Re: [Haskell-cafe] need help with understanding expression
Yes, same problem, and again I have no idea how to read the type Prelude :t max. 3 2 max. 3 2 :: (Ord b, Num a1, Num (a1 - a - b)) = a - b - b What does the type mean in plain english? Daryoush On Thu, Nov 15, 2012 at 11:56 PM, Ramana Kumar ramana.ku...@cl.cam.ac.ukwrote: Another experiment may be revealing: :t 3 2 On Fri, Nov 16, 2012 at 7:46 AM, Daryoush Mehrtash dmehrt...@gmail.comwrote: I see the point with :t (.) that max.(+1) 2 2 is the same as max. 3 2 Which is not what I want. But I have no idea what the type signature of this expression mean now Prelude :t max. 3 2 max. 3 2 :: (Ord b, Num a1, Num (a1 - a - b)) = a - b - b Any idea? Daryoush On Thu, Nov 15, 2012 at 11:19 PM, Ramana Kumar ramana.ku...@cl.cam.ac.uk wrote: Hi Daryoush, I recommend you try these experiments first, and then reply back if you're still confused. :t max :t (+1) :t max . (+1) :t (+1) 2 :t (.) On Fri, Nov 16, 2012 at 7:10 AM, Daryoush Mehrtash dmehrt...@gmail.comwrote: I am having hard time understanding how removing the outer parenthesis in (max.(+1)) 2 2 to max.(+1) 2 2 changes the meaning of expression. My expectation was that max.(+1) takes two numbers and returns the max as defined in the type: :t max.(+1) max.(+1) :: (Ord b, Num b) = b - b - b With parenthesis it does what I expect it to: Prelude :t (max.(+1)) 2 2 (max.(+1)) 2 2 :: (Ord b, Num b) = b Prelude (max.(+1)) 2 2 3 But if I remove the parenthesis I get a beast that I have no idea what its type signature mean any more Prelude :t (max.(+1)) 2 2 (max.(+1)) 2 2 :: (Ord b, Num b) = b Prelude :t max.(+1) 2 2 max.(+1) 2 2 :: (Ord b, Num a1, Num (a1 - a - b)) = a - b - b How did removal of parenthesis changed the meaning? How do you interpret the type: (Ord b, Num a1, Num (a1 - a - b)) = a - b - b? Thanks -- Daryoush Weblog: http://onfp.blogspot.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Daryoush Weblog: http://onfp.blogspot.com/ -- Daryoush Weblog: http://onfp.blogspot.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] need help with understanding expression
Sorry wrong paste Prelude :t 3 2 3 2 :: (Num a, Num (a - t)) = t What does the type mean in plain english? Daryoush On Fri, Nov 16, 2012 at 12:00 AM, Daryoush Mehrtash dmehrt...@gmail.comwrote: Yes, same problem, and again I have no idea how to read the type Prelude :t max. 3 2 max. 3 2 :: (Ord b, Num a1, Num (a1 - a - b)) = a - b - b What does the type mean in plain english? Daryoush On Thu, Nov 15, 2012 at 11:56 PM, Ramana Kumar ramana.ku...@cl.cam.ac.ukwrote: Another experiment may be revealing: :t 3 2 On Fri, Nov 16, 2012 at 7:46 AM, Daryoush Mehrtash dmehrt...@gmail.comwrote: I see the point with :t (.) that max.(+1) 2 2 is the same as max. 3 2 Which is not what I want. But I have no idea what the type signature of this expression mean now Prelude :t max. 3 2 max. 3 2 :: (Ord b, Num a1, Num (a1 - a - b)) = a - b - b Any idea? Daryoush On Thu, Nov 15, 2012 at 11:19 PM, Ramana Kumar ramana.ku...@cl.cam.ac.uk wrote: Hi Daryoush, I recommend you try these experiments first, and then reply back if you're still confused. :t max :t (+1) :t max . (+1) :t (+1) 2 :t (.) On Fri, Nov 16, 2012 at 7:10 AM, Daryoush Mehrtash dmehrt...@gmail.com wrote: I am having hard time understanding how removing the outer parenthesis in (max.(+1)) 2 2 to max.(+1) 2 2 changes the meaning of expression. My expectation was that max.(+1) takes two numbers and returns the max as defined in the type: :t max.(+1) max.(+1) :: (Ord b, Num b) = b - b - b With parenthesis it does what I expect it to: Prelude :t (max.(+1)) 2 2 (max.(+1)) 2 2 :: (Ord b, Num b) = b Prelude (max.(+1)) 2 2 3 But if I remove the parenthesis I get a beast that I have no idea what its type signature mean any more Prelude :t (max.(+1)) 2 2 (max.(+1)) 2 2 :: (Ord b, Num b) = b Prelude :t max.(+1) 2 2 max.(+1) 2 2 :: (Ord b, Num a1, Num (a1 - a - b)) = a - b - b How did removal of parenthesis changed the meaning? How do you interpret the type: (Ord b, Num a1, Num (a1 - a - b)) = a - b - b? Thanks -- Daryoush Weblog: http://onfp.blogspot.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Daryoush Weblog: http://onfp.blogspot.com/ -- Daryoush Weblog: http://onfp.blogspot.com/ -- Daryoush Weblog: http://onfp.blogspot.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] need help with understanding expression
On Fri, Nov 16, 2012 at 8:00 AM, Daryoush Mehrtash dmehrt...@gmail.comwrote: Sorry wrong paste Prelude :t 3 2 3 2 :: (Num a, Num (a - t)) = t It means that 2 has type a (which must be in the Num class), 3 has type (a - t) (which also must be in the Num class), and the type of (3 2) is therefore t. When you apply one expression to another, the first must have function type, and the second must have the type of the domain of the function, hence the a - t and a. Furthermore, the numeric literals are always interpreted as being in the Num class. I haven't been able to find any good introduction to numeric literals and the Num class with quick search, so if anyone else on list can point us to one (if it exists) that would be great. What does the type mean in plain english? Daryoush On Fri, Nov 16, 2012 at 12:00 AM, Daryoush Mehrtash dmehrt...@gmail.comwrote: Yes, same problem, and again I have no idea how to read the type Prelude :t max. 3 2 max. 3 2 :: (Ord b, Num a1, Num (a1 - a - b)) = a - b - b What does the type mean in plain english? Daryoush On Thu, Nov 15, 2012 at 11:56 PM, Ramana Kumar ramana.ku...@cl.cam.ac.uk wrote: Another experiment may be revealing: :t 3 2 On Fri, Nov 16, 2012 at 7:46 AM, Daryoush Mehrtash dmehrt...@gmail.comwrote: I see the point with :t (.) that max.(+1) 2 2 is the same as max. 3 2 Which is not what I want. But I have no idea what the type signature of this expression mean now Prelude :t max. 3 2 max. 3 2 :: (Ord b, Num a1, Num (a1 - a - b)) = a - b - b Any idea? Daryoush On Thu, Nov 15, 2012 at 11:19 PM, Ramana Kumar ramana.ku...@cl.cam.ac.uk wrote: Hi Daryoush, I recommend you try these experiments first, and then reply back if you're still confused. :t max :t (+1) :t max . (+1) :t (+1) 2 :t (.) On Fri, Nov 16, 2012 at 7:10 AM, Daryoush Mehrtash dmehrt...@gmail.com wrote: I am having hard time understanding how removing the outer parenthesis in (max.(+1)) 2 2 to max.(+1) 2 2 changes the meaning of expression. My expectation was that max.(+1) takes two numbers and returns the max as defined in the type: :t max.(+1) max.(+1) :: (Ord b, Num b) = b - b - b With parenthesis it does what I expect it to: Prelude :t (max.(+1)) 2 2 (max.(+1)) 2 2 :: (Ord b, Num b) = b Prelude (max.(+1)) 2 2 3 But if I remove the parenthesis I get a beast that I have no idea what its type signature mean any more Prelude :t (max.(+1)) 2 2 (max.(+1)) 2 2 :: (Ord b, Num b) = b Prelude :t max.(+1) 2 2 max.(+1) 2 2 :: (Ord b, Num a1, Num (a1 - a - b)) = a - b - b How did removal of parenthesis changed the meaning? How do you interpret the type: (Ord b, Num a1, Num (a1 - a - b)) = a - b - b? Thanks -- Daryoush Weblog: http://onfp.blogspot.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Daryoush Weblog: http://onfp.blogspot.com/ -- Daryoush Weblog: http://onfp.blogspot.com/ -- Daryoush Weblog: http://onfp.blogspot.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] need help with understanding expression
Hi Daryoush, Prelude :t 3 2 3 2 :: (Num a, Num (a - t)) = t What does the type mean in plain english? It's important to remember that numeric literals are polymorphic. That is, 3 :: Num a = a. They do not have monomorphic types such as Int or Integer. In the above, GHCi is inferring the principal type of 3 applied to 2. Since 3 is in the position of function application, it should have a function type, e.g. a - t. And 2 is the argument to 3, so it has the type 'a'. But there must be Num constraints on these types, and that's what the context (Num a, Num (a - t)) is telling you. Num (a - t) is a strange constraint but so is applying 3 to 2. Whenever you see a Num constraint on a function type, it probably means you're doing something wrong. You might find the (brief) description of typing numeric literals in the language definition helpful: http://www.haskell.org/onlinereport/haskell2010/haskellch6.html#x13-1360006.4.1 Also, in response to your initial query... I am having hard time understanding how removing the outer parenthesis in (max.(+1)) 2 2 to max.(+1) 2 2 Keep in mind the precedence of the function composition operator (.) here: Prelude :i (.) (.) :: (b - c) - (a - b) - a - c -- Defined in GHC.Base infixr 9 . Function application is infixl 10, so even though max . (+1) :: (Num b, Ord b) = b - b - b, when you do max . (+1) 2, the application of (+1) to 2 binds more tightly than (.). A common idiom for removing parentheses with a sequence of compositions is to use ($): Prelude :i ($) ($) :: (a - b) - a - b -- Defined in GHC.Base infixr 0 $ Note that it has the lowest possible precedence. So, you often see the composition of functions as f . g . h $ arg. But this doesn't work well for (curried) functions with 2 arguments. So, in your case, I'd guess the parentheses is simplest idiomatic solution. Though, I think I'd prefer max (succ 2) 2. Regards, Sean ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I killed performance of my code with Eval and Strategies
Just another definition of calculateSeq:
calculateSeq = zipWith ($) (cycle [sin,cos]) . map sqrt
2012/11/15 Janek S. fremenz...@poczta.onet.pl
Do you really mean to calculate the 'sin . sqrt' of just the head of the
list, or do you mean:
calculateSeq = map (sin . sqrt) ?
Argh.. of course not! That's what you get when you code in the middle of a
night. But in my code I
will not be able to use map because elements will be processed in pairs,
so let's say that my
sequential function looks like this:
calculateSeq :: [Double] - [Double]
calculateSeq [] = []
calculateSeq [x] = [sin . sqrt $ x]
calculateSeq (x:y:xs) = (sin . sqrt $ x) : (cos . sqrt $ y) : calculateSeq
xs
I don't think there's a memory leak. It looks more like you're just
allocating much more than is sane for such a simple function.
On a recent processor, sin . sqrt is two instructions. Meanwhile, you
have
a list of (boxed?) integers being split up, then recombined. That's bound
to hurt the GC.
I am not entirely convinced that my idea of using eval+strategies is bound
to be slow, because
there are functions like parListChunk that do exactly this: split the list
into chunks, process
them in parallel and then concatenate the result. Functions in
Control.Parallel.Strategies were
designed to deal with list so I assume it is possible to process lists in
parallel without GC
problems. However I do not see a way to apply these functions in my
setting where elements of
lists are processed in pairs, not one at a time (parList and parMap will
not do). Also, working
on a list of tuples will not do.
Also, you might want to configure criterion to GC between
runs. That might help.
The -g flag passed to criterion executable does that.
What I'd suggest doing instead, is breaking the input into chucks of,
say,
1024, and representing it with a [Vector]. Then, run your sin.sqrt's on
each vector in parallel. Finally, use Data.Vector.concat to combine your
result.
As stated in my post scriptum I am aware of that solution :) Here I'm
trying to figure what am I
doing wrong with Eval.
Thanks!
Janek
Hope that helps,
- Clark
On Wed, Nov 14, 2012 at 4:43 PM, Janek S. fremenz...@poczta.onet.pl
wrote:
Dear Haskellers,
I am reading Simon Marlow's tutorial on parallelism and I have problems
with correctly using Eval
monad and Strategies. I *thought* I understand them but after writing
some code it turns out that
obviously I don't because parallelized code is about 20 times slower.
Here's a short example
(code + criterion benchmarks):
{-# LANGUAGE BangPatterns #-}
module Main where
import Control.Parallel.Strategies
import Criterion.Main
main :: IO ()
main = defaultMain [
bench Seq $ nf calculateSeq xs
, bench Par $ nf calculatePar xs ]
where xs = [1..16384]
calculateSeq :: [Double] - [Double]
calculateSeq [] = []
calculateSeq (x:xs) = (sin . sqrt $ x) : xs
calculatePar :: [Double] - [Double]
calculatePar xss = runEval $ go xss
where
go :: Strategy [Double]
go [] = return []
go xs = do
lsh - (rpar `dot` rdeepseq) $ calculateSeq as
lst - go bs
return (lsh ++ lst)
where
!(as, bs) = splitAt 8192 xs
Compiling and running with:
ghc -O2 -Wall -threaded -rtsopts -fforce-recomp -eventlog evalleak.hs
./evalleak -oreport.html -g +RTS -N2 -ls -s
I get:
benchmarking Seq
mean: 100.5990 us, lb 100.1937 us, ub 101.1521 us, ci 0.950
std dev: 2.395003 us, lb 1.860923 us, ub 3.169562 us, ci 0.950
benchmarking Par
mean: 2.233127 ms, lb 2.169669 ms, ub 2.296155 ms, ci 0.950
std dev: 323.5201 us, lb 310.2844 us, ub 344.8252 us, ci 0.950
That's a hopeless result. Looking at the spark allocation everything
looks fine:
SPARKS: 202 (202 converted, 0 overflowed, 0 dud, 0 GC'd, 0 fizzled)
But analyzing eventlog with ThreadScope I see that parallel function
spends most of the time doing
garbage collection, which suggests that I have a memory leak
somewhere. I
suspected that problem
might be caused by appending two lists together in the parallel
implementation, but replacing
this with difference lists doesn't help. Changing granularity (e.g.
splitAt 512) also brings no
improvement. Can anyone point me to what am I doing wrong?
Janek
PS. This is of course not a real world code - I know that I'd be better
of using unboxed data
structures for doing computations on Doubles.
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Re: [Haskell-cafe] How to determine correct dependency versions for a library?
Aleksey Khudyakov alexey.sklad...@gmail.com writes: Adding more restrictive constraints does not work, the broken package will be on hackage forever, while adding a new version with relaxed constraints works well. That illustrate real problem It's not possible to specify correct version constraints when package is uploaded. So one have to choose between optimistic and conservative approach. Both have disadvantages. In ideal world one need ability to adjust version bounds after package upload. +1. Metadata (i.e. the cabal file) chould be editable. In addition to adjusting dependency bounds, Hackage (or third party build servers) could add Tested-With, and there could be a deprecated field added when problems are discovered. -k ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to determine correct dependency versions for a library?
Hi Tobias, A 1.1.4.0 build-depends: B ==2.5.* C ==3.7.* (overspecified) B 2.5.3.0 build-depends: C ==3.* (underspecified) C 3.7.1.0 Everything works nice until C-3.8.0.0 appears with incompatible changes that break B, but not A. Now both A and B have to update their dependencies and we have now: A 1.1.5.0 build-depends: B ==2.5.* C =3.7 3.9 B 2.5.4.0 build-depends: C =3 3.8 C 3.8.0.0 And now the following combination is still valid: A 1.1.5.0 B 2.5.3.0 (old version) C 3.8.0.0 Bang! thank you for contributing this insightful example. When such a situation has arisen in the past, it's my experience that the author of B typically releases an update to fix the issue with the latest version of C: B 2.5.4.0 build-depends: C = 3.8 So that particular conflict does hardly ever occur in practice. Note that package A would build just fine after that update of B -- if the author of A hadn't overspecified its dependencies. As it is, however, a new version of A has to released that changes no code, but only the Cabal file. Take care, Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Taking over ghc-core
how would ghc-core enable targetting core for Agda? On Wed, Nov 14, 2012 at 6:32 PM, Andreas Abel andreas.a...@ifi.lmu.dewrote: Excellent! With ghc-core being maintained again, we can start thinking about compiling Agda to core instead of hs. Andreas On 11.11.12 11:41 AM, Bas van Dijk wrote: Great! On 10 November 2012 16:17, Shachaf Ben-Kiki shac...@gmail.com wrote: With Don Stewart's blessing (https://twitter.com/donsbot/**status/267060717843279872https://twitter.com/donsbot/status/267060717843279872), I'll be taking over maintainership of ghc-core, which hasn't been updated since 2010. I'll release a version with support for GHC 7.6 later today. Shachaf __**_ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/**mailman/listinfo/haskell-cafehttp://www.haskell.org/mailman/listinfo/haskell-cafe -- Andreas AbelDu bist der geliebte Mensch. Theoretical Computer Science, University of Munich Oettingenstr. 67, D-80538 Munich, GERMANY andreas.a...@ifi.lmu.de http://www2.tcs.ifi.lmu.de/~**abel/ http://www2.tcs.ifi.lmu.de/~abel/ __**_ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/**mailman/listinfo/haskell-cafehttp://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to determine correct dependency versions for a library?
Peter Simons sim...@cryp.to wrote: Hi Tobias, A 1.1.4.0 build-depends: B ==2.5.* C ==3.7.* (overspecified) B 2.5.3.0 build-depends: C ==3.* (underspecified) C 3.7.1.0 Everything works nice until C-3.8.0.0 appears with incompatible changes that break B, but not A. Now both A and B have to update their dependencies and we have now: A 1.1.5.0 build-depends: B ==2.5.* C =3.7 3.9 B 2.5.4.0 build-depends: C =3 3.8 C 3.8.0.0 And now the following combination is still valid: A 1.1.5.0 B 2.5.3.0 (old version) C 3.8.0.0 Bang! thank you for contributing this insightful example. When such a situation has arisen in the past, it's my experience that the author of B typically releases an update to fix the issue with the latest version of C: B 2.5.4.0 build-depends: C = 3.8 So that particular conflict does hardly ever occur in practice. And what if the maintainer of a takes the chance to make some major updates and directly releases 2.6? Then all packages depending on 2.5.* will probably break. Note that package A would build just fine after that update of B -- if the author of A hadn't overspecified its dependencies. As it is, however, a new version of A has to released that changes no code, but only the Cabal file. But all this boils down to a system where only a combination of latest versions will be stable. So why restrict dependencies anyway? Tobi ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to determine correct dependency versions for a library?
Ketil Malde ke...@malde.org wrote: Aleksey Khudyakov alexey.sklad...@gmail.com writes: Adding more restrictive constraints does not work, the broken package will be on hackage forever, while adding a new version with relaxed constraints works well. That illustrate real problem It's not possible to specify correct version constraints when package is uploaded. So one have to choose between optimistic and conservative approach. Both have disadvantages. In ideal world one need ability to adjust version bounds after package upload. +1. Metadata (i.e. the cabal file) chould be editable. In addition to adjusting dependency bounds, Hackage (or third party build servers) could add Tested-With, and there could be a deprecated field added when problems are discovered. The last version component (D in A.B.C.D) could be considered the metadata version. Then cabal could be changed to only take into account the highest D-values. Alternatively, if the semantics of D cannot be changed, make it A.B.C.D_M (M for metadata version). That's the way MacPorts handles the problem. Tobi ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] need help with understanding expression
On 12-11-16 02:10 AM, Daryoush Mehrtash wrote:
I am having hard time understanding how removing the outer parenthesis in
(max.(+1)) 2 2
to
max.(+1) 2 2
changes the meaning of expression.
I recommend http://bm380.user.srcf.net/prettyparsetree.cgi for
discovering the correct parse.
Specifically,
max.(+1) 2 2
= { use uniform spacing to un-presume }
max . (+1) 2 2
= { . is lower than application }
max . ((+1) 2 2)
etc.
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Re: [Haskell-cafe] Taking over ghc-core
On Fri, 16 Nov 2012, Carter Schonwald carter.schonw...@gmail.com wrote: how would ghc-core enable targetting core for Agda? On Wed, Nov 14, 2012 at 6:32 PM, Andreas Abel andreas.a...@ifi.lmu.dewrote: Excellent! With ghc-core being maintained again, we can start thinking about compiling Agda to core instead of hs. Andreas I would like to be able to take the textual version of Core output by GHC and use that text as input to the next stage of compilation. oo--JS. On 11.11.12 11:41 AM, Bas van Dijk wrote: Great! On 10 November 2012 16:17, Shachaf Ben-Kiki shac...@gmail.com wrote: With Don Stewart's blessing (https://twitter.com/donsbot/**status/267060717843279872https://twitter.com/donsbot/status/267060717843279872), I'll be taking over maintainership of ghc-core, which hasn't been updated since 2010. I'll release a version with support for GHC 7.6 later today. Shachaf __**_ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/**mailman/listinfo/haskell-cafehttp://www.haskell.org/mailman/listinfo/haskell-cafe -- Andreas AbelDu bist der geliebte Mensch. Theoretical Computer Science, University of Munich Oettingenstr. 67, D-80538 Munich, GERMANY andreas.a...@ifi.lmu.de http://www2.tcs.ifi.lmu.de/~**abel/ http://www2.tcs.ifi.lmu.de/~abel/ __**_ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/**mailman/listinfo/haskell-cafehttp://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Taking over ghc-core
On Fri, Nov 16, 2012 at 03:25:35PM -0500, Jay Sulzberger wrote: On Fri, 16 Nov 2012, Carter Schonwald carter.schonw...@gmail.com wrote: how would ghc-core enable targetting core for Agda? On Wed, Nov 14, 2012 at 6:32 PM, Andreas Abel andreas.a...@ifi.lmu.dewrote: Excellent! With ghc-core being maintained again, we can start thinking about compiling Agda to core instead of hs. Andreas I would like to be able to take the textual version of Core output by GHC and use that text as input to the next stage of compilation. oo--JS. Note that the ghc-core package only does pretty-printing of GHC core. Whether GHC can parse a textual representation of GHC core (like Jay and, presumably, Andreas want) is unrelated to the ghc-core package. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Taking over ghc-core
On Fri, 16 Nov 2012, Brent Yorgey byor...@seas.upenn.edu wrote: On Fri, Nov 16, 2012 at 03:25:35PM -0500, Jay Sulzberger wrote: On Fri, 16 Nov 2012, Carter Schonwald carter.schonw...@gmail.com wrote: how would ghc-core enable targetting core for Agda? On Wed, Nov 14, 2012 at 6:32 PM, Andreas Abel andreas.a...@ifi.lmu.dewrote: Excellent! With ghc-core being maintained again, we can start thinking about compiling Agda to core instead of hs. Andreas I would like to be able to take the textual version of Core output by GHC and use that text as input to the next stage of compilation. oo--JS. Note that the ghc-core package only does pretty-printing of GHC core. Whether GHC can parse a textual representation of GHC core (like Jay and, presumably, Andreas want) is unrelated to the ghc-core package. -Brent Thanks, Brent! My post was based on ignorance. OK, I would like to suggest a talk at NYHUG on the GHC pipeline. Else I might look at it without the support of NYHUGgers and drink. oo--JS. ___ 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
Re: [Haskell-cafe] How to determine correct dependency versions for a library?
Hi Tobias, When such a situation has arisen in the past, it's my experience that the author of B typically releases an update to fix the issue with the latest version of C: B 2.5.4.0 build-depends: C = 3.8 So that particular conflict does hardly ever occur in practice. And what if the maintainer of a takes the chance to make some major updates and directly releases 2.6? Then all packages depending on 2.5.* will probably break. yes, that is true. In such a case, one would have to contact the maintainer of A, B, and C to discuss how to remedy the issue. Fortunately, pathological cases such as this one seem to happen rarely in practice. All this boils down to a system where only a combination of latest versions will be stable. So why restrict dependencies anyway? Now, I think that is an exaggeration. Do you know a single example of a package on Hackage that actually suffers from the problem you're describing? Take care, Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Polymorphic Type Safe URL building -- I need advice on my project
Hello, So I started working on a project involving polymorphic type safe urls. I know there are other type-safe url's out there, but I want some advice before I start reorganizing it. It is located here: https://github.com/dracule/web-scatter One might ask why you would want polymorphic types in your URL. Current implementation of type-safe URLs use a single type and then have it pattern match on the constructors. However, It is a pretty common occurrence that you might want to use a type from other parts of code. Where this becomes prevalent is in IxSet and AcidState. For IxSet your Index keys all have to have separate types . So with this, you can convert your url into your index key's type and then just make your handler like this: myHandler :: BlogId - SomeWebHandler I know my code probably has some terrible inefficiencies or something, so I am looking for some feedback on some jarring problems. Thank You ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: hledger-web 0.19
I'm pleased to announce hledger-web 0.19, compatible with the latest hledger and Yesod. Release notes: * web: builds with yesod 1.1.3 * web: obeys command-line query options at startup again * the autogenerated session file is now a dot file (.hledger-web_client_session.aes) hledger is a command-line tool and haskell library for tracking financial transactions, which are stored in a human-readable plain text format. In addition to reporting, it can also help you record new transactions, or convert CSV data from your bank. Add-on packages include hledger-web, a web interface. hledger is inspired by and compatible with John Wiegley's Ledger. For more, see http://hledger.org . Install it: cabal update; cabal install hledger-web For more installation help, see http://hledger.org/MANUAL.html#installing . Or, sponsor a ready-to-run binary for your platform: http://hledger.org/DOWNLOAD.html . ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] need help with understanding expression
Let's see tthis: Prelude :t 3 a 3 a :: (Num ([Char] - t)) = t No complaint from GHC; but now see this: Prelude :t a 3 interactive:1:0: Couldn't match expected type `t1 - t' against inferred type `[Char]' In the expression: a 3 Why does it not fail for (:t 3 a) but does fail for (:t a 3)? In the second case, why the GHC doesn't give something like? ([Char] (a - t), Num a) = t In other words, how the first one does make sense (however strange the sense may seem) to GHC while the second one doesn't? Now let's consider the evaluation scenario: Prelude 3 2 interactive:1:0: No instance for (Num (t - t1)) arising from the literal `3' at interactive:1:0-2 Possible fix: add an instance declaration for (Num (t - t1)) In the expression: 3 2 In the definition of `it': it = 3 2 Note, how the GHC suggests us this strange constraint as a *possible fix*BUT see this: Prelude a 2 interactive:1:0: Couldn't match expected type `t1 - t' against inferred type `[Char]' In the expression: a 2 In the definition of `it': it = a 2 In this case the GHC doesn't even allow us to add any possible fix. -Damodar On Fri, Nov 16, 2012 at 2:27 PM, Sean Leather leat...@cs.uu.nl wrote: Hi Daryoush, Prelude :t 3 2 3 2 :: (Num a, Num (a - t)) = t What does the type mean in plain english? It's important to remember that numeric literals are polymorphic. That is, 3 :: Num a = a. They do not have monomorphic types such as Int or Integer. In the above, GHCi is inferring the principal type of 3 applied to 2. Since 3 is in the position of function application, it should have a function type, e.g. a - t. And 2 is the argument to 3, so it has the type 'a'. But there must be Num constraints on these types, and that's what the context (Num a, Num (a - t)) is telling you. Num (a - t) is a strange constraint but so is applying 3 to 2. Whenever you see a Num constraint on a function type, it probably means you're doing something wrong. You might find the (brief) description of typing numeric literals in the language definition helpful: http://www.haskell.org/onlinereport/haskell2010/haskellch6.html#x13-1360006.4.1 Also, in response to your initial query... I am having hard time understanding how removing the outer parenthesis in (max.(+1)) 2 2 to max.(+1) 2 2 Keep in mind the precedence of the function composition operator (.) here: Prelude :i (.) (.) :: (b - c) - (a - b) - a - c -- Defined in GHC.Base infixr 9 . Function application is infixl 10, so even though max . (+1) :: (Num b, Ord b) = b - b - b, when you do max . (+1) 2, the application of (+1) to 2 binds more tightly than (.). A common idiom for removing parentheses with a sequence of compositions is to use ($): Prelude :i ($) ($) :: (a - b) - a - b -- Defined in GHC.Base infixr 0 $ Note that it has the lowest possible precedence. So, you often see the composition of functions as f . g . h $ arg. But this doesn't work well for (curried) functions with 2 arguments. So, in your case, I'd guess the parentheses is simplest idiomatic solution. Though, I think I'd prefer max (succ 2) 2. Regards, Sean ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Thanks and regards, -Damodar Kulkarni ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
