[Haskell-cafe] Problems with GHC API and error handling
Hello, everyone.
I am in need of setting up custom exception handlers when using GHC
API to compile modules. Right now I have the following piece of code:
* Main.hs:
--
import GHC
import GHC.Paths
import MonadUtils
import Exception
import Panic
import Unsafe.Coerce
import System.IO.Unsafe
handleException :: (ExceptionMonad m, MonadIO m)
= m a - m (Either String a)
handleException m =
ghandle (\(ex :: SomeException) - return (Left (show ex))) $
handleGhcException (\ge - return (Left (showGhcException ge ))) $
flip gfinally (liftIO restoreHandlers) $
m = return . Right
initGhc :: Ghc ()
initGhc = do
dfs - getSessionDynFlags
setSessionDynFlags $ dfs { hscTarget = HscInterpreted
, ghcLink = LinkInMemory }
return ()
test :: IO (Either String Int)
test = handleException $ runGhc (Just libdir) $ do
initGhc
setTargets = sequence [ guessTarget ./test/file1.hs Nothing ]
graph - depanal [] False
loaded - load LoadAllTargets
-- when (failed loaded) $ throw LoadingException
setContext (map (IIModule . moduleName . ms_mod) graph)
let expr = main
ty - exprType expr -- throws exception if doesn't typecheck
output ty
res - unsafePerformIO . unsafeCoerce $ compileExpr expr
return res
--
* file1.hs:
module Main where
main = do
return x
The problem is when I run the 'test' function above I receive the
following output:
h test
test/file1.hs:4:10: Not in scope: `x'
Left Cannot add module Main to context: not a home module
it :: Either String Int
So, if I understand this correctly, my exception handler does indeed
catch an exception correctly,
however, I still receive some output which I want to be captured.
Is there a way to do this?
--
Sincerely yours,
-- Daniil Frumin
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell Platform 2013.2.0.0 64bit.pkg
As a side note, I have stopped having cabal issues since I started using hsenv. It sandboxes packages for you. So if you have install problems you just need to delete a local .hsenv directory instead of reinstalling everything. On Jun 12, 2013 11:15 PM, Richard A. O'Keefe o...@cs.otago.ac.nz wrote: My original problem was that I wanted to load a particular set of packages using 'cabal install'. It didn't work (cabal install issues) and while the maintainer reacted promptly and helpfully, cabal kept on trying to install the wrong version. Part of the problem was that blasting away ~/.cabal and ~/Library/Haskell wasn't enough: it's necessary to blast away ~/.ghc as well (which I had forgotten existed and of course never saw). * It would be handy if 'uninstall-hs' had an option, say * uninstall-hs --user * so that a user could in one step make it as if they had never * used the Haskell Platform. (Sigh. Changes to the GHC command line interface since 7.0 have broken one of the packages I used to have installed, and the maintainer's e-mail address doesn't work any more. And sometimes it seems as if every time I install anything with cabal something else breaks.) PS. Earlier today cabal gave me some confusing messages which turned out to mean 'GSL isn't installed'. Non-Haskell dependencies could be explained a little more clearly. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Improved ghc-pkg cache warnings
When ghc-pkg observes your cache is out of date, it displays a helpful warning, recommending ghc-pkg recache. However, sometimes running this command does not fix the problem, because it targets the wrong cache. For out of date global caches, ghc-pkg --global recache successfully clears the warning. For out of date user caches, ghc-pkg --user recache clears the warning. In the future, could ghc-pkg display the command more specific to the problem? -- Cheers, Andrew Pennebaker www.yellosoft.us ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Efficiency/Evaluation Question
I'm working through some beginner-level keyboard problems I found at users.csc.calpoly.edu. One problem is the Saddle Points problem: quote: Write a program to search for the saddle points in a 5 by 5 array of integers. A saddle point is a cell whose value is greater than or equal to any in its row, and less than or equal to any in its column. There may be more than one saddle point in the array. Print out the coordinates of any saddle points your program finds. Print out No saddle points if there are none. Let's say I use a simple list grid like so: code: array = Grid 5 [ [1,5,3,6,4] , [8,2,6,3,8] , [3,8,7,2,9] , [0,3,7,1,2] , [7,2,7,4,5] ] data Grid = Grid Int [[Int]] And let's say I take a brute force approach, moving through each cell, checking to see if it is the greatest in its row and the least in its column. And say I have functions like so for getting rows and columns: code: row (Grid s l) n = if (n = s) then [] else l !! n col g@(Grid s l) n = if (n = s) then [] else col_ g n 0 where col_ (Grid s l) n i = if (i = s) then [] else (head l !! n) : col_ (Grid s (tail l)) n (i + 1) My question: With the way Haskell works (thunks, lazy evaluation, and all that mystery), is it actually worth the trouble of /precalculating/ the maximum row values and minimum column values, to compare cell values against? Or will, for example, something like (smallest_list_value (col array 1)) definitely only evaluate once? -- frigidcode.com signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Efficiency/Evaluation Question
I expect you'll get many replies... row (Grid s l) n = if (n = s) then [] else l !! n col g@(Grid s l) n = if (n = s) then [] else col_ g n 0 where col_ (Grid s l) n i = if (i = s) then [] else (head l !! n) : col_ (Grid s (tail l)) n (i + 1) While such low-level approach (focus on the element) can certainly be made to work, but Haskell encourages you to think in higher level constructs. I haven't seen this problem before but I would map the original array from [[Int]] - [(Int, (Int, Int), Int, Int)], that is: a list of tuples consisting of the original element, its coordinate, the row maximum and the column minimum. From there its a trivial filter to find your results. (I'm sure there's a more elegant solution). My question: With the way Haskell works (thunks, lazy evaluation, and all that mystery), is it actually worth the trouble of /precalculating/ the maximum row values and minimum column values, to compare cell values against? Or will, for example, something like (smallest_list_value (col array 1)) definitely only evaluate once? There's not enough context to answer the specific question, but lazy evaluation isn't magic and the answer is probably no. Tommy ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Efficiency/Evaluation Question
On 06/15/2013 04:39 PM, Tommy Thorn wrote:
There's not enough context to answer the specific question,
but lazy evaluation isn't magic and the answer is probably no.
Tommy
Perhaps to simplify the question somewhat with a simpler example.
Suppose you have
code:
let f x = if (x 4) then f 0 else (sin x + 2 * cos x) : f (x + 1)
After calculating at x={0,1,2,3}, and the cycle repeats, are sin, cos,
etc. calculated anymore?
--
frigidcode.com
signature.asc
Description: OpenPGP digital signature
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Efficiency/Evaluation Question
On 06/15/2013 05:02 PM, Christopher Howard wrote:
On 06/15/2013 04:39 PM, Tommy Thorn wrote:
Perhaps to simplify the question somewhat with a simpler example.
Suppose you have
code:
let f x = if (x 4) then f 0 else (sin x + 2 * cos x) : f (x + 1)
After calculating at x={0,1,2,3}, and the cycle repeats, are sin, cos,
etc. calculated anymore?
That might have been ambiguous. What I meant was:
code:
let f x = if (x 4) then f 0 else (sin x + 2 * cos x) : f (x + 1)
If I calculate (f 0), and the cycle repeats after four values, are sin,
cos, etc. calculated anymore?
--
frigidcode.com
signature.asc
Description: OpenPGP digital signature
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Efficiency/Evaluation Question
Yes. In general, GHC won't CSE for you.
- Clark
On Saturday, June 15, 2013, Christopher Howard wrote:
On 06/15/2013 04:39 PM, Tommy Thorn wrote:
There's not enough context to answer the specific question,
but lazy evaluation isn't magic and the answer is probably no.
Tommy
Perhaps to simplify the question somewhat with a simpler example.
Suppose you have
code:
let f x = if (x 4) then f 0 else (sin x + 2 * cos x) : f (x + 1)
After calculating at x={0,1,2,3}, and the cycle repeats, are sin, cos,
etc. calculated anymore?
--
frigidcode.com
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Efficiency/Evaluation Question
There's a very good StackOverflow question which covers this: When is
memoization automatic in GHC?[1]. I found it really cleared up the issue
for me.
[1]:
http://stackoverflow.com/questions/3951012/when-is-memoization-automatic-in-ghc-haskell
On Sat, Jun 15, 2013 at 9:13 PM, Clark Gaebel cgae...@uwaterloo.ca wrote:
Yes. In general, GHC won't CSE for you.
- Clark
On Saturday, June 15, 2013, Christopher Howard wrote:
On 06/15/2013 04:39 PM, Tommy Thorn wrote:
There's not enough context to answer the specific question,
but lazy evaluation isn't magic and the answer is probably no.
Tommy
Perhaps to simplify the question somewhat with a simpler example.
Suppose you have
code:
let f x = if (x 4) then f 0 else (sin x + 2 * cos x) : f (x + 1)
After calculating at x={0,1,2,3}, and the cycle repeats, are sin, cos,
etc. calculated anymore?
--
frigidcode.com
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
