member, without default implementation, it tells you nothing above the docs).
Hoogle searches only a small number of packages by default, if you want to include other packages in the search, you have to specify that by adding +packagename to the search - but that restricts the search to the specified package. More about Hoogle searches in the manual. Hoogle's strength is the search by type. Hoogle's search by type applies more transformations to the searched type, and thus finds more matches than Hayoo's if you don't know the exact type (that is not without downsides, however, sometimes you get a lot of irrelevant hits). If you search for example Map k a -> k -> Maybe a, Hoogle's first result is the most likely candidate Data.Map.lookup :: Ord k => k -> Map k a -> Maybe a, whereas Hayoo doesn't find that because it doesn't permute arguments.
Either way, both search engines lead you to hackage's Haddock docs for the queried entity (if the search was successful), from where the Source links take you to the code, if you wish.
Use Haddock documentation, locally-generated or online. Google search usually returns relevant docs near the top. The documentation is cross-linked so you can surf to the module you need. There's a link to the source next to each definition, for example.
This particular module belongs to the base libraries set.
Related
today on "adventures in functional programming with lenses" our hero attempts to define a prism over a list element that may or may not exist.
It's a bit tricky to explain, so to avoid the X, Y problem I'll give the actual use-case in all its glory.
I'm writing a Text editor in Haskell called Rasa, the whole idea is that it's extremely extensible, and that means most functionality is written as extensions. Since it's a core principle, extensions ALSO depend on other extensions, so I needed a way to store their state centrally such that all extensions depending on an extension could access its current 'extension state'. Of course the types of these states is not known to the core of the editor, so at the moment I'm storing a list of Dynamic values. When the extension stores the state it converts to a Dynamic, then it can be extracted later via a prism like so:
data Store = Store
{ _event :: [Event]
, _editor :: E.Editor
, _extState :: [Dynamic]
}
ext :: Typeable a => Traversal' Store a
ext = extState.traverse._Dynamic
So now ext is a polymorphic Traversal that essentially operates over only the Dynamics that 'match' the type in question (if you set to it it'll replace values of the same type, if you 'get' from it, it acts as a traversal over the Dynamics that match the type of the outbound value). If that seems like magic, it basically is...
BTW, I'd love to have exactly 1 copy of a given Extension's state object in the list at any time.
So getting and setting is actually working fine IFF there's already a value of the proper type in the list, my question is how can I make a version of this Traversal such that if a value of the proper type is in the list that it will replace it (and getting works as expected), but that will ADD a value to the list if the traversal is SET to and there's NO matching element in the list. I understand that Traversal's aren't supposed to change the number of elements that they're traversing, so perhaps this needs to be a prism or lens over the list itself?
I understand this is really confusing, so please ask clarifying questions :)
As for things I've taken a look at already, I was looking at prefixed and _Cons as possible ways to do this, but I'm just not quite sure how to wire it up. Maybe I'm barking up the wrong tree entirely.
I could perhaps add a default value to the end of the traversal somehow, but I don't want to require Monoid or Default so I can't conjure up elements from nowhere (and I only want to do it when SETTING).
I'm also open to discussions about whether this is actually the proper way to store this state at all, but it's the most elegant of solutions I've found so far (though I know typecasting at run time is sub-optimal). I've looked into the Vault type, but passing keys around didn't really work well when I tried it (and I imagine it has similar type-casting performance issues).
Cheers! Thanks for reading.
I think the list of extensions is not proper solution for you. I would be added something like _extState :: Map TypeRep Ext where data Ext = forall a. Ext a. Then I would be added the lens:
ext :: forall a . Typeable a => Lens' Store (Maybe a)
ext = _extState . at (typeRep (Proxy :: Proxy a)) . mapping coerce
where
coerce = iso (\(Ext x) -> unsafeCoerce x) Ext
This lens does like at. So you can simply get/set your extensions.
But there is one limitation, all extensions must be of different types.
I would like to change the behavior of menhir's output in follwoing way:
I want it to look up all grammatical alternatives if it finds any, and put them in a list and get me back this ambigouus interpretation. It shall not reduce conflicts, just store them.
In the source code of menhir, it seems to me, that I have to look in "Engine.ml". The resultant syntactically determined token comes in a variant type item "Accepted v" as a state of a checkpoint of the grammatical automaton. This content is found by a function "accept env prod" before, that is part of a bundle of recursive functions, that change the states.
Do you have a tip, how I could change these functions to put all the possible results in the list here and proceed as if nothing happened? Or do you think, that this wont work anyway?
Thanks.
What you are looking for is a GLR parser generator (G is for generalized). Menhir is not such tool, and I doubt you could modify it easily to do what you want.
However, there is another tool that does exactly what you want: dypgen.
I'd like to use latex notation for equations in my source code.
For example, I would write the following comment in some haskell source file Equations.hs:
-- | $v = \frac{dx}{dt}$
In the doc directory, this gets rendered by haddock in Equations.tex as:
{\char '44}v = frac{\char '173}dx{\char '175}{\char '173}dt{\char '175}{\char '44}
I found this function in the source for Haddock's latex backend that replaces many characters that are used in latex formatting:
latexMunge :: Char -> String -> String
...
latexMunge '$' s = "{\\char '44}" ++ s
Is there any existing functionality that allows me to bypass this and insert latex equations in comments?
No. The main reason why this (and similar features) don't exist is that it's unclear what to do with the markup in the other backends, be it HTML one, Hoogle one or whatever else someone might be using. This is fairly commonly requested but there is no common agreement and more importantly, no patches.
Technically we don't support the LaTeX backend, it's kept around compiling so that the Haskell Report can be produced. If you or someone else wants to give it some new life (and features) then we'll happily accept patches.
tl;dr: no can do. I know people simply pre-render LaTeX and insert the resulting images in with the image syntax.
I need to create a function f:: Log->[String] that does that (((o, i ,d),s) = [(o, i ,d)]
type Log = (Plate, [String])
type Plate = (Pin, Pin, Pin)
type Pin = (Char, Int)
If you're on a page like this, click "Source" on the fir right side, next to the function that you're interested in.
If you need to look up a function, Hayoo! and Hoogle will link you to documentation pages like the one above.
An important thing to note, though is that show doesn't have one definition. show is a function defined for all data types in the Show (with a capital "S") typeclass. So for example, here is the full source for the Show typeclass. Show is defined within the typeclass as just show :: a -> String. But if you search for "instance Show Bool" or "instance Show Int", you'll find specific definitions.
For the second part of your question, the easiest way to get a show function for a new type is to simply write deriving (Show) below it. For example,
data Foo = Foo Int Int
deriving (Show)
Now I can use show on data with type Foo.
g :: Log -> [String]
g (plate, _) = [show plate]
Use hoogle to find this sort of information.
Example: http://www.haskell.org/hoogle/?hoogle=show
Once you've found the function you'd like in the list, click and there you'll find a Source link on the right hand side of the page.
NB this is an answer to the original question:
Where can I see the codes of the predefined functions in haskell ?? Mainly the function SHOW?
It's true that you can use Hoogle to search for functions defined in the Prelude (and other modules), but the source code itself is located at Hackage.
Hackage is a database of Haskell packages. You can download new packages from it, and also view the Haddock documentation for every package in the database.
This is the Haddock page for the standard Prelude. It documents the type classes, data types, types, and top-level functions exported by the Prelude module. To the right of each definition header is a link that says "Source". You can click this to be taken to an online copy of the source code for the module you're viewing.
On preview, you're now asking a different question entirely, and on preview again in fact the original question has been edited out of this post.
Your new question is unclear, but this solution will work to produce the output in your example.
> [fst ((('O',0),('I',0),('D',1)),"O->D")]
[(('O',0),('I',0),('D',1))]
I think you're using list notation instead of double quotes to identify Strings, by the way, so I fixed that around 0->D above. So you might also try this instead.
> show (fst ((('O',0),('I',0),('D',1)),"O->D"))
"(('O',0),('I',0),('D',1))"
This works because you have only defined type synonyms (by using type in your declarations instead of data) on data structures which already have Show instances.
I always have difficulty in finding all available alternative ways to produce a specific graph, either one that I have already decided to use (looking for different variations) or one that I have not yet thought of.
The R Graphical Manual site provides a complete list of samples of R's graphics functions, however it's easier for me to search providing a package name (how else -for example- can I get a resultset including superbarplot function, when I want to look for barplots?. Let alone that the superbarplot graph does not appear in the results even if I try searching for it's package: UsingR)
The R-SAS-SPSS Add-on Module Comparison - and especially on topic Graphics, Static in the table provided - gave me the idea that it would be nice to have a place where all relevant packages are listed by topic.
Do you have any idea about something like that?
If you're interested in learning about all the possible graphics you can make, you should learn about the grammar of graphics, and (my) implementation of it in R: ggplot2.
Your question, or the general pattern anyway, was clearly a primary use case for the design of the sos package.
sos actually goes one step further that your question requires by identifying particular functions with packages; in addition, it ranks the results by relevance (by default, you can change the default behavior via the "sortby" parameter, e.g., sortby="Date")
Here's how it works:
most of this package's functionality is exposed via the "findFn" command
for instance, if you want a list of all functions and the parent package related to scatter plots:
findFn("scatter plot", maxPages=2, sortby="TotalScore")
This returns a dataframe formatted as HTML table and delivered in your default browser (if you don't want it to pop-up immediately, then just bind the function call to a variable and then call the variable when you're ready)
The right-most column of the dataframe/HTML page is "Description and Link". Clicking an entry in that column opens another tab in your browser (according to the user-set preferences set in your browser) with the complete R help page for that function.
The results from the function call above show, for instance, that the functions for plotting data in a 'scatter plot' format are found in the following packages:
ade4 (function: scatter)
IDPmisc (functions: ipairs, iplots)
GGally (function: ggally_points)
PerformanceAnalytics (function:
chart.Scatter)
mclust (function: clPairs)
Another example:
findFn("boxplot", maxPages=2, sortby="TotalScore")
identifies these (among others) packages/functions for plotting boxplots:
sfsmisc (function: boxplot.matrix)
aplpack (function: boxplot2D)
NADA (function: boxplot-methods)
StatDA (function: rg.boxplot)
plotrix (function: gap.boxplot)
gplots (function: boxplot.n)
multcompView (function:
multcompBoxplot)
oligo (function: boxplot)
Have you seen the R Graph Gallery ?
Other than that, you may have to index all the source code of CRAN packages to search efficiently...
these are good memory-joggers. I second the ggplot2 recommend, also recommend looking thru CRAN views:
http://cran.r-project.org/web/views/
http://cran.fhcrc.org/web/views/Graphics.html
(this mirror seems faster in west coast US)
http://dataspora.com/archive/2009/seminar/Survey_of_R_Graphics_by_Driscoll_Dataspora_Jun2009.pdf
http://zoonek2.free.fr/UNIX/48_R/04.html
(possibly world's longest webpage)
http://www.stat.auckland.ac.nz/~ihaka/120/lectures.html
Ihaka's lectures notes