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Re: Haskell type system (Peter Verswyvelen) ---------------------------------------------------------------------- Message: 1 Date: Mon, 21 Sep 2009 18:38:48 -0400 From: Joe Fredette <jfred...@gmail.com> Subject: Re: [Haskell-beginners] edit-compile-test loop To: Tom Doris <tomdo...@gmail.com> Cc: Haskell Beginners <beginners@haskell.org> Message-ID: <db877768-ad1f-4ecd-b155-7d9aa9a73...@gmail.com> Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes Well, basically I switch from doing manual "testing" (entering functions with test arguments by hand into ghci, checking types w/ the inferrer, etc.) to compiling via cabal build (which requires me to make sure I've got all the appropriate modules listed in the appropriate places, make sure I'm not importing hidden modules, etc) and running a test suite (typically QuickCheck properties with some HUnit thrown in around the IO stuff and for corner cases of functions (eg, making sure things fail gracefully when I have to write a partial function, etc)) and working generally more as if I were writing in a language like Java (where most of my dev cycle is interacting with JUnit, rather than a interpreter). Typically it works out to: 1> edit some stuff 2> cabal build 3> fix any errors; goto 1 else continue 4> run test suite [see 1] 5> if any tests fail, and that wasn't expected, fix the issue; goto 1 else continue 6> goto 1 until ready for release. Towards the release date, this process helps me add functionality slower, and ensure everything is actually doing what it's supposed to. I tend to work on projects solo, so I'll do various naughty things like develop without writing alot of tests or documenting, etc. When I get ready to release, I really want to make sure I've covered everything that needs to be tested with tests, documented everything appropriately. As I code (even before this part of the project) I generally keep track of what I should write tests for, even if I haven't written the test yet. During this phase I build up the test suite to cover all the things I've written down, and the test suite kind of becomes part of the specification at that point. If something in the future causes an early test to fail, then that change "breaks" the program, if it causes a current test to fail, then I might want to see if that test is really ensuring the property I want. I should note, I'm not a CS-guy, I'm a math guy, and this kind of methodology is more like when I write a math paper than what I think most people do when they code. When I have a ECT loop for math papers, it starts with me making wild conjectures and "testing" them (trying to come up with proof sketches), later that turns to this slower process of actually, formally proving things (the compiling part of this cycle) and finally it hits the, "Now make it pretty" phase, where I eliminate superfluous arguments/lemmas, rework proofs to flow better, etc (the "make sure the tests pass" phase). I don't know if this is similar to "normal" dev cycles, but it does me nicely. :) HTH /Joe [1] right now I use my own little hacked up testrunning script (just loads the stuff in ghci, and I have one function that sits in a base "test" directory, underwhich the project module hierarchy is mirrored. So if I have, as I do now, Text/HWN/Parser/HWN.hs, then I also have Test/Text/HWN/Parser/HWN_Test.hs. in the Test directory I have Test_Harness.hs, which has a main function which runs all the tests in the directories below it. Each directory has a similar Test_Harness.hs (though all the names are different) which loads all the tests of the directories below it, and exports a single test group. All of this is manual, though I've been planning a kind of manager thing for it lately. But thats a story for another day. On Sep 21, 2009, at 6:22 PM, Tom Doris wrote: > Thanks, this is very helpful; can you give more detail about your > process once you've transitioned to a "proper test harness/cabal > build", how does this usually hang together? > > > 2009/9/21 Joe Fredette <jfred...@gmail.com> > Assuming I'm starting a brand-new project, it starts by creating a > file in my code directory. initing darcs there, creating the .cabal > file, and creating a basic module hierarchy. After that, I `touch` a > couple of files. add the standard license/description/other header > info... > > When I'm working on the code proper, I have a screen session split > to a ghci session and a vim session editing the file. The ghci sits > in the base directory of the projects (where the _darcs folder is) > and has the files I'm working on loaded. I edit, ^a-tab to ghci, > reload, flip back, fix errors, repeat till it loads. After that, I > run a few tests to make sure the program does what I think it does, > if not, I fix it, then back to adding new functionality. > > I hope this is what you wanted to know. Towards the point where I'm > going to release a version, I substitute the ghci-business to a > proper test harness/cabal build to make sure it compiles all > correctly. > > /Joe > > > On Sep 21, 2009, at 5:35 PM, Tom Doris wrote: > > Hi > I'd like to know what the typical edit-compile-test loop looks like > with the Haskell platform; that is, in C++ this would be edit, run > make to compile everything in the project into libraries and > executables, then run an executable test suite. I'm confused as to > how people work on larger projects in Haskell - do you work on a > single module and load it into ghci to test as you develop, then > compile the entire package and run a test suite? Or do you generally > only use ghci for prototyping and not when in the middle of proper > development? Or do you compile the package and load that into ghci? > I'd like to know as I'm starting to work on patches for some hackage > packages which have proper cabal builds etc., and want to follow the > correct (and efficient!) convention. > Thanks > Tom > > > _______________________________________________ > Beginners mailing list > Beginners@haskell.org > http://www.haskell.org/mailman/listinfo/beginners > > ------------------------------ Message: 2 Date: Wed, 23 Sep 2009 15:03:03 -0700 (PDT) From: "Michael Mossey" <m...@alumni.caltech.edu> Subject: [Haskell-beginners] StateT, list monad To: "Haskell Beginners" <beginners@haskell.org> Message-ID: <3694.75.50.169.210.1253743383.squir...@mail.alumni.caltech.edu> Content-Type: text/plain;charset=iso-8859-1 Trying to understand Douglas Auclair's article "MonadPlus - What a super monad!" here <http://www.haskell.org/sitewiki/images/6/6a/TMR-Issue11.pdf> Defines splits :: Eq a => [a] -> [(a,[a])] splits list = do x <- list return (x, delete x list) choose :: Eq a => StateT [a] [] a choose = StateT (\s -> splits s) I'm trying to understand what "StateT [a] [] a" means: I wrote t1 :: StateT [Int] [] [Int] t1 = do s <- get return s That compiles. Then I tried to write t2 :: StateT [Int] [] [Int] t2 = do x <- [1,2,3] s <- get return (x:s) I thought this would be fine because [1,2,3] is an example of a list monad. But I get "Can't match expected type StateT [Int] [] t against inferred type [a]" ------------------------------ Message: 3 Date: Thu, 24 Sep 2009 00:36:09 +0200 From: Daniel Fischer <daniel.is.fisc...@web.de> Subject: Re: [Haskell-beginners] StateT, list monad To: beginners@haskell.org Message-ID: <200909240036.09934.daniel.is.fisc...@web.de> Content-Type: text/plain; charset="iso-8859-1" Am Donnerstag 24 September 2009 00:03:03 schrieb Michael Mossey: > Trying to understand Douglas Auclair's article > "MonadPlus - What a super monad!" here > <http://www.haskell.org/sitewiki/images/6/6a/TMR-Issue11.pdf> > > Defines > > splits :: Eq a => [a] -> [(a,[a])] > splits list = do x <- list > return (x, delete x list) > > choose :: Eq a => StateT [a] [] a > choose = StateT (\s -> splits s) > > I'm trying to understand what "StateT [a] [] a" means: StateT stateType innerMonad resultType The state is a list of a, the inner monad is the list monad, apart from the newtype wrapper, it's [a] -> [(a,[a])] > > I wrote > > t1 :: StateT [Int] [] [Int] > t1 = do > s <- get > return s > > That compiles. Then I tried to write > > t2 :: StateT [Int] [] [Int] > t2 = do > x <- [1,2,3] > s <- get > return (x:s) > > I thought this would be fine because [1,2,3] is an example of a list monad. Within one do-block, you can use only one monad. do x <- action1 y <- action2 return (f x y) desugars into action1 >>= (\x -> (action2 >>= (\y -> (return (f x y))))) (I used more parentheses than necessary to make the associativity clear, with less clutter, it's action1 >>= \x -> action2 >>= \y -> return (f x y) .) The type of (>>=) is (>>=) :: Monad m => m a -> (a -> m b) -> m b so you can use only one monad in such an expression. With StateT (most monad transformers, I think), you can achieve what you want with t2 :: StateT [Int] [] [Int] t2 = do x <- lift [1,2,3] s <- get return (x:s) 'lift' lifts actions in the inner monad to StateT actions. > > But I get > > "Can't match expected type StateT [Int] [] t > against inferred type [a]" > ------------------------------ Message: 4 Date: Thu, 24 Sep 2009 13:12:01 -0500 From: Hong Yang <hyang...@gmail.com> Subject: [Haskell-beginners] proxy To: beginners@haskell.org Message-ID: <f31db34d0909241112m47873476q33432c6fb0b37...@mail.gmail.com> Content-Type: text/plain; charset="utf-8" Hi, I was using Finance.Quote.Yahoo, but got an error: user error (openTCPConnection: host lookup failure for " download.finance.yahoo.com"). I think it is due to I being behind a proxy. I then imported Network.Browser, ran setProxy, and tried to fetch data using Finance.Quote.Yahoo.getQuote. I still got the error. So I suggest the module author incorporate proxy setting inside the module. Thanks, Hong -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.haskell.org/pipermail/beginners/attachments/20090924/39755102/attachment-0001.html ------------------------------ Message: 5 Date: Sat, 26 Sep 2009 21:29:49 -0700 From: Joe Van Dyk <j...@fixieconsulting.com> Subject: [Haskell-beginners] Distributing executables To: beginners@haskell.org Message-ID: <c715e640909262129v6f0dad28q3a5e13b044ff4...@mail.gmail.com> Content-Type: text/plain; charset=UTF-8 How hard is it to distribute a haskell binary that contains a bunch of libraries embedded in the executable? Is it pretty easy to make a large statically-linked executable? -- Joe Van Dyk http://fixieconsulting.com ------------------------------ Message: 6 Date: Sun, 27 Sep 2009 12:22:50 +0200 From: informationen <informatio...@gmx.de> Subject: [Haskell-beginners] Haskell type system To: beginners@haskell.org Message-ID: <20090927102249.gb4...@debian> Content-Type: text/plain; charset=us-ascii; format=flowed Hi, i am trying to understand the Haskell type system. I thought i understood it quite well until i encountered the three following exercises. As you can see, i have the answers already. But i don't understand, why they are correct. Could anybody tell me a good place where i could learn how to answers these kind of questions correctly or could give me some explanations, why these answers are correct? Any help is highly appreciated. Kind regards Chris Two functions f and g with the following signatures are given: f :: a -> a g :: b -> c -> b A) Give the type of the following expressions: 1) g [False] True :: 2) g [] True :: 3) g (f True) :: 4) g f :: Answers: 1 [Boolean] 2) [a] 3) c -> Bool 4) c -> (a -> a)1) g f 1 B) Which of the following statements is correct? 2) g (f 1) is type correct 3) g . (f 1) is type correct 4) g . f 1 is type correct 5) (g . f) 1 is type correct 6) none of the expressions is correct Answers: 1,2 and 5 are correct. C) A function h is given as: h p x = p (f x). Which of the following statements is correct. 1) h :: a -> b -> a -> b 2) h :: (a -> a) -> a -> a 3) h :: (a -> b) -> a -> b 4) h is equivalent to h' with h' p = p . f 5) h is equivalent to h' with h' p = p f 5) h is equivalent to h' with h' p x = p f x Answers: (I am not sure, if i remember correctly, but 3) and 4) should be correct.) ------------------------------ Message: 7 Date: Sun, 27 Sep 2009 14:50:53 +0200 From: Peter Verswyvelen <bugf...@gmail.com> Subject: Re: [Haskell-beginners] Haskell type system To: informationen <informatio...@gmx.de> Cc: beginners@haskell.org Message-ID: <a88790d10909270550x23499a1do2e525c71b30f7...@mail.gmail.com> Content-Type: text/plain; charset="iso-8859-1" Which parts would like explanations for? All of them? On Sun, Sep 27, 2009 at 12:22 PM, informationen <informatio...@gmx.de>wrote: > Hi, > > i am trying to understand the Haskell type system. I thought i understood > it > quite well until i encountered the three following exercises. As you can > see, i > have the answers already. But i don't understand, why they are correct. > > Could anybody tell me a good place where i could learn how to answers these > kind > of questions correctly or could give me some explanations, why these > answers are > correct? > > Any help is highly appreciated. > > Kind regards > > Chris > Two functions f and g with the following signatures are given: > f :: a -> a > g :: b -> c -> b > > A) Give the type of the following expressions: > > 1) g [False] True :: 2) g [] True :: 3) g (f True) :: 4) g f > :: > Answers: > > 1 [Boolean] 2) [a] 3) c -> Bool > 4) c -> (a -> a)1) g f 1 > B) Which of the following statements is correct? > > 2) g (f 1) is type correct > 3) g . (f 1) is type correct > 4) g . f 1 is type correct > 5) (g . f) 1 is type correct > 6) none of the expressions is correct > > Answers: > 1,2 and 5 are correct. > > C) A function h is given as: h p x = p (f x). Which of the following > statements is correct. > > 1) h :: a -> b -> a -> b > 2) h :: (a -> a) -> a -> a > 3) h :: (a -> b) -> a -> b > 4) h is equivalent to h' with h' p = p . f > 5) h is equivalent to h' with h' p = p f > 5) h is equivalent to h' with h' p x = p f x > > Answers: > (I am not sure, if i remember correctly, but 3) and 4) should be > correct.) > > > _______________________________________________ > Beginners mailing list > Beginners@haskell.org > http://www.haskell.org/mailman/listinfo/beginners > -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.haskell.org/pipermail/beginners/attachments/20090927/aaa65450/attachment.html ------------------------------ _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners End of Beginners Digest, Vol 15, Issue 16 *****************************************