Re: [Haskell-cafe] Type checking oddity -- maybe my own confusion
Ryan Newton wrote: The desired goal was that everywhere I construct a value using the Assign constructor, that the resulting value's type to be tainted by the AssignCap constraint. Your code essentially accomplishes the goal: data E m where Assign :: AssignCap m = V - E m - E m - E m Varref :: V - E m -- ... Every time you construct the value of the type (E m) with the Assign constructor, you have to constructively prove -- provide evidence for -- that the type m is a member of AssignCap. That evidence is stored within the E m value and so can be reused whenever it is needed later. Let us modify the example slightly: class AssignCap m class MutateCap m data E m where Assign :: AssignCap m = V - E m - E m - E m Mutate :: MutateCap m = V - E m - E m - E m Varref :: V - E m -- ... type V = String -- test1 :: E t - E t test1 (Assign v x1 x2) = Assign v x1 x2 -- test2 :: MutateCap t = E t - E t test2 (Assign v x1 x2) = Mutate v x1 x2 To use the constructor Assign, we need the evidence that AssignCap m holds. The deconstructed value (Assign v x1 x2) provides such an evidence (as a `hidden' field of the data type). Therefore, the inferred type for test1 has no constraints. In contrast, in test2 nothing provides Mutate with the evidence that MutateCap m holds. Therefore, the inferred type has the MutateCap m constraint. If storing the evidence is not desired, then one should use ordinary ADT with smart constructors: -- Data constructors should not be exported data E1 m = Assign1 V (E1 m) (E1 m) | Varref1 V isAssign (Assign1 v x1 x2) = Just (v,x1,x2) isAssign _ = Nothing assign :: AssignCap m = V - E1 m - E1 m - E1 m assign = Assign1 -- test3 :: AssignCap m = E1 m - E1 m test3 e | Just (v,x1,x2) - isAssign e = assign v x1 x2 OCaml has a so-called private constructors, which permit deconstruction but prohibit construction. They are quite handy, saving us trouble writing the views like isAssign. Actually... to go a bit further, I thought there was some way to arrange this so that, upon GHC type-checking the case statement, it would realize that certain cases are forbidden based on the type, and would consider the pattern match complete without them (or issue an error if they are present). The key word in the phrase ``certain cases are forbidden based on the type'' is _type_ -- rather than a type class. If you wish to use this special GADT feature, you have to `invert' your design. Rather than specifying what is _required_ to construct an (E m) value, you should specify what is _provided_. data E2 m where Assign2 :: V - E2 m - E2 m - E2 IOT Varref2 :: V - E2 PureT test4 :: E2 IOT - E2 IOT test4 (Assign2 v x1 x2) = Assign2 v x1 x2 test4 (Varref2 _) = undefined The compiler complaints Couldn't match type `IOT' with `PureT' Inaccessible code in a pattern with constructor Varref2 :: V - E2 PureT, in an equation for `test4' In the pattern: Varref2 _ In an equation for `test4': test4 (Varref2 _) = undefined as desired. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Baffling Hackage build log
This seems to be a general problem with the Hackage server as other packages uploaded after yours have failed to build with similar errors... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Seeking Don Stewart
Hello all, Sorry for the spam. I'm trying to get ahold of Don Stewart, but it looks like there's some hiccup at Galois. When I mail him I get: d...@galois.com: host mail.galois.com[69.30.63.196] said: 550 5.1.1 d...@galois.com... User unknown (in reply to RCPT TO command) Does anyone know what's up, or if there's another (non-emergency) way to get in touch with him? -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Seeking Don Stewart
Just post something on Stack Overflow, throw in a line about how inefficient Haskell is compared with Java. It's like his bat signal. Michael On Wed, Jul 13, 2011 at 12:09 PM, wren ng thornton w...@freegeek.org wrote: Hello all, Sorry for the spam. I'm trying to get ahold of Don Stewart, but it looks like there's some hiccup at Galois. When I mail him I get: d...@galois.com: host mail.galois.com[69.30.63.196] said: 550 5.1.1 d...@galois.com... User unknown (in reply to RCPT TO command) Does anyone know what's up, or if there's another (non-emergency) way to get in touch with him? -- Live well, ~wren ___ 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] Seeking Don Stewart
It's mine too! Who!? Who said that? Links! I want links! (And names) 2011/7/13 Michael Snoyman mich...@snoyman.com Just post something on Stack Overflow, throw in a line about how inefficient Haskell is compared with Java. It's like his bat signal. Michael On Wed, Jul 13, 2011 at 12:09 PM, wren ng thornton w...@freegeek.org wrote: Hello all, Sorry for the spam. I'm trying to get ahold of Don Stewart, but it looks like there's some hiccup at Galois. When I mail him I get: d...@galois.com: host mail.galois.com[69.30.63.196] said: 550 5.1.1 d...@galois.com... User unknown (in reply to RCPT TO command) Does anyone know what's up, or if there's another (non-emergency) way to get in touch with him? -- Live well, ~wren ___ 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 mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Seeking Don Stewart
Don isn't working at Galois anymore. I guess his new email address is simple to find but I gave it to Wren privately. But I guess the sloth signal works fine too. Cheers, Thu 2011/7/13 Yves Parès limestr...@gmail.com: It's mine too! Who!? Who said that? Links! I want links! (And names) 2011/7/13 Michael Snoyman mich...@snoyman.com Just post something on Stack Overflow, throw in a line about how inefficient Haskell is compared with Java. It's like his bat signal. Michael On Wed, Jul 13, 2011 at 12:09 PM, wren ng thornton w...@freegeek.org wrote: Hello all, Sorry for the spam. I'm trying to get ahold of Don Stewart, but it looks like there's some hiccup at Galois. When I mail him I get: d...@galois.com: host mail.galois.com[69.30.63.196] said: 550 5.1.1 d...@galois.com... User unknown (in reply to RCPT TO command) Does anyone know what's up, or if there's another (non-emergency) way to get in touch with him? -- Live well, ~wren ___ 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 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] Seeking Don Stewart
wren ng thornton wrote: Hello all, Sorry for the spam. I'm trying to get ahold of Don Stewart, but it looks like there's some hiccup at Galois. When I mail him I get: d...@galois.com: host mail.galois.com[69.30.63.196] said: 550 5.1.1 d...@galois.com... User unknown (in reply to RCPT TO command) Don recently left Galois and is now working for a bank in NYC. Find him on google+. Erik -- -- Erik de Castro Lopo http://www.mega-nerd.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Baffling Hackage build log
This seems to be a general problem with the Hackage server as other packages uploaded after yours have failed to build with similar errors... It seems one batch of builds was broken due to some failure in downloading the package index. I've re-run it. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Paid work available in functional web programming
First, I apologize in advance if this post is deemed off-topic. It's about Ur/Web, a statically typed, pure functional programming languages that is much influenced by Haskell. For instance, Ur/Web includes monadic IO and type classes. I write to mention briefly that I'm looking for people interested in writing Ur/Web programs for pay. Ur/Web is a DSL for building modern web applications, and I believe it is truly a secret weapon for that domain, and one that should appeal to many Haskell fans. I have one customer now for whom I'm leading a project to develop a particular web application, and I'd like to have more. The current project would benefit from more programming help, and I would also like to develop a network of people interested in future projects. More information on Ur/Web can be found here: http://www.impredicative.com/ur/ So, are you interested in being paid at least market rates to develop real web applications in a cool Haskell-like language, thus helping to push functional programming further into the real world? Might you have any leads for possible customers for this kind of work, possibly including start-ups that want to do in-house development using a cool language with close support from the language creator (which happens to be me!)? I would love to receive reply e-mails with positive answers to either question! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Seeking Don Stewart
Hi everyone, I'm working for Standard Chartered, based in New York (currently though, I'm in Singapore). You can reach me on this email. Cheers, Don On Wed, Jul 13, 2011 at 5:09 PM, wren ng thornton w...@freegeek.org wrote: Hello all, Sorry for the spam. I'm trying to get ahold of Don Stewart, but it looks like there's some hiccup at Galois. When I mail him I get: d...@galois.com: host mail.galois.com[69.30.63.196] said: 550 5.1.1 d...@galois.com... User unknown (in reply to RCPT TO command) Does anyone know what's up, or if there's another (non-emergency) way to get in touch with him? -- Live well, ~wren ___ 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] Paid work available in functional web programming
On 13 July 2011 15:28, Adam Chlipala ad...@impredicative.com wrote: I write to mention briefly that I'm looking for people interested in writing Ur/Web programs for pay. Ur/Web is a DSL for building modern web applications, and I believe it is truly a secret weapon for that domain, and one that should appeal to many Haskell fans. I have one customer now for whom I'm leading a project to develop a particular web application, and I'd like to have more. The current project would benefit from more programming help, and I would also like to develop a network of people interested in future projects. More information on Ur/Web can be found here: http://www.impredicative.com/ur/ I would like to see a real application in Ur/Web. There are many simple examples. I don't and wouldn't want to develop like that, writing raw HTML and SQL seems going backwards despite the incredible advances in consistency and correctness that Ur/Web offers. I also find it hard to understand the type system in a non-superficial level because the related paper was very hard to grok. I tried to get it running a while ago and could not get it to compile. I would also like to see how it handles non-web stuff as inevitably IME web applications involve more than merely reading and writing to a database. I like the idea, please keep us posted about it. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Paid work available in functional web programming
It'd also be interesting to know what you missed in Haskell web development so that you needed to build a new language inspired from it. 2011/7/13 Christopher Done chrisd...@googlemail.com On 13 July 2011 15:28, Adam Chlipala ad...@impredicative.com wrote: I write to mention briefly that I'm looking for people interested in writing Ur/Web programs for pay. Ur/Web is a DSL for building modern web applications, and I believe it is truly a secret weapon for that domain, and one that should appeal to many Haskell fans. I have one customer now for whom I'm leading a project to develop a particular web application, and I'd like to have more. The current project would benefit from more programming help, and I would also like to develop a network of people interested in future projects. More information on Ur/Web can be found here: http://www.impredicative.com/ur/ I would like to see a real application in Ur/Web. There are many simple examples. I don't and wouldn't want to develop like that, writing raw HTML and SQL seems going backwards despite the incredible advances in consistency and correctness that Ur/Web offers. I also find it hard to understand the type system in a non-superficial level because the related paper was very hard to grok. I tried to get it running a while ago and could not get it to compile. I would also like to see how it handles non-web stuff as inevitably IME web applications involve more than merely reading and writing to a database. I like the idea, please keep us posted about it. ___ 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] Splitting Hackage Packages and re-exporting entire modules (with same module name)
Antoine Latter wrote:
If you give the module a new name in the new package then the old
module can re-export all of the symbols in the new module.
In GHC I don't think there is a way for two packages to export the
same module and have them be recognized as the same thing, as far as I
know.
Right, but you don't have to rename the module if you use the
PackageImports extension. (Incidentally, this used by the haskell2010
ibrary, which is implemented in terms of base)
http://haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#package-imports
So the following should work, assuming 'original' is a package exporting
the Foo.Bar module.
{-# LANGUAGE PackageImports #-}
module Foo.Bar (module Original) where
import original Foo.Bar as Original
Best regards,
Bertram
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Re: [Haskell-cafe] Paid work available in functional web programming
I also think it would be really good to have some documentation that explains the type system and how to do neat things with it in terms that a reasonably competent haskell / ML programmer could understand. I played around with Ur/Web about a year ago and was able to make a simple application, and use some C libraries (the C FFI is really easy to use), but realized that I wasn't able to do much of anything beyond mimicking the demos in various ways, mainly because the documentation was so sparse (when I didn't know how to do something, I just tried to do what I would expect it to do if it were haskell, which worked a surprising amount of the time, but wasn't the most enjoyable experience). Looking at, for example, page 19 of the reference manual [1], which is supposed to explain how expressions are typed (which I would assume would give input into how the type system worked), I, probably like Chris, couldn't make much sense of it. Now I don't have a PhD in type theory, or even a masters degree, but if your intended audience includes people like me, the documentation definitely needs work! Now perhaps understanding those tables isn't actually important to using the language, but from looking through the manual / available documentation, there seems to be the really basic cookbook style stuff, that you can copy and paste and modify, as long as you are careful, then the source code itself, from which more can be gleaned, and then this type of type theory. Because of this (or until there is real documentation explaining some of the novel things about this language), I think Ur/Web is going to remain a cool thing that barely anyone can do anything with. Something to be linked in reddit or stack overflow posts, but not actually used! It seems like documentation of the really basic stuff is there, and the really advanced stuff (which is great, don't get me wrong), but the stuff in the middle is missing! Which is too bad, because it seems like it is doing some really exciting things. 1. http://www.impredicative.com/ur/manual.pdf On Jul 13, 2011, at 11:10 AM, Christopher Done wrote: On 13 July 2011 15:28, Adam Chlipala ad...@impredicative.com wrote: I write to mention briefly that I'm looking for people interested in writing Ur/Web programs for pay. Ur/Web is a DSL for building modern web applications, and I believe it is truly a secret weapon for that domain, and one that should appeal to many Haskell fans. I have one customer now for whom I'm leading a project to develop a particular web application, and I'd like to have more. The current project would benefit from more programming help, and I would also like to develop a network of people interested in future projects. More information on Ur/Web can be found here: http://www.impredicative.com/ur/ I would like to see a real application in Ur/Web. There are many simple examples. I don't and wouldn't want to develop like that, writing raw HTML and SQL seems going backwards despite the incredible advances in consistency and correctness that Ur/Web offers. I also find it hard to understand the type system in a non-superficial level because the related paper was very hard to grok. I tried to get it running a while ago and could not get it to compile. I would also like to see how it handles non-web stuff as inevitably IME web applications involve more than merely reading and writing to a database. I like the idea, please keep us posted about it. ___ 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] Splitting Hackage Packages and re-exporting entire modules (with same module name)
On Wed, Jul 13, 2011 at 10:31 AM, Bertram Felgenhauer
bertram.felgenha...@googlemail.com wrote:
Antoine Latter wrote:
If you give the module a new name in the new package then the old
module can re-export all of the symbols in the new module.
In GHC I don't think there is a way for two packages to export the
same module and have them be recognized as the same thing, as far as I
know.
Right, but you don't have to rename the module if you use the
PackageImports extension. (Incidentally, this used by the haskell2010
ibrary, which is implemented in terms of base)
http://haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#package-imports
So the following should work, assuming 'original' is a package exporting
the Foo.Bar module.
{-# LANGUAGE PackageImports #-}
module Foo.Bar (module Original) where
import original Foo.Bar as Original
Best regards,
Bertram
The downside to this approach is that anyone trying to use the module
in GHCi (or use the module in a non-Cabal setting) will need to
manually hide one of the packages.
Does anyone know if there is a way to make Cabal auto-hide a package
after install without too much trickery? That might be more than you
want to do.
Antoine
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Re: [Haskell-cafe] Paid work available in functional web programming
Christopher Done chrisd...@googlemail.com wrote: I write to mention briefly that I'm looking for people interested in writing Ur/Web programs for pay. Ur/Web is a DSL for building modern web applications, and I believe it is truly a secret weapon for that domain, and one that should appeal to many Haskell fans. I have one customer now for whom I'm leading a project to develop a particular web application, and I'd like to have more. The current project would benefit from more programming help, and I would also like to develop a network of people interested in future projects. I would like to see a real application in Ur/Web. There are many simple examples. I don't and wouldn't want to develop like that, writing raw HTML and SQL seems going backwards despite the incredible advances in consistency and correctness that Ur/Web offers. I agree about the HTML part, but not so much about the SQL part. Personally I went back from all the nice abstractions to writing raw SQL, because I realized that this is the only way to really exploit the power of my database system (PostgreSQL) [1]. [1] http://coder.mx/journal/yesod-persistent-vs-sql I also find it hard to understand the type system in a non-superficial level because the related paper was very hard to grok. I tried to get it running a while ago and could not get it to compile. I would also like to see how it handles non-web stuff as inevitably IME web applications involve more than merely reading and writing to a database. I like the idea, please keep us posted about it. I like the continuation part about it. If there were a web framework in Haskell similar to the continuation-based framework in Racket or Ur/Web, I would most certainly switch to it (from Yesod), given that it's mature enough. Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife = sex) http://ertes.de/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: fix-imports-0.1.2
On 12.07.2011 09:59, Evan Laforge wrote: I meant more in the Before: ... After: ... sense ;-) (i.e. visually being able to tell what your program does, rather than just a description). Oh, ok, I guess I can do that too: Before: module M where import ZZ.Out.Of.Order import qualified No.Longer.Needed as Needed -- x = Needed.y -- just removed this y = New.something -- just added this After: module M where import qualified Heavily.Nested.New as New import ZZ.Out.Of.Order -- x = Needed.y -- just removed this y = New.something -- just added this I also spend some time on managing imports. I'll try this program. However, usually I have a mix of qualified and unqualified imports, since some libraries are designed for unqualified imports. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: fix-imports-0.1.2
On Wed, Jul 13, 2011 at 12:08 PM, Henning Thielemann schlepp...@henning-thielemann.de wrote: I also spend some time on managing imports. I'll try this program. However, usually I have a mix of qualified and unqualified imports, since some libraries are designed for unqualified imports. You can still use unqualified imports, it just won't manage those for you. Automatically managing unqualified imports is solvable but harder. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Paid work available in functional web programming
Christopher Done wrote: I also find it hard to understand the type system in a non-superficial level because the related paper was very hard to grok. I'll only claim it's a fairly breezy read for people familiar with dependent type theory, which admittedly is not a huge crowd, even as a proportion of the Haskell community. More accessible documentation of that aspect is on my to-do list. I'm more or less waiting to start it until I get this current commercial project staffed properly. I know it _is_ possible to learn the interesting type system features well enough with just the existing documentation, because one programmer on the project, who has no CS research background, has managed to do it without much apparent trouble. I tried to get it running a while ago and could not get it to compile. You couldn't get the compiler to compile? No one has reported problems recently, so I suspect everything would Just Work today, if you're using Linux or OS X (and possibly in other cases). I would also like to see how it handles non-web stuff as inevitably IME web applications involve more than merely reading and writing to a database. I have no near-term plans to build an Ur implementation that handles non-web applications. There is an FFI, though. Yves_Pares wrote: It'd also be interesting to know what you missed in Haskell web development so that you needed to build a new language inspired from it. The key piece is precisely the basis of my paper Ur: Statically-Typed Metaprogramming with Type-Level Record Computation. Haskell is missing the features that I think are critical for pleasant type-level computation, in particular of the variety that I use in the examples detailed in the paper. I'll leave the rest of my argument to be read out of the paper by those with enough background to do so. Folks without that background might at least read the case studies part of the paper and consider how such things might be implemented in Haskell, with equivalent or stronger static guarantees. Ertugrul Soeylemez wrote: Christopher Donechrisd...@googlemail.com wrote: I write to mention briefly that I'm looking for people interested in writing Ur/Web programs for pay. Ur/Web is a DSL for building modern web applications, and I believe it is truly a secret weapon for that domain, and one that should appeal to many Haskell fans. I have one customer now for whom I'm leading a project to develop a particular web application, and I'd like to have more. The current project would benefit from more programming help, and I would also like to develop a network of people interested in future projects. I would like to see a real application in Ur/Web. There are many simple examples. I don't and wouldn't want to develop like that, writing raw HTML and SQL seems going backwards despite the incredible advances in consistency and correctness that Ur/Web offers. I agree about the HTML part, but not so much about the SQL part. Personally I went back from all the nice abstractions to writing raw SQL, because I realized that this is the only way to really exploit the power of my database system (PostgreSQL) [1]. I agree. I find that SQL is the most natural language for expressing data reading and writing, at least for the web applications I write. The need to go through a less declarative interface (e.g., classic ORMs) would be a bug, not a feature, for me. (Though the online Ur/Web demos include type-safe ORM implemented as a library completely within the language!) As far as HTML templating goes, templates are easy to implement as functions within Ur. I understand that people unfamiliar with the language will want to see code examples before accepting this, but unfortunately I have none now. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] [iteratee] empty chunk as special case of input
Hi community, hi John. I find myself reading bindIteratee[1] function for a several days.. there is something that keeps me away from completely understanding of the concept. The most noticeble thing is \nullC\ guard in the definition. To demonstate the consequences of this solution, let me define an iterator like myI = Iteratee $ \onDone _ - onDone 'a' (Chunk xyz) It is a bit unusial, since myI substitutes real stream with a fake one (xyz). Now lets define two actions producing different results in unusual manner: printI i = enumPure1Chunk ['a'..'g'] i = run = print i1 = (return 'b' myI I.head) -- myI substitutes the stream, last /I.head/ produces 'x', OK i2 = (I.head myI I.head) -- produces 'b'! I expected another 'x' here but myI's stream was ignored by = Well, I understand that this is probably an expected behaviour, but what is it for? Why we can't handle null input like non-null? Iterator may just stay in it's current state in that case. Thanks in advance Sergey -- [1] - bindIteratee (basically, =) code from Data.Iteratee.Base.hs bindIteratee :: (Monad m, Nullable s) = Iteratee s m a - (a - Iteratee s m b) - Iteratee s m b bindIteratee = self where self m f = Iteratee $ \onDone onCont - let m_done a (Chunk s) | nullC s = runIter (f a) onDone onCont m_done a stream = runIter (f a) (const . flip onDone stream) f_cont where f_cont k Nothing = runIter (k stream) onDone onCont f_cont k e = onCont k e in runIter m m_done (onCont . (flip self f .)) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: fix-imports-0.1.2
I have used it a little and it worked quite nicely. One thing that to look out for though is that it first checks for modules from the current directory down -- so running it in somewhere you happen to have ghc sources too, will have all that come with it imported from there (and lines like import path.to.ghc.DataMaybe (fromJust) added). But this probably happens only when testing the program in the root of your home directory... (The reason I'm not using it regularly is that I haven't figured out a good way to use it, when developing with Notepad++ over sftp in another environment) -- Markus Läll ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: fix-imports-0.1.2
On Wed, Jul 13, 2011 at 3:05 PM, Markus Läll markus.l...@gmail.com wrote: One thing that to look out for though is that it first checks for modules from the current directory down -- so running it in somewhere you happen to have ghc sources too, will have all that come with it imported from there (and lines like import path.to.ghc.DataMaybe (fromJust) added). But this probably happens only when testing the program in the root of your home directory... Yeah, currently the most annoying thing is when it guesses wrong. It's set up to work with my project, but you can tweak the search heuristic easily enough by editing findLocalModule. I'll have it skip non-capitalized directories, but a better solution is to not edit modules in your home directory :) (The reason I'm not using it regularly is that I haven't figured out a good way to use it, when developing with Notepad++ over sftp in another environment) Well, if anyone makes bindings for other editors, feel free to send a patch. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [iteratee] empty chunk as special case of input
Hi Sergey, iteratee (the package) uses a null chunk to signify that no further stream data is available within the iteratee, that is, at some point the stream has been entirely consumed. Therefore, if any of the composed iteratees haven't run to completion, they need to get more data from an enumerator. Thus 'bindIteratee' has the nullC guard in the definition as an optimization; there's no need to send the null chunk to bound iteratees because in most cases they won't be able to do anything with it. I've recently considered removing this, but at present when I take it out some unit tests fail and I haven't had time to explore further. Since this would have other benefits I would like to do so provided it doesn't strongly impact performance. Rather than simply removing the case I could add a null case to the Stream type, but that could cause some extra work for users. Also, one rule for writing iteratees is that they shouldn't put elements into the stream. Doing so may cause various transformers to behave incorrectly. If you want to modify a stream rather than simply consuming elements, the correct approach is to create an enumeratee (stream transformer). John L. On Wed, Jul 13, 2011 at 11:00 PM, Sergey Mironov ier...@gmail.com wrote: Hi community, hi John. I find myself reading bindIteratee[1] function for a several days.. there is something that keeps me away from completely understanding of the concept. The most noticeble thing is \nullC\ guard in the definition. To demonstate the consequences of this solution, let me define an iterator like myI = Iteratee $ \onDone _ - onDone 'a' (Chunk xyz) It is a bit unusial, since myI substitutes real stream with a fake one (xyz). Now lets define two actions producing different results in unusual manner: printI i = enumPure1Chunk ['a'..'g'] i = run = print i1 = (return 'b' myI I.head) -- myI substitutes the stream, last /I.head/ produces 'x', OK i2 = (I.head myI I.head) -- produces 'b'! I expected another 'x' here but myI's stream was ignored by = Well, I understand that this is probably an expected behaviour, but what is it for? Why we can't handle null input like non-null? Iterator may just stay in it's current state in that case. Thanks in advance Sergey -- [1] - bindIteratee (basically, =) code from Data.Iteratee.Base.hs bindIteratee :: (Monad m, Nullable s) = Iteratee s m a - (a - Iteratee s m b) - Iteratee s m b bindIteratee = self where self m f = Iteratee $ \onDone onCont - let m_done a (Chunk s) | nullC s = runIter (f a) onDone onCont m_done a stream = runIter (f a) (const . flip onDone stream) f_cont where f_cont k Nothing = runIter (k stream) onDone onCont f_cont k e = onCont k e in runIter m m_done (onCont . (flip self f .)) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [iteratee] empty chunk as special case of input
Sorry for the followup, but I forgot about one other important reason (probably the real reason) for the nullC case in bindIteratee. Note what happens in the regular case: the iteratee is run, and if it's in a completed state, the result is passed to the bound function (in the m_done line), which is then also run. Examine what happens if the inner iteratee is also complete: const . flip onDone stream which would be more clearly written as \b _str - onDone b stream so in this case the leftover stream result from the first iteratee (stream) is used as the result of the second iteratee, and the leftover stream from the second iteratee (_str) is discarded. This doesn't seem right; what should happen is that the two streams should be appended somehow. It works because at this stage an iteratee won't have been enumerated over (by the current stream at least), so it can't have any leftover data, just a null chunk. But bindIteratee explicitly checks for the null chunk case also so that's not a problem. If the iteratee was enumerated over by another stream and therefore does have leftover data, then since that data isn't part of the current stream it's rightfully discarded anyway. This is why your function produced an unexpected result; it's in a completed state without having been enumerated over, but also has leftover data, which bindIteratee ignores. Now that I've thought about it, I'm not convinced this is always correct; in particular I suspect it for being responsible for a slightly convoluted implementation of enumFromCallbackCatch. I'll have to expend more brain cells on it, I think. John L. On Thu, Jul 14, 2011 at 1:15 AM, John Lato jwl...@gmail.com wrote: Hi Sergey, iteratee (the package) uses a null chunk to signify that no further stream data is available within the iteratee, that is, at some point the stream has been entirely consumed. Therefore, if any of the composed iteratees haven't run to completion, they need to get more data from an enumerator. Thus 'bindIteratee' has the nullC guard in the definition as an optimization; there's no need to send the null chunk to bound iteratees because in most cases they won't be able to do anything with it. I've recently considered removing this, but at present when I take it out some unit tests fail and I haven't had time to explore further. Since this would have other benefits I would like to do so provided it doesn't strongly impact performance. Rather than simply removing the case I could add a null case to the Stream type, but that could cause some extra work for users. Also, one rule for writing iteratees is that they shouldn't put elements into the stream. Doing so may cause various transformers to behave incorrectly. If you want to modify a stream rather than simply consuming elements, the correct approach is to create an enumeratee (stream transformer). John L. On Wed, Jul 13, 2011 at 11:00 PM, Sergey Mironov ier...@gmail.com wrote: Hi community, hi John. I find myself reading bindIteratee[1] function for a several days.. there is something that keeps me away from completely understanding of the concept. The most noticeble thing is \nullC\ guard in the definition. To demonstate the consequences of this solution, let me define an iterator like myI = Iteratee $ \onDone _ - onDone 'a' (Chunk xyz) It is a bit unusial, since myI substitutes real stream with a fake one (xyz). Now lets define two actions producing different results in unusual manner: printI i = enumPure1Chunk ['a'..'g'] i = run = print i1 = (return 'b' myI I.head) -- myI substitutes the stream, last /I.head/ produces 'x', OK i2 = (I.head myI I.head) -- produces 'b'! I expected another 'x' here but myI's stream was ignored by = Well, I understand that this is probably an expected behaviour, but what is it for? Why we can't handle null input like non-null? Iterator may just stay in it's current state in that case. Thanks in advance Sergey -- [1] - bindIteratee (basically, =) code from Data.Iteratee.Base.hs bindIteratee :: (Monad m, Nullable s) = Iteratee s m a - (a - Iteratee s m b) - Iteratee s m b bindIteratee = self where self m f = Iteratee $ \onDone onCont - let m_done a (Chunk s) | nullC s = runIter (f a) onDone onCont m_done a stream = runIter (f a) (const . flip onDone stream) f_cont where f_cont k Nothing = runIter (k stream) onDone onCont f_cont k e = onCont k e in runIter m m_done (onCont . (flip self f .)) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
