- Glasgow-haskell-users

example for recursive import
by Serge D. Mechveliani 07 Jun '06

07 Jun '06

Johannes Waldmann <waldmann(a)imn.htwk-leipzig.de> writes on Junne 6 2006 > As for recursive module imports, > could you perhaps show an example where this occurs. > I found that in my code, I can re-arrange things > so as to remove the cyclic dependency. Best regards, Consider the following situation, which often happens. * A function f calls for g and for h, each g and h calls for f. * f is a large implementation, gathered in the module F. * g and h are the two important special cases for f, each implemented as a large source, according to its very particular principles. * Each of these three functions needs only a small part of the name space needed for other two functions (modules are also for structuring the name space). >From the conceptual point of view, we need at least three modules in this case. This way this program is easier to write and to understand. But the module import occurs cyclic. ----------------- Serge Mechveliani mechvel(a)botik.ru

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why hs-boot
by Serge D. Mechveliani 07 Jun '06

07 Jun '06

For recurive import, GHC suggests using an hs-boot file to "get started". So far, I do not know, what does this mean. But I do not understand, why at all GHC needs any help in this situation. Look: * we write the two modules importing each other, * reading these modules, we understand the computational meaning of the whole program. Hence, it must be compiled according to this meaning. Why does GHC need additional help? Thank you in advance for explanation. ----------------- Serge Mechveliani mechvel(a)botik.ru

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recursive import
by Serge D. Mechveliani 06 Jun '06

06 Jun '06

People, Who knows, please, how usable are currently recursive module imports in Haskell, in GHC ? Is it essentially more difficult to `make' and support a project which has 50 modules, and half of all the module pairs import each other? Is recursive import in Haskell-98 ? Thank you in advance for explanation. ----------------- Serge Mechveliani mechvel(a)botik.ru

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ghci, sourcing
by Frederik Eaton 06 Jun '06

06 Jun '06

Hi, Is there a way to source a file in ghci? I have a series of initialization commands which I would like to run every time I do a certain set of experiments, and I've put them in a file. Is it best just to copy and paste the file into ghci? Frederik -- http://ofb.net/~frederik/

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recursive import
by Serge D. Mechveliani 06 Jun '06

06 Jun '06

Concering the current state of recursive import, Simon Peyton-Jones <simonpj(a)microsoft.com> writes on 5 Jun 2006 > [..] > > GHC's module-at-a-time compilation model means that GHC needs an hs-boot > file to "get started". The manual tries to explain what you can and > can't do. If you follow the rules it works pretty well. We use > recursive modules extensively for compiling GHC itself, and it's just > fine with 'make'. (ghc -M does the right thing.) > > [..] Thank you for the explanation. And how does this feature interact with packages, with making via Cabal ? Will Cabal work with recursive imports and with ghc-options: -fglasgow-exts -fallow-undecidable-instances -fallow-overlapping-instances -fno-warn-overlapping-patterns -fwarn-unused-binds -fwarn-unused-matches -fwarn-unused-imports -O -prof -auto-all ? Generally, I tend to use recursive modules because they simplify the global algorithm presentation. But fear of technical difficulties in the project support. Maybe, I would try this recursion. ----------------- Serge Mechveliani mechvel(a)botik.ru

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Bug? Or at least a better error message?
by Geoffrey Alan Washburn 05 Jun '06

05 Jun '06

While trying out the following example, in an attempt to learn something about the fiddly case where a type class instance tries to use an instance that is more specific than itself module Testing where class Foo a where { bar :: a -> Int } instance Foo Int where bar i = i instance Foo a => Foo [a] where bar [] = bar [1] bar ([x]) = 1 bar (x:xs) = (bar x) + (bar xs) It is kind of like polymorphic recursion, I suppose. I get the following exception [1 of 1] Compiling Testing ( strange.hs, interpreted ) *** Exception: typecheck/TcEnv.lhs:(365,0)-(392,32): Non-exhaustive patterns in function find_thing Is the example supposed to work? I'm trying to determine the source of a problem with type classes and GADTs and I figured this example using "normal" data types would be a good place to start in understanding what was going wrong. I was using ghci version 6.5.20060503.

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Data.Sequence?
by Michael Marte 02 Jun '06

02 Jun '06

Hello *, when importing Data.Queue in 6.4.2, I am told that it is deprecated and that I should use Data.Sequence instead. However, Data.Sequence is not part of the base package - it is there but it is missing from the package.conf file. Moreover, there is no documentation available apart from the source code itself. Regarding Data.Sequence itself: - I am missing a function for converting a sequence to a list directly; I have to create a view and convert it to a list. - Isn't the name too fuzzy? After all, a standard Haskell list is a sequence as well. Why not stay with Queue? Michael

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Understanding directory structure of ghc installation
by Brian Hulley 01 Jun '06

01 Jun '06

Hi - I've just downloaded and installed Edison using Cabal. However I now see that Edison seems to have been already installed with the ghc 6.4.2 installation, even though there's no mention of Edison in /doc/html/libraries/index.html, because there are old Edison .hi files in ghc-6.4.2/hslibs-imports/data whereas the Cabal install process copied newly built Edison files to C:\Program Files\Haskell\EdisonAPI-1.2\ghc-6.4.2\Data and C:\Program Files\Haskell\EdisonCore-1.2\ghc-6.4.2\Data I was about to just delete the old .hi files from the hslibs-imports/data directory, but then I noticed there are a few .hi files there for Set and FiniteMap, even though there are also .hi files (though of different sizes) for Set and FiniteMap stored in the imports/data directory as well. So my question is: how to understand all this? Why are there different copies of Set.hi which have different sizes, but in the same installation, and which one does ghc use when I use import Data.Set in a program? Also, what does .p_hi mean? (The new build of Edison only creates .hi files not .p_hi files but all the ghc-6.4.2 modules have both .hi and .p_hi files) (It would also be interesting to know where Cabal gets the information from to configure a package, and where the package database is stored...) Thanks, Brian. -- Logic empowers us and Love gives us purpose. Yet still phantoms restless for eras long past, congealed in the present in unthought forms, strive mightily unseen to destroy us. http://www.metamilk.com

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RE: GHC-6.4.1 on FreeBSD-amd64 port progress
by Simon Marlow 30 May '06

30 May '06

On 25 October 2005 10:01, Wilhelm B. Kloke wrote: > Simon Marlow <simonmar(a)microsoft.com> schrieb: >> On 24 October 2005 19:04, Wilhelm B. Kloke wrote: >> >> Is it that it does not find the libraries, or does it find the >> libraries but still gets a bunch of undefined references? If the >> latter, then there could be an issue with the mangler. Try an 'nm' >> on libHSbase.a to see if the missing symbols are actually defined. > > Nm shows that the problem may come from splitting. The missing symbols > are marked as locals (small d); being in different .o modules they > are not resolved. Try with splitting off: set SplitObjs=NO in your mk/build.mk. Cheers, Simon

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recompilation / overlapping instances
by Christian Maeder 29 May '06

29 May '06

Hallo Thomas, when compiling your sources in our context I get an "Overlapping instances" error (below). However, first compiling the offending file (base/TI/OrigTiMonad.hs) and then compiling the rest works (but I don't want adapt our Makefile for this to do). Could you adjust your sources? We're using ghc-6.4.2. Or is there a further compiler switch that would get this right? I don't know if both instances are identical. Cheers Christian ../programatica/tools/base/TI/OrigTiMonad.hs:61:36: Overlapping instances for Functor (Either (Error (HsIdentI i))) arising from use of `fmap' at ../programatica/tools/base/TI/OrigTiMonad.hs :61:36-39 Matching instances: Imported from Control.Monad.Error: instance Functor (Either e) ../programatica/tools/base/lib/Monads/ExceptM.hs:26:0: instance Functor (Either x) In a lambda abstraction: \ env ids -> fmap (fmap f) (m env ids) In the second argument of `($)', namely `\ env ids -> fmap (fmap f) (m env i ds)' In the definition of `fmap': fmap f (IM m) = IM $ (\ env ids -> ...)

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