December 2007 - Haskell-Cafe

Re: ANNOUNCE: GHC version 6.8.2
by John Dorsey 21 Dec '07

21 Dec '07

(Moving to the cafe) On a related topic, I've been trying to build 6.8.2 on Leopard lately. I've been running up against the infamous OS X readline issues. I know some builders here have hacked past it, but I'm looking for a good workaround... ideally one that works without changes outside the GHC build area (besides installing a real readline). Here's what I noticed before I started drowning in the build platform. (I'm no gnu-configure expert nor GHC insider.) I can get gnu-readline installed from Macports, no problem. The top-level configure in GHC doesn't respond to my various attempts: o using --with-readline-libraries and --with-readline-includes (Although it looks like the libraries/readline/configure script might recognize these, I can't get an option to pass through.) o setting LDFLAGS and CPPFLAGS environment variables (with -L/opt/local/lib and -I/opt/local/include resp.) in my shell before running configure o playing with the above settings and others in a mk/build.mk Until Apple fixes their broken-readline issue (maybe when the readline compatibility of libedit improves)... maybe the top-level configure can pass through flags or settings somehow? For those who've built with readline on OS X: have you had to resort to blasting the existing readline library link, or is there a configuration option within the GHC tree that you've gotten to work? Should I be filing a trac bug instead of asking here? Thanks for any help. There's no urgency for me; I'm just trying to get a working environment at home; I'd prefer to be able to bootstrap from the ground up; and I'd like to be able to contribute to testing/debugging on OSX. John

1 0

functional maps
by Chad Scherrer 21 Dec '07

21 Dec '07

A while back I was playing with Data.Map was getting irritated about lookups that fail having the type of values, but wrapped in an extra monad. I decided to work around this by putting a default in the data type itself, so we have a "functional map" data FMap k a = FMap (k -> a) (Map k a) This has been really convenient - it's a monad, and failed lookups have the same type as successful ones. lookup :: (Ord k) => k -> FMap k a -> a lookup k (FMap f m)= Map.findWithDefault (f k) k m This also makes it much nicer to build a function that tabulates a list of pairs (nicer than I've found using Data.Map, anyway): fromPairs :: (Ord k) => [(k,a)] -> FMap k [a] fromPairs = foldl' (flip . uncurry $ insertWith (:)) $ return [] insertWith :: (Ord k) => (a -> b -> b) -> k -> a -> FMap k b -> FMap k b insertWith f k x m = case lookup k m of v -> insert k (f x v) m Ok, great, but fromPairs is blowing the stack. It does fine for a while, but today I was trying to use it for a few million pairs. It runs for a while, eats a couple gigs of ram, and then I get a stack overflow. Any advice for tracking this down? Thanks! Chad

1 1

How to make Prelude.read: no parse more verbose ...
by Georg Sauthoff 21 Dec '07

21 Dec '07

Hi, I try to debug some existing Haskell-Code. Out of the blue I get a 'progname: Prelude.read: no parse' error message from GHC. Great. Well, the code includes # grep '\<read\>' *| wc -l 23 (sic!) calls to the read fn. Well, how do I compile a Haskell program in such a way, that I get a useful error message from read? I mean, like the filename/linenumber of the calling expression for starters. Really crazy would be the possibility to print out a backtrace, if some (library) function calls error ... Best regards Georg -- Fortune : 'Real programmers don't comment their code. It was hard to write, it should be hard to understand.' ;)

6 6

Applying a Dynamic function to a container of Dynamics
by Alfonso Acosta 21 Dec '07

21 Dec '07

Hi all, dynApp allows to apply a Dynamic function to a Dynamic argument: dynApp :: Dynamic -> Dynamic -> Dynamic I don't seem to find a way (without modifying Data.Dynamic itself) to code this function import Data.Typeable import Data.Dynamic import Data.Foldable dynApp1 :: (Typeable1 container, Foldable container) => Dynamic -> container Dynamic -> Dynamic dynApp1 f -- originally of type :: container a -> b val --- all its values _must_ have type :: b -- I get stuck when trying to transform val to type Dynamic (transform :: container Dynamic -> Dynamic) in order to apply f nor even the more concrete case of lists dynAppList :: Dynamic -> [Dynamic] -> Dynamic Any suggestions? Thanks, Fons

1 0

Smart Constructor Puzzle
by Ronald Guida 21 Dec '07

21 Dec '07

I'm playing around with smart constructors, and I have encountered a weird puzzle. My goal is to do vector arithmetic. I'm using smart constructors so that I can store a vector as a list and use the type system to staticly enforce the length of a vector. So my first step is to define Peano numbers at the type level. > data PZero = PZero deriving (Show) > data PSucc a = PSucc a deriving (Show) > > type P1 = PSucc PZero > type P2 = PSucc P1 > type P3 = PSucc P2 > -- etc Next, I define a vector type and tag it with a Peano number. > data Vec s t = Vec [t] deriving (Eq, Ord, Show, Read) Now I can define a few smart constructors. > vec0 :: Vec PZero t > vec0 = Vec [] > > vec1 :: t -> Vec P1 t > vec1 x = Vec [x] > > vec2 :: t -> t -> Vec P2 t > vec2 x y = Vec [x, y] > > vec3 :: t -> t -> t -> Vec P3 t > vec3 x y z = Vec [x, y, z] Now here's the puzzle. I want to create a function "vecLength" that accepts a vector and returns its length. The catch is that I want to calculate the length based on the /type/ of the vector, without looking at the number of elements in the list. So I started by defining a class that allows me to convert a Peano number to an integer. I couldn't figure out how to define a function that converts the type directly to an integer, so I am using a two-step process. Given a Peano type /t/, I would use the expression "pToInt (pGetValue :: t)". > class Peano t where > pGetValue :: t > pToInt :: t -> Int > > instance Peano PZero where > pGetValue = PZero > pToInt _ = 0 > > instance (Peano t) => Peano (PSucc t) where > pGetValue = PSucc pGetValue > pToInt (PSucc a) = 1 + pToInt a Finally, I tried to define vecLength, but I am getting an error. > vecLength :: (Peano s) => Vec s t -> Int > vecLength _ = pToInt (pGetValue :: s) < Could not deduce (Peano s1) from the context () < arising from a use of `pGetValue' < Possible fix: < add (Peano s1) to the context of the polymorphic type `forall s. s' < In the first argument of `pToInt', namely `(pGetValue :: s)' < In the expression: pToInt (pGetValue :: s) < In the definition of `vecLength': < vecLength _ = pToInt (pGetValue :: s) Any suggestions? -- Ron

5 4

upgrading regex in GHC 6.8.2
by Michael Mounteney 21 Dec '07

21 Dec '07

Hello, I have an application that uses/used Text.Regex and have just updated GHC from 6.6.1 to 6.8.2 and it seems that Text.Regex is gone, so I'm trying to install the replacement from Hackage. First of all, the procedure is quite tedious as one has to install the hierarchy of dependencies manually but apparently there are moves to automate this process. The procedure stalled on regex-base-0.92. I fixed the build-depends in regex-base.cabal to: Build-Depends: base >= 2.0, mtl, containers >= 0.1.0.1, bytestring, array following information I found via an internet search but on runghc Setup.hs install it says: Setup.hs: Error: Could not find module: Text.Regex.Base with any suffix: ["hi"] It seems that it is necessary to remove the Text.Regex.Base and Text.Regex.Base.Impl entries from the Exposed-Modules: line but then regex-posix build complains that it can't find Text.Regex.Base. I tried various hackery like compiling Text/Regex/Base.hs manually but even when Text/Regex/Base.hi exists, the runghc Setup.hs install error message above still occurs. What is happening ? -- _________________________________ Michael Mounteney,+618 4311 11547

3 2

Is there some place where I can find the hs-curses doc ?
by david48 20 Dec '07

20 Dec '07

It seems I can't find it. David.

3 3

instance Monad Either?
by Eric 20 Dec '07

20 Dec '07

According to this <http://www.randomhacks.net/articles/2007/03/10/haskell-8-ways-to-report-err…> Either is an instance of class Monad, but when I try to use the do notation I get a compiler error. What's going on? E.

4 4

[RFC] Preliminary benchmark graphs
by Peter Lund 20 Dec '07

20 Dec '07

I added Don's three benchmarks and redid all my benchmarks with: ghc 6.6.1 ghc 6.8.2 ghc 6.8.2 + bytestring 0.9.0.2 ghc 6.9.20071119 ghc 6.9.20071119 + bytestring 0.9.0.2 ghc head-as-of-yesterday-around-noon ghc head-as-of-yesterday-around-noon + bytestring 0.9.0.2 I tried to get the draft emails with intro, methodology, discussion, and conclusion completed yesterday but my brain simply wasn't up to it. Unfortunately, it still isn't quite up to it :( Since the perfect is the enemy of the good, I'll post the graphs for all the above 7 runs now. The rest will be forthcoming when I can think straight again, hopefully some time in the evening. I have scripts to help me install precisely the ghc version I want (and to make it easy to duplicate my results). I also have scripts to run the benchmarks, get correct memory measurements (-sstderr doesn't seem trustworthy), check the validity of each timing measurement, generate I/O traces, generate reports, and finally merging reports from different runs with or without rescaling. This attached report uses rescaling since I'm compiling different compiler/library combinations on the same machine. One thing that shows up very clearly in the graphs is that the memory situation is bad and that Don's recent fix only really solves the problem on 6.8.2, not on head. Another thing is that the backend really lets us down. I have hand-tweaked a simple byte counting benchmark and a simple space counting benchmark through increasing degrees of refinement from the banal to the heroic and timed those, too. It seems like improved register use alone would halve the run time. Add a sprinkling of MMX heroics and things get even better (but that's not realistic or even a good idea at the moment). The reason why lazy bytestrings perform so badly, speed-wise, is most likely a backend that doesn't do hoisting of "bounds checks" out of loops. -Peter charybdis ghc 6.6.1 AMD Athlon(tm) 64 Processor 3000+ 2009.160 MHz TESTKIND=THOROUGH SUFFIX= charybdis ghc 6.8.2 AMD Athlon(tm) 64 Processor 3000+ 2009.160 MHz TESTKIND=THOROUGH SUFFIX= charybdis ghc 6.8.2 AMD Athlon(tm) 64 Processor 3000+ 2009.160 MHz TESTKIND=THOROUGH SUFFIX=-bs0.9.0.2 charybdis ghc 6.9.20071119 AMD Athlon(tm) 64 Processor 3000+ 2009.160 MHz TESTKIND=THOROUGH SUFFIX= charybdis ghc 6.9.20071119 AMD Athlon(tm) 64 Processor 3000+ 2009.160 MHz TESTKIND=THOROUGH SUFFIX=-bs0.9.0.2 charybdis ghc 6.9.20071217 AMD Athlon(tm) 64 Processor 3000+ 2009.160 MHz TESTKIND=THOROUGH SUFFIX= charybdis ghc 6.9.20071217 AMD Athlon(tm) 64 Processor 3000+ 2009.160 MHz TESTKIND=THOROUGH SUFFIX=-bs0.9.0.2 Time (byte counting) std -------------------- avg dev slack hs/byte-bs----acc: 1.020 40‰ 0.0 █████▏ | -- 0.703 5‰ 0.4 ███▌ | -- 0.702 7‰ 0.3 ███▌ | -- 0.705 7‰ 0.1 ███▋ | -- 0.712 3‰ 0.1 ███▋ | -- 0.706 7‰ 0.1 ███▋ | -- 0.707 7‰ 0.9 ███▋ | hs/byte-bs----foldlx: 0.789 3‰ 0.3 ████ | -- 0.993 2‰ 0.2 █████ | -- 1.102 1‰ 0.2 █████▋ | -- 1.002 1‰ 0.5 █████▏ | -- 1.112 1‰ 0.3 █████▋ | -- 1.024 2‰ 0.2 █████▏ | -- 1.111 1‰ 0.1 █████▋ | hs/byte-bs----foldrx: 0.813 3‰ 0.1 ████▏ | -- 1.102 2‰ 0.3 █████▋ | -- 1.100 1‰ 0.1 █████▋ | -- 1.112 2‰ 0.1 █████▋ | -- 1.114 1‰ 0.4 █████▋ | -- 1.113 2‰ 0.5 █████▋ | -- 1.112 1‰ 0.2 █████▋ | hs/byte-bsl---acc: 3.599 13‰ 0.0 ██████████████████▎ | -- 2.609 17‰ 0.0 █████████████▎ | -- 2.560 15‰ 0.1 █████████████ | -- 2.595 14‰ 0.1 █████████████▏ | -- 2.574 16‰ 0.1 █████████████ | -- 2.613 12‰ 0.2 █████████████▎ | -- 2.656 44‰ 0.1 █████████████▌ | hs/byte-xxxxx-acc-1: 4.606 5‰ 0.0 ███████████████████████▍ | -- 4.730 3‰ 0.0 ████████████████████████ | -- 4.722 3‰ 0.1 ███████████████████████▉ | -- 4.436 5‰ 0.0 ██████████████████████▌ | -- 4.500 6‰ 0.1 ██████████████████████▊ | -- 4.462 4‰ 0.1 ██████████████████████▋ | -- 4.499 7‰ 0.1 ██████████████████████▊ | hs/byte-xxxxx-acc-2: 4.595 5‰ 0.0 ███████████████████████▎ | -- 4.704 1‰ 0.0 ███████████████████████▉ | -- 4.722 6‰ 0.0 ███████████████████████▉ | -- 4.473 8‰ 0.0 ██████████████████████▋ | -- 4.493 5‰ 0.0 ██████████████████████▊ | -- 4.477 3‰ 0.1 ██████████████████████▋ | -- 4.446 2‰ 0.0 ██████████████████████▌ | hs/byte-xxxxx-foldl: 4.566 9‰ 0.0 ███████████████████████▏ | -- 4.754 6‰ 0.1 ████████████████████████▏ | -- 4.735 7‰ 0.0 ████████████████████████ | -- 4.412 10‰ 0.0 ██████████████████████▍ | -- 4.486 3‰ 0.0 ██████████████████████▊ | -- 4.473 3‰ 0.0 ██████████████████████▋ | -- 4.511 10‰ 0.1 ██████████████████████▉ | Memory: Peak ------- KB hs/byte-bs----acc: 147448 ████████████████████████████████████████ | -- 147500 ████████████████████████████████████████ | -- 147616 ████████████████████████████████████████ | -- 147752 ████████████████████████████████████████ | -- 147732 ████████████████████████████████████████ | -- 147772 ████████████████████████████████████████ | -- 147780 ████████████████████████████████████████ | hs/byte-bs----foldlx: 147468 ████████████████████████████████████████ | -- 147528 ████████████████████████████████████████ | -- 147624 ████████████████████████████████████████ | -- 147748 ████████████████████████████████████████ | -- 147736 ████████████████████████████████████████ | -- 147796 ████████████████████████████████████████▏ | -- 147780 ████████████████████████████████████████ | hs/byte-bs----foldrx: 147452 ████████████████████████████████████████ | -- 147500 ████████████████████████████████████████ | -- 147624 ████████████████████████████████████████ | -- 147744 ████████████████████████████████████████ | -- 147740 ████████████████████████████████████████ | -- 147772 ████████████████████████████████████████ | -- 147784 ████████████████████████████████████████ | hs/byte-bsl---acc: 2872 ▊ | -- 2920 ▊ | -- 3040 ▉ | -- 3172 ▉ | -- 3184 ▉ | -- 3212 ▉ | -- 3216 ▉ | hs/byte-xxxxx-acc-1: 1572 ▍ | -- 1632 ▌ | -- 1636 ▌ | -- 1904 ▌ | -- 1904 ▌ | -- 1900 ▌ | -- 1900 ▌ | hs/byte-xxxxx-acc-2: 1568 ▍ | -- 1636 ▌ | -- 1636 ▌ | -- 1904 ▌ | -- 1900 ▌ | -- 1900 ▌ | -- 1896 ▌ | hs/byte-xxxxx-foldl: 1572 ▍ | -- 1632 ▌ | -- 1636 ▌ | -- 1900 ▌ | -- 1904 ▌ | -- 1900 ▌ | -- 1896 ▌ | Time (space counting) std --------------------- avg dev slack hs/space-bs-c8-acc-1: 1.287 20‰ 0.2 ██████▌ | -- 1.131 2‰ 0.1 █████▊ | -- 1.132 2‰ 0.3 █████▊ | -- 1.145 1‰ 0.2 █████▊ | -- 1.150 1‰ 0.2 █████▉ | -- 1.147 2‰ 0.1 █████▊ | -- 1.147 2‰ 0.2 █████▊ | hs/space-bs-c8-count: 0.770 2‰ 0.0 ███▉ | -- 0.711 1‰ 0.4 ███▋ | -- 0.513 2‰ 0.2 ██▋ | -- 0.521 1‰ 0.2 ██▋ | -- 0.523 3‰ 0.2 ██▋ | -- 0.522 5‰ 0.2 ██▋ | -- 0.523 3‰ 0.6 ██▋ | hs/space-bs-c8-foldlx-1: 1.272 1‰ 0.2 ██████▌ | -- 1.205 2‰ 0.2 ██████▏ | -- 1.164 3‰ 0.0 █████▉ | -- 1.221 1‰ 0.1 ██████▏ | -- 1.176 1‰ 0.3 ██████ | -- 1.259 1‰ 0.1 ██████▍ | -- 1.176 1‰ 0.2 ██████ | hs/space-bs-c8-foldlx-2: 1.270 1‰ 0.2 ██████▍ | -- 1.207 1‰ 0.2 ██████▏ | -- 1.165 2‰ 0.1 █████▉ | -- 1.219 2‰ 0.2 ██████▏ | -- 1.176 1‰ 0.3 ██████ | -- 1.258 1‰ 0.2 ██████▍ | -- 1.177 1‰ 0.2 ██████ | hs/space-bs-c8-foldrx: 1.064 2‰ 0.1 █████▍ | -- 1.168 2‰ 0.2 █████▉ | -- 1.164 1‰ 0.3 █████▉ | -- 1.172 2‰ 0.3 █████▉ | -- 1.177 1‰ 0.2 ██████ | -- 1.176 1‰ 0.2 ██████ | -- 1.176 1‰ 0.1 ██████ | hs/space-bs-c8-lenfil: 1.271 1‰ 0.1 ██████▍ | -- 1.218 1‰ 0.2 ██████▏ | -- 0.541 3‰ 0.2 ██▊ | -- 1.223 1‰ 0.2 ██████▎ | -- 0.549 1‰ 0.4 ██▊ | -- 1.225 1‰ 0.2 ██████▎ | -- 0.551 5‰ 0.4 ██▊ | hs/space-bslc8-acc-1: 6.367 17‰ 0.2 ████████████████████████████████▎ | -- 3.396 7‰ 0.1 █████████████████▎ | -- 3.508 4‰ 0.1 █████████████████▊ | -- 3.388 10‰ 0.1 █████████████████▏ | -- 3.441 10‰ 0.1 █████████████████▍ | -- 3.438 3‰ 0.0 █████████████████▍ | -- 3.434 13‰ 0.1 █████████████████▍ | hs/space-bslc8-acc-2: 6.150 21‰ 0.0 ███████████████████████████████▏ | -- 3.470 5‰ 0.0 █████████████████▋ | -- 3.439 10‰ 0.1 █████████████████▍ | -- 3.386 5‰ 0.1 █████████████████▏ | -- 3.479 11‰ 0.1 █████████████████▋ | -- 3.467 6‰ 0.1 █████████████████▌ | -- 3.470 10‰ 0.1 █████████████████▋ | hs/space-bslc8-acc-3: 4.041 21‰ 0.1 ████████████████████▌ | -- 2.959 13‰ 0.0 ███████████████ | -- 2.920 16‰ 0.1 ██████████████▊ | -- 2.832 4‰ 0.1 ██████████████▍ | -- 2.925 14‰ 0.1 ██████████████▊ | -- 2.987 9‰ 0.0 ███████████████▏ | -- 2.996 20‰ 0.1 ███████████████▏ | hs/space-bslc8-count: 0.713 1‰ 0.3 ███▋ | -- 0.735 1‰ 0.4 ███▊ | -- 0.431 0‰ 0.7 ██▏ | -- 0.477 2‰ 0.4 ██▍ | -- 0.482 1‰ 0.4 ██▌ | -- 0.479 1‰ 0.6 ██▍ | -- 0.482 2‰ 0.4 ██▌ | hs/space-bslc8-foldl: 1.431 1‰ 0.3 ███████▎ | -- 1.398 1‰ 0.2 ███████▏ | -- 1.197 1‰ 0.2 ██████ | -- 1.458 1‰ 0.3 ███████▍ | -- 1.059 0‰ 0.0 █████▍ | -- 1.459 1‰ 0.1 ███████▍ | -- 1.061 0‰ 0.4 █████▍ | hs/space-bslc8-foldlx-1: 1.430 1‰ 0.1 ███████▎ | -- 1.400 1‰ 0.1 ███████▏ | -- 1.197 1‰ 0.0 ██████ | -- 1.458 0‰ 0.1 ███████▍ | -- 1.060 1‰ 0.0 █████▍ | -- 1.457 1‰ 0.1 ███████▍ | -- 1.060 1‰ 0.2 █████▍ | hs/space-bslc8-foldlx-2: 1.431 1‰ 0.1 ███████▎ | -- 1.399 1‰ 0.1 ███████▏ | -- 1.196 1‰ 0.1 ██████ | -- 1.457 1‰ 0.1 ███████▍ | -- 1.060 1‰ 0.3 █████▍ | -- 1.458 1‰ 0.1 ███████▍ | -- 1.060 1‰ 0.0 █████▍ | hs/space-bslc8-foldr-1: 1.748 1‰ 0.0 ████████▉ | -- 1.579 2‰ 0.1 ████████ | -- 1.220 2‰ 0.2 ██████▏ | -- 1.312 1‰ 0.2 ██████▋ | -- 1.213 1‰ 0.2 ██████▏ | -- 1.325 4‰ 0.2 ██████▊ | -- 1.213 2‰ 0.2 ██████▏ | hs/space-bslc8-foldr-2: 1.745 1‰ 0.1 ████████▉ | -- 1.579 2‰ 0.1 ████████ | -- 1.220 1‰ 0.2 ██████▏ | -- 1.315 1‰ 0.2 ██████▋ | -- 1.210 1‰ 0.2 ██████▏ | -- 1.317 4‰ 0.2 ██████▋ | -- 1.213 2‰ 0.2 ██████▏ | hs/space-bslc8-lenfil-1: 1.521 7‰ 0.2 ███████▊ | -- 1.295 1‰ 0.2 ██████▌ | -- 0.429 0‰ 0.2 ██▏ | -- 1.323 1‰ 0.1 ██████▊ | -- 0.483 2‰ 0.4 ██▌ | -- 1.327 1‰ 0.2 ██████▊ | -- 0.482 2‰ 0.4 ██▌ | hs/space-bslc8-lenfil-2: 1.532 6‰ 0.1 ███████▊ | -- 1.296 0‰ 0.0 ██████▌ | -- 0.429 0‰ 0.2 ██▏ | -- 1.325 1‰ 0.1 ██████▊ | -- 0.483 1‰ 0.6 ██▌ | -- 1.327 1‰ 0.2 ██████▊ | -- 0.482 2‰ 0.4 ██▌ | hs/space-bsl---foldlx: 1.288 1‰ 0.2 ██████▌ | -- 1.333 1‰ 0.0 ██████▊ | -- 1.168 1‰ 0.2 █████▉ | -- 1.391 1‰ 0.1 ███████ | -- 1.006 1‰ 0.3 █████▏ | -- 1.395 1‰ 0.1 ███████▏ | -- 1.008 1‰ 0.2 █████▏ | hs/space-xxxxx-acc-1: 5.036 7‰ 0.1 █████████████████████████▌ | -- 5.381 6‰ 0.0 ███████████████████████████▎ | -- 5.358 8‰ 0.1 ███████████████████████████▏ | -- 4.991 1‰ 0.1 █████████████████████████▎ | -- 5.047 7‰ 0.1 █████████████████████████▌ | -- 5.051 3‰ 0.1 █████████████████████████▋ | -- 5.049 4‰ 0.1 █████████████████████████▋ | hs/space-xxxxx-acc-2: 5.009 7‰ 0.1 █████████████████████████▍ | -- 5.437 4‰ 0.1 ███████████████████████████▌ | -- 5.406 2‰ 0.0 ███████████████████████████▍ | -- 4.985 1‰ 0.0 █████████████████████████▎ | -- 5.057 4‰ 0.1 █████████████████████████▋ | -- 5.048 6‰ 0.1 █████████████████████████▌ | -- 5.089 6‰ 0.0 █████████████████████████▊ | hs/space-xxxxx-foldl: 5.024 5‰ 0.0 █████████████████████████▌ | -- 5.371 9‰ 0.0 ███████████████████████████▎ | -- 5.301 9‰ 0.1 ██████████████████████████▉ | -- 5.035 2‰ 0.1 █████████████████████████▌ | -- 5.037 3‰ 0.0 █████████████████████████▌ | -- 5.046 4‰ 0.0 █████████████████████████▌ | -- 5.042 4‰ 0.0 █████████████████████████▌ | hs/space-xxxxx-lenfil: 7.042 4‰ 0.0 ███████████████████████████████████▋ | -- 7.505 3‰ 0.0 ██████████████████████████████████████| -- 7.498 3‰ 0.0 ██████████████████████████████████████| -- 7.106 8‰ 0.1 ████████████████████████████████████ | -- 7.092 3‰ 0.1 ███████████████████████████████████▉ | -- 7.083 3‰ 0.0 ███████████████████████████████████▉ | -- 7.121 5‰ 0.1 ████████████████████████████████████ | hs/space-bslc8-chunk-1: n/a -- 1.054 0‰ 0.3 █████▍ | -- 1.053 1‰ 0.1 █████▍ | -- 1.094 0‰ 0.3 █████▌ | -- 1.088 0‰ 0.0 █████▌ | -- 1.096 1‰ 0.1 █████▌ | -- 1.089 0‰ 0.6 █████▌ | hs/space-bslc8-chunk-2: n/a -- 1.055 0‰ 0.3 █████▍ | -- 1.053 0‰ 0.1 █████▍ | -- 1.094 1‰ 0.3 █████▌ | -- 1.088 1‰ 0.2 █████▌ | -- 1.096 1‰ 0.2 █████▌ | -- 1.089 0‰ 0.1 █████▌ | hs/space-bslc8-chunk-3: n/a -- 1.190 4‰ 0.2 ██████ | -- 1.199 1‰ 0.3 ██████▏ | -- 1.087 1‰ 0.3 █████▌ | -- 1.051 1‰ 0.4 █████▍ | -- 1.077 1‰ 0.1 █████▌ | -- 1.053 1‰ 0.2 █████▍ | hs/space-bslc8-chunk-4: n/a -- 1.054 0‰ 0.2 █████▍ | -- 1.054 0‰ 0.2 █████▍ | -- 1.099 0‰ 0.3 █████▋ | -- 1.097 1‰ 0.1 █████▌ | -- 1.094 1‰ 0.2 █████▌ | -- 1.096 0‰ 0.0 █████▌ | Memory: Peak ------- KB hs/space-bs-c8-acc-1: 147448 ████████████████████████████████████████ | -- 147492 ████████████████████████████████████████ | -- 147608 ████████████████████████████████████████ | -- 147736 ████████████████████████████████████████ | -- 147740 ████████████████████████████████████████ | -- 147752 ████████████████████████████████████████ | -- 147752 ████████████████████████████████████████ | hs/space-bs-c8-count: 147448 ████████████████████████████████████████ | -- 147500 ████████████████████████████████████████ | -- 147612 ████████████████████████████████████████ | -- 147744 ████████████████████████████████████████ | -- 147756 ████████████████████████████████████████ | -- 147764 ████████████████████████████████████████ | -- 147776 ████████████████████████████████████████ | hs/space-bs-c8-foldlx-1: 147468 ████████████████████████████████████████ | -- 147524 ████████████████████████████████████████ | -- 147608 ████████████████████████████████████████ | -- 147756 ████████████████████████████████████████ | -- 147744 ████████████████████████████████████████ | -- 147796 ████████████████████████████████████████▏ | -- 147752 ████████████████████████████████████████ | hs/space-bs-c8-foldlx-2: 147468 ████████████████████████████████████████ | -- 147520 ████████████████████████████████████████ | -- 147608 ████████████████████████████████████████ | -- 147752 ████████████████████████████████████████ | -- 147748 ████████████████████████████████████████ | -- 147796 ████████████████████████████████████████▏ | -- 147756 ████████████████████████████████████████ | hs/space-bs-c8-foldrx: 147448 ████████████████████████████████████████ | -- 147496 ████████████████████████████████████████ | -- 147608 ████████████████████████████████████████ | -- 147732 ████████████████████████████████████████ | -- 147748 ████████████████████████████████████████ | -- 147760 ████████████████████████████████████████ | -- 147756 ████████████████████████████████████████ | hs/space-bs-c8-lenfil: 147464 ████████████████████████████████████████ | -- 147524 ████████████████████████████████████████ | -- 167176 █████████████████████████████████████████████▍| -- 147756 ████████████████████████████████████████ | -- 167300 █████████████████████████████████████████████▍| -- 147788 ████████████████████████████████████████ | -- 167320 █████████████████████████████████████████████▍| hs/space-bslc8-acc-1: 2872 ▊ | -- 2920 ▊ | -- 3048 ▉ | -- 3192 ▉ | -- 3228 ▉ | -- 3180 ▉ | -- 3196 ▉ | hs/space-bslc8-acc-2: 2872 ▊ | -- 2924 ▊ | -- 3048 ▉ | -- 3192 ▉ | -- 3228 ▉ | -- 3180 ▉ | -- 3200 ▉ | hs/space-bslc8-acc-3: 2868 ▊ | -- 2924 ▊ | -- 3052 ▉ | -- 3196 ▉ | -- 3232 ▉ | -- 3172 ▉ | -- 3208 ▉ | hs/space-bslc8-count: 1476 ▍ | -- 1520 ▍ | -- 1656 ▌ | -- 79204 █████████████████████▌ | -- 82248 ██████████████████████▎ | -- 79220 █████████████████████▌ | -- 82224 ██████████████████████▎ | hs/space-bslc8-foldl: 1552 ▍ | -- 1620 ▌ | -- 1632 ▌ | -- 85868 ███████████████████████▎ | -- 79224 █████████████████████▌ | -- 85852 ███████████████████████▎ | -- 79196 █████████████████████▌ | hs/space-bslc8-foldlx-1: 1556 ▍ | -- 1620 ▌ | -- 1636 ▌ | -- 85864 ███████████████████████▎ | -- 79224 █████████████████████▌ | -- 85852 ███████████████████████▎ | -- 79196 █████████████████████▌ | hs/space-bslc8-foldlx-2: 1552 ▍ | -- 1616 ▌ | -- 1636 ▌ | -- 85868 ███████████████████████▎ | -- 79224 █████████████████████▌ | -- 85852 ███████████████████████▎ | -- 79196 █████████████████████▌ | hs/space-bslc8-foldr-1: 169480 ██████████████████████████████████████████████| -- 169544 ██████████████████████████████████████████████| -- 149076 ████████████████████████████████████████▍ | -- 169700 ██████████████████████████████████████████████| -- 149704 ████████████████████████████████████████▋ | -- 169680 ██████████████████████████████████████████████| -- 149680 ████████████████████████████████████████▋ | hs/space-bslc8-foldr-2: 169480 ██████████████████████████████████████████████| -- 169544 ██████████████████████████████████████████████| -- 149076 ████████████████████████████████████████▍ | -- 169700 ██████████████████████████████████████████████| -- 149708 ████████████████████████████████████████▋ | -- 169676 ██████████████████████████████████████████████| -- 149676 ████████████████████████████████████████▋ | hs/space-bslc8-lenfil-1: 38632 ██████████▌ | -- 38644 ██████████▌ | -- 1940 ▌ | -- 109404 █████████████████████████████▋ | -- 82324 ██████████████████████▍ | -- 109388 █████████████████████████████▋ | -- 82304 ██████████████████████▎ | hs/space-bslc8-lenfil-2: 38628 ██████████▌ | -- 38648 ██████████▌ | -- 1940 ▌ | -- 109404 █████████████████████████████▋ | -- 82328 ██████████████████████▍ | -- 109392 █████████████████████████████▋ | -- 82300 ██████████████████████▎ | hs/space-bsl---foldlx: 1560 ▍ | -- 1616 ▌ | -- 1620 ▌ | -- 85836 ███████████████████████▎ | -- 79184 █████████████████████▌ | -- 85864 ███████████████████████▎ | -- 79208 █████████████████████▌ | hs/space-xxxxx-acc-1: 1568 ▍ | -- 1636 ▌ | -- 1636 ▌ | -- 1904 ▌ | -- 1904 ▌ | -- 1900 ▌ | -- 1904 ▌ | hs/space-xxxxx-acc-2: 1572 ▍ | -- 1636 ▌ | -- 1636 ▌ | -- 1904 ▌ | -- 1900 ▌ | -- 1904 ▌ | -- 1900 ▌ | hs/space-xxxxx-foldl: 1572 ▍ | -- 1636 ▌ | -- 1636 ▌ | -- 1900 ▌ | -- 1904 ▌ | -- 1904 ▌ | -- 1904 ▌ | hs/space-xxxxx-lenfil: 1556 ▍ | -- 1608 ▍ | -- 1604 ▍ | -- 1892 ▌ | -- 1892 ▌ | -- 1888 ▌ | -- 1888 ▌ | hs/space-bslc8-chunk-1: n/a -- 1512 ▍ | -- 1636 ▌ | -- 65192 █████████████████▋ | -- 66216 ██████████████████ | -- 65204 █████████████████▋ | -- 66224 ██████████████████ | hs/space-bslc8-chunk-2: n/a -- 1512 ▍ | -- 1640 ▌ | -- 65192 █████████████████▋ | -- 66216 ██████████████████ | -- 65204 █████████████████▋ | -- 66228 ██████████████████ | hs/space-bslc8-chunk-3: n/a -- 1548 ▍ | -- 1644 ▌ | -- 75240 ████████████████████▍ | -- 66208 ██████████████████ | -- 75216 ████████████████████▍ | -- 66224 ██████████████████ | hs/space-bslc8-chunk-4: n/a -- 1512 ▍ | -- 1636 ▌ | -- 76188 ████████████████████▋ | -- 79232 █████████████████████▌ | -- 76176 ████████████████████▋ | -- 79204 █████████████████████▌ |

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Class/Instance : what am I doing wrong in this example ?
by david48 20 Dec '07

20 Dec '07

I'm really inexperienced at this : ----------- {-# OPTIONS_GHC -fglasgow-exts -funbox-strict-fields -fallow-undecidable-instances -O2 #-} class Gadget g where fInit :: g -> a -> g data FString = FString !Int !String deriving Show instance Gadget FString where fInit (FString n _) s = FString n (take n s) ------------- I get the error message : Couldn't match expected type `String' against inferred type `a' `a' is a rigid type variable bound by the type signature for `fInit' at Gadget.hs:4:17 In the second argument of `FString', namely `s' In the expression: FString n s In the definition of `fInit': fInit (FString n _) s = FString n s

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