Re: Type signature inside an instance declaration
Many thanks for your helps.
Kwanghoon
On Tue, Dec 16, 2008 at 11:22 PM, Thomas Schilling
nomin...@googlemail.comwrote:
{-# LANGUAGE ScopedTypeVariables #-}
2008/12/16 Neil Mitchell ndmitch...@gmail.com:
Hi
You want to use `asTypeOf`, with a lazy pattern to name a value of type
'a'.
pr xs = [ ++ pr (undefined `asTypeOf` x) ++ ]
where (x:_) = xs
I prefer:
pr xs = [ ++ pr (undefined `asTypeOf` head x) ++ ]
Or even more simply:
pr xs = [ ++ pr (head x) ++ ]
I do believe there is some GHC extension that can be turned on to
refer to variables like you did, but its not standard Haskell.
Thanks
Neil
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Re: Type signature inside an instance declaration
{-# LANGUAGE ScopedTypeVariables #-}
2008/12/16 Neil Mitchell ndmitch...@gmail.com:
Hi
You want to use `asTypeOf`, with a lazy pattern to name a value of type 'a'.
pr xs = [ ++ pr (undefined `asTypeOf` x) ++ ]
where (x:_) = xs
I prefer:
pr xs = [ ++ pr (undefined `asTypeOf` head x) ++ ]
Or even more simply:
pr xs = [ ++ pr (head x) ++ ]
I do believe there is some GHC extension that can be turned on to
refer to variables like you did, but its not standard Haskell.
Thanks
Neil
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Re: Type signature inside an instance declaration
Kwanghoon Choi lazysw...@gmail.com wrote: = instance Arg a = Arg [a] where pr _ = [ ++ pr (undefined :: a) ++ ] = You want to use `asTypeOf`, with a lazy pattern to name a value of type 'a'. pr xs = [ ++ pr (undefined `asTypeOf` x) ++ ] where (x:_) = xs or pr ~(x:_) = [ ++ pr (undefined `asTypeOf` x) ++ ] Regards, Malcolm ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: length of module name affecting performance??
Daniel Gorín wrote: On Dec 15, 2008, at 10:43 PM, Don Stewart wrote: dons: Running time as a function of module name length, http://galois.com/~dons/images/results.png 10 is the magic threshold, where indirections start creeping in. Codegen cost heuristic fail? Given this, could you open a bug ticket for it, with all the info we have, http://hackage.haskell.org/trac/ghc/newticket?type=bug E.g. the graph, the code, the asm diff. Cheers, Don done! http://hackage.haskell.org/trac/ghc/ticket/2884 I followed up on the ticket. Basically the problem is to do with inlining of record selectors: when the module name is too long, none of the record selectors get inlined. Cheers, Simon ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Type signature inside an instance declaration
=== module Test where class Arg a where pr :: a - String instance Arg Int where pr _ = i instance Arg Char where pr _ = c instance Arg a = Arg [a] where pr _ = [ ++ pr (undefined :: a) ++ ] -- the type variable 'a' is interpreted as an unbound one. -- (1) pr :: [a] - String -- (2) pr (_ :: [a]) = [ ++ pr (undefined :: a) ++ ] === Dear All, I got some problem when I try to compile the above program. The problem is due to the presence of a type variable 'a' in the body of the last instance declaration. How could I refer to the type variable of Arg [a] in the instance declaration? I tried these options 1) by giving an explicit declaration for pr 2) by giving a type signature to the argument of pr with -XPatternsSignatures The first option gives me back an error : Misplaced type signature: pr :: [a] - String The type signature must be given where `pr' is declared The second option gives me an error: Test.hs:21:12: Not in scope: type variable `a' Would anybody help me to understand this problem? Thanks in advance. Kwanghoon ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: Type signature inside an instance declaration
Hi You want to use `asTypeOf`, with a lazy pattern to name a value of type 'a'. pr xs = [ ++ pr (undefined `asTypeOf` x) ++ ] where (x:_) = xs I prefer: pr xs = [ ++ pr (undefined `asTypeOf` head x) ++ ] Or even more simply: pr xs = [ ++ pr (head x) ++ ] I do believe there is some GHC extension that can be turned on to refer to variables like you did, but its not standard Haskell. Thanks Neil ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: length of module name affecting performance??
I suddenly wonder if renaming Text.ParserCombinators.Parsec.Combinator would be a performance hack -- C ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: Can't compile GHC 6.8.2
Hello Barney all, I've been following your messages with some interest, as I too have been trying to build a more-modern ghc on my G3 iMac running 10.3.9. I started with an existing 6.6.1 build, and tried to build 6.8.3; I'm finally at the point where I have something to report, although I'm not sure if it's a success or a failure report... :-/ I applied your patch to package.conf.in (approximately; the relevant section wasn't quite identical), edited rts/Linker.c to add #define LC_SEGMENT_64 LC_SEGMENT, and hacked up a wrapper script around ar to always ranlib the library being processed; you had mentioned patching cabal, but I decided the wrapper around ar was easier... a hack, but what the hell. After that, configure make ran to completion without errors (although it took a couple of days, since I had all the extralibs). Success! ... or is it? I installed the new compiler into /usr/local, then tested it by trying ghc -v. Alas, no joy! It died with some dynamic-link error which I've approximately reproduced here: lupus:~/ghc-6.8.3% ghc-6.8.3 -v dyld: relocation error (external relocation for symbol _pthread_mutex_unlock in ghc-6.8.3 relocation entry 0 displacement too large)Trace/BPT trap Failure! ... or is it? I thought, how can this be?!? It built itself through stage2, it has to be good! But clearly it isn't... So I tried one last thing: I tried to use the stage1 compiler directly to compile the scheme interpreter I wrote nearly a year ago. That initially failed, too, but for a simple reason, and one I could work around: no readline in ghc 6.8.3. Once I changed the scheme interpreter to not use readline, it compiled, linked, and runs. So... success or failure? I'm really not quite sure... I guess I could try installing the stage1 compiler instead of the stage2 compiler, it seems that it might work. But it would appear that there is still something not entirely right in there. regards, Uwe ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
