- Beginners - Haskell.org

import not working
by Galaxy Being 06 Jun '21

06 Jun '21

I go to a directory. I run stack install Safe I start up ghci and get the Prelude prompt. I run import Safe and I get import Safe | ^^^^^^^^^^^ Failed, no modules loaded. I'm once again frustrated. I try to load this hs file {-# LANGUAGE ViewPatterns #-} {-# LANGUAGE NoMonomorphismRestriction #-} import Safe lookupDefault :: Eq a => a -> b -> [(a,b)] -> b lookupDefault k _ (lookup k -> Just s) = s lookupDefault _ d _ = d headTup :: (a, [t]) -> [t] headTup (headMay . snd -> Just n) = [n] headTup _ = [] headNil :: [a] -> [a] headNil (headMay -> Just x) = [x] headNil _ = [] with the same result. What do I need to do? -- ⨽ Lawrence Bottorff Grand Marais, MN, USA borgauf(a)gmail.com

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Re: [Haskell-beginners] import not working
by David McBride 05 Jun '21

05 Jun '21

Spam detection software, running on the system "mail.haskell.org", has identified this incoming email as possible spam. The original message has been attached to this so you can view it (if it isn't spam) or label similar future email. If you have any questions, see @@CONTACT_ADDRESS@@ for details. Content preview: safe is a non core package. You will have to install it by using the command stack exec --package safe ghci You can do that with multiple packages. And I believe you can write a shebang at the top of you're script so that these packages are installed automatically when you run the script. [...] Content analysis details: (5.0 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (toad3k[at]gmail.com) -0.0 SPF_PASS SPF: sender matches SPF record 5.0 UNWANTED_LANGUAGE_BODY BODY: Message written in an undesired language -1.9 BAYES_00 BODY: Bayes spam probability is 0 to 1% [score: 0.0000] 0.0 HTML_MESSAGE BODY: HTML included in message 0.0 T_DKIM_INVALID DKIM-Signature header exists but is not valid 1.9 FREEMAIL_REPLY From and body contain different freemails The original message was not completely plain text, and may be unsafe to open with some email clients; in particular, it may contain a virus, or confirm that your address can receive spam. If you wish to view it, it may be safer to save it to a file and open it with an editor.

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Data constraint?
by Galaxy Being 04 Jun '21

04 Jun '21

If I have a type type WaterChem = CaHardness NaturalChem | Alkalinity NaturalChem and I want to have the values of CaHardness and Alkalinity constrained to positive Int and between certain high and low values, I could do a newtype to creater a NaturalChem number, thus never less than 0, but what is the best practice to insure these values are between a certain range? Types in Haskell can't go that far, can they? Reading this <https://www.haskell.org/tutorial/moretypes.html> tells me I can have some of what I want. How are type values that need to be constrained handled best practices? Again, the type world of Haskell seems to do some of the lifting, but I'd like some advice if I want to have both of my constraints. -- ⨽ Lawrence Bottorff Grand Marais, MN, USA borgauf(a)gmail.com

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How to show the help page of a function
by Peng Yu 27 May '21

27 May '21

Hi, I want to check the help page of a function in haskell. For example, to check the help page of "many", could anybody help me know to get to its help page? Thanks. -- Regards, Peng

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(Online) Utrecht Summer School on Advanced functional programming
by Swierstra, W.S. (Wouter) 25 May '21

25 May '21

SUMMER SCHOOL ON ADVANCED FUNCTIONAL PROGRAMMING Online - 05-9 July 2021 http://www.afp.school # Call for Participation ## About The Advanced Functional Programming summer school has been running for more than ten years. We aim to educate aspiring Haskell programmers beyond the basic material covered by many textbooks. This year the course will be offered *online only*. A typical day will consist a 2-3 hours of lectures, sandwiched between supervised lab sessions. Lectures will be held in the (European) afternoon, but recordings will be made available if attending live is problematic. The lectures will cover several more advanced topics regarding programming with types in Haskell, including topics such as: * monads and applicative functors; * lambda calculus; * generalized algebraic datatypes; * datatype generic programming * type families and type-level programming; ## Lecturers Utrecht staff: * Gabriele Keller * Trevor McDonell * Wouter Swierstra ## Prerequisites We expect students to have a basic familiarity with Haskell already. You should be able to write recursive functions over algebraic data types, such as lists and trees. There is a great deal of material readily available that covers this material. If you've already started learning Haskell and are looking to take your functional programming skills to the next level, this is the course for you. Soft registration deadline: 1 June, 2021 School: 05-09 July, 2021 ## Costs 50 euro - Registration fee We ask ask participants to pay a small registration fee to cover some of our organizational expenses. If this is problematic for you *for whatever reason*, please let us know and we can waive your registration fee. ## Further information Further information, including instructions on how to register, is available on our website: http://www.afp.school

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Re: [Haskell-beginners] Beginners Digest, Vol 154, Issue 9
by Michael Turner 22 May '21

22 May '21

That did work, thank you. I wish instructions in the wiki included examples. A lot of my struggles as a newbie are with (1) cabal+stack, trying to conform to ways of doing things to get effects (e.g., perfect reproducibility) I don't even care about right now, and (2) documentation that doesn't tell you much about how to make things work. Regards, Michael Turner Executive Director Project Persephone 1-25-33 Takadanobaba Shinjuku-ku Tokyo 169-0075 Mobile: +81 (90) 5203-8682 turner(a)projectpersephone.org Understand - http://www.projectpersephone.org/ Join - http://www.facebook.com/groups/ProjectPersephone/ Donate - http://www.patreon.com/ProjectPersephone Volunteer - https://github.com/ProjectPersephone "Love does not consist in gazing at each other, but in looking outward together in the same direction." -- Antoine de Saint-Exupéry On Thu, May 20, 2021 at 9:08 PM <beginners-request(a)haskell.org> wrote: > > Send Beginners mailing list submissions to > beginners(a)haskell.org > > To subscribe or unsubscribe via the World Wide Web, visit > http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners > or, via email, send a message with subject or body 'help' to > beginners-request(a)haskell.org > > You can reach the person managing the list at > beginners-owner(a)haskell.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Beginners digest..." > > > Today's Topics: > > 1. Getting debugging going in ghci -- is there no mercy? > (Michael Turner) > 2. Re: Getting debugging going in ghci -- is there no mercy? > (Francesco Ariis) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Wed, 19 May 2021 21:10:50 +0900 > From: Michael Turner <michael.eugene.turner(a)gmail.com> > To: beginners(a)haskell.org > Subject: [Haskell-beginners] Getting debugging going in ghci -- is > there no mercy? > Message-ID: > <CANHeBig+dr+GRR-6vVGRHfOxKiEmA+Cff2+tfx+yr_=6cO8v0w(a)mail.gmail.com> > Content-Type: text/plain; charset="UTF-8" > > According to the Haskell wiki, "The trace function is located in the > base package", which encouraged me to think it should just work by > starting ghci. No such luck. So then I tried "stack gchi --package > debug". No such luck. I added packages to stack.yaml as suggested. And > here's where I am now. > > Of course, I'd like cookbook instructions, but I'm also including all > this error output to give people an idea of how incredibly > demoralizing the experience of being a newbie can be. As a newbie, > it's easy to get confused about what Haskell is actually doing. So > you'd naturally like a way to inspect intermediate results. Which > means you'd like tracing and debugging. > > Why is it so hard to get there? > > ----------- > > > C:\Users\Michael Turner\aug\aug.cabal was modified manually. Ignoring > C:\Users\Michael Turner\aug\package.yaml in favor of the cabal file. > If you want to use the package.yaml file instead of the cabal file, > then please delete the cabal file. > > Using main module: 1. Package `aug' component aug:exe:aug-exe with > main-is file: C:\Users\Michael Turner\aug\app\Main.hs > WARNING: Ignoring transformers-compat's bounds on transformers (>=0.3 > && ==0.2.*); using transformers-0.5.6.2. > Reason: allow-newer enabled. > > Error: While constructing the build plan, the following exceptions were > encountered: > > In the dependencies for Hoed-0.5.1: > QuickCheck needed, but the stack configuration has no specified version > (latest matching version is 2.14.2) > cereal needed, but the stack configuration has no specified version (latest > matching version is 0.5.8.1) > cereal-text needed, but the stack configuration has no specified version > (latest matching version is 0.1.0.2) > cereal-vector needed, but the stack configuration has no specified version > (latest matching version is 0.2.0.1) > primitive needed, but the stack configuration has no specified version > (latest matching version is 0.7.1.0) > regex-tdfa needed, but the stack configuration has no specified version > (latest matching version is 1.3.1.0) > regex-tdfa-text needed, but the stack configuration has no specified version > (latest matching version is 1.0.0.3) > semigroups needed, but the stack configuration has no specified version > (latest matching version is 0.19.1) > strict needed, but the stack configuration has no specified version (latest > matching version is 0.4.0.1) > terminal-size needed, but the stack configuration has no specified version > (latest matching version is 0.3.2.1) > vector-th-unbox needed, but the stack configuration has no specified version > (latest matching version is 0.2.1.9) > needed due to debug-0.1.1 -> Hoed-0.5.1 > > In the dependencies for aeson-1.5.6.0: > attoparsec must match >=0.13.2.2 && <0.15, but the stack > configuration has no > specified version (latest matching version is 0.14.1) > base-compat-batteries must match >=0.10.0 && <0.12, but the stack > configuration has no specified version > (latest matching > version is 0.11.2) > data-fix must match >=0.3 && <0.4, but the stack configuration has no > specified version (latest matching version is 0.3.1) > dlist must match >=0.8.0.4 && <1.1, but the stack configuration has no > specified version (latest matching version is 1.0) > primitive must match >=0.7.0.1 && <0.8, but the stack configuration has no > specified version (latest matching version is 0.7.1.0) > scientific must match >=0.3.6.2 && <0.4, but the stack configuration has no > specified version (latest matching version is 0.3.6.2) > strict must match >=0.4 && <0.5, but the stack configuration has > no specified > version (latest matching version is 0.4.0.1) > tagged must match >=0.8.6 && <0.9, but the stack configuration has no > specified version (latest matching version is 0.8.6.1) > th-abstraction must match >=0.2.8.0 && <0.5, but the stack configuration has > no specified version (latest matching version is 0.4.2.0) > these must match >=1.1 && <1.2, but the stack configuration has no specified > version (latest matching version is 1.1.1.1) > time-compat must match >=1.9.4 && <1.10, but the stack configuration has no > specified version (latest matching version is 1.9.5) > uuid-types must match >=1.0.3 && <1.1, but the stack configuration has no > specified version (latest matching version is 1.0.5) > needed due to debug-0.1.1 -> aeson-1.5.6.0 > > In the dependencies for libgraph-1.14: > monads-tf needed, but the stack configuration has no specified version > (latest matching version is 0.1.0.3) > union-find must match >=0.2, but the stack configuration has no specified > version (latest matching version is 0.2) > needed due to debug-0.1.1 -> libgraph-1.14 > > In the dependencies for prettyprinter-compat-ansi-wl-pprint-1.0.1: > prettyprinter-ansi-terminal must match >=1.1 && <1.2, but the stack > configuration has no specified version (latest > matching version is 1.1.2) > needed due to debug-0.1.1 -> prettyprinter-compat-ansi-wl-pprint-1.0.1 > > In the dependencies for uniplate-1.6.13: > syb needed, but the stack configuration has no specified version (latest > matching version is 0.7.2.1) > needed due to debug-0.1.1 -> uniplate-1.6.13 > > In the dependencies for vector-0.12.3.0: > primitive must match >=0.6.4.0 && <0.8, but the stack configuration has no > specified version (latest matching version is 0.7.1.0) > needed due to debug-0.1.1 -> vector-0.12.3.0 > > In the dependencies for yaml-0.11.5.0: > attoparsec must match >=0.11.3.0, but the stack configuration has > no specified > version (latest matching version is 0.14.1) > conduit must match >=1.2.8 && <1.4, but the stack configuration has no > specified version (latest matching version is 1.3.4.1) > libyaml must match >=0.1 && <0.2, but the stack configuration has > no specified > version (latest matching version is 0.1.2) > resourcet must match >=0.3 && <1.3, but the stack configuration has no > specified version (latest matching version is 1.2.4.2) > scientific must match >=0.3, but the stack configuration has no specified > version (latest matching version is 0.3.6.2) > needed due to debug-0.1.1 -> yaml-0.11.5.0 > > Some different approaches to resolving this: > > * Recommended action: try adding the following to your extra-deps > in C:\Users\Michael Turner\aug\stack.yaml: > > - QuickCheck-2.14.2@sha256:4ce29211223d5e6620ebceba34a3ca9ccf1c10c0cf387d48aea45599222ee5aa,7736 > - attoparsec-0.14.1@sha256:5a11f0339fb7e65429683e8a36d44adca3fd8cd40704525969c691e359c48fa0,5966 > - base-compat-batteries-0.11.2@sha256:eb3b976007754ddc16e8d4afacdd1e575ae746edb57dcd0a1a728ccd4b372a69,8804 > - cereal-0.5.8.1@sha256:37cb7a78c84412e94592a658768320c41f015f2b8707a433de835afb8ebc18d7,2767 > - cereal-text-0.1.0.2@sha256:dc10e00d9e5047d16a129682aac42c95da188d22e9f85856add051b9ace539c3,1349 > - cereal-vector-0.2.0.1@sha256:26d8e359f4c0de6dc06bf29f1cc2805847cdd8576d9f1598ecb263a1ca372bec,1116 > - conduit-1.3.4.1@sha256:eeabaf3f822e3e15317995766f50ef4a20371bdc3bb4721a7541e37228018dcf,5129 > - data-fix-0.3.1@sha256:7aee2c0633632479cef93c8000befd5bc950ba7c329d69e918ca520944164e27,1645 > - dlist-1.0@sha256:124cb3aa1decebd5171b46601b1f74cca6cfae12d266ace3799b86dd05ef7cb4,3560 > - libyaml-0.1.2@sha256:7f14f69ceb14659699974e8e47e1ea6f226ea21ff42a802db03e721c319d201d,2125 > - monads-tf-0.1.0.3@sha256:25b5d97af98adf7eca709c57f159c6c24c773cbb30e153abaeb156d81a451195,1427 > - prettyprinter-ansi-terminal-1.1.2@sha256:90b3b7650bc5b9f0e58da43621d23c817acfc0cf5ce71244b9bd11b8c9f95e3a,2653 > - primitive-0.7.1.0@sha256:29de6bfd0cf8ba023ceb806203dfbec0e51e3524e75ffe41056f70b4229c6f0f,2728 > - regex-tdfa-1.3.1.0@sha256:eb8d0f007cf45faca8574f56f0d19c9b02bc529ef1688d8f8a9751ce7dc36cc3,6483 > - regex-tdfa-text-1.0.0.3@sha256:fb72123627eadf43dd5ca74a2896940d50aac291e61f62177960f0563f7d5c03,1180 > - resourcet-1.2.4.2@sha256:d57516781d1721f70aa0b9ec8ea9200ab02bf76349cb76d73ad57729302289cc,1730 > - scientific-0.3.6.2@sha256:dd49abc76bd8e2b57e7a057dc2bb742a00527b4bf9350f9374be03b5934e55d8,4679 > - semigroups-0.19.1@sha256:ecae129621e0d2f77bef2f01e4458c2e0567ab6e1f39579c61d7cec8058ebb0e,6262 > - strict-0.4.0.1@sha256:08cf72ad570fddfe3b3424117bf20a303a1fb21047b40c1d6c8004c0e3e02a0b,4124 > - syb-0.7.2.1@sha256:bf42655a213402215299e435c52f799e76cbec0b984cd7153d6b9af8a1c0803f,3815 > - tagged-0.8.6.1@sha256:5ddf1e324c3cd644f097a48bf490f0bedf467f723fd240afb3ab3b750577f8e7,2874 > - terminal-size-0.3.2.1@sha256:7b2d8e0475a46961d07ddfb91dee618de70eff55d9ba0402ebeac1f9dcf9b18b,1259 > - th-abstraction-0.4.2.0@sha256:6ba7b201931f614173755f060fdf98f02095df68c1f7bc3e2691cf9d443e81f9,2194 > - these-1.1.1.1@sha256:e981c65228db5ae77a043631f74a1e4a4b770f7213866f584e3476b52512f1af,2631 > - time-compat-1.9.5@sha256:a586bd5a59b47ea0c9eafc55c6936ede11126f4a6e619d6d7aeefee73c43d9b8,4954 > - union-find-0.2@sha256:22e97cd9aeb8c96bf7cd8d359d4eda635dc0e0a6cd91b9a07e5a203b00949c8d,1232 > - uuid-types-1.0.5@sha256:5031383749d57cb95877d7e56f0300be66652b6e57f5ba6681dcc6e4f78d046d,2541 > - vector-th-unbox-0.2.1.9@sha256:5723d9c8a8a941dfeeb59dc42b84b924e4548ab6b5a4afe5b62b39f54667c2dd,1520 > > > Error: Plan construction failed. > > Warning: Build failed, but trying to launch GHCi anyway > The following GHC options are incompatible with GHCi and have not been > passed to it: -threaded > Configuring GHCi with the following packages: aug > > * * * * * * * * > > Warning: Multiple files use the same module name: > * Paths_aug found at the following paths > * C:\Users\Michael > Turner\aug\.stack-work\dist\e626a42b\build\aug-exe\autogen\Paths_aug.hs > (aug:exe:aug-exe) > * C:\Users\Michael > Turner\aug\.stack-work\dist\e626a42b\build\autogen\Paths_aug.hs > (aug:lib) > * * * * * * * * > > GHCi, version 8.6.5: http://www.haskell.org/ghc/ :? for help > <command line>: cannot satisfy -package debug > (use -v for more information) > > > Regards, > Michael Turner > Executive Director > Project Persephone > 1-25-33 Takadanobaba > Shinjuku-ku Tokyo 169-0075 > Mobile: +81 (90) 5203-8682 > turner(a)projectpersephone.org > > Understand - http://www.projectpersephone.org/ > Join - http://www.facebook.com/groups/ProjectPersephone/ > Donate - http://www.patreon.com/ProjectPersephone > Volunteer - https://github.com/ProjectPersephone > > "Love does not consist in gazing at each other, but in looking outward > together in the same direction." -- Antoine de Saint-Exupéry > > > ------------------------------ > > Message: 2 > Date: Wed, 19 May 2021 14:34:28 +0200 > From: Francesco Ariis <fa-ml(a)ariis.it> > To: beginners(a)haskell.org > Subject: Re: [Haskell-beginners] Getting debugging going in ghci -- is > there no mercy? > Message-ID: <20210519123428.GA29827@extensa> > Content-Type: text/plain; charset=utf-8 > > Il 19 maggio 2021 alle 21:10 Michael Turner ha scritto: > > According to the Haskell wiki, "The trace function is located in the > > base package", which encouraged me to think it should just work by > > starting ghci. No such luck. So then I tried "stack gchi --package > > debug". No such luck. I added packages to stack.yaml as suggested. And > > here's where I am now. > > λ> :m +Debug.Trace > λ> :t +d trace "prova" 234 > trace "prova" 234 :: Integer > λ> trace "prova" 234 > prova > 234 > > `debug` is an — excellent! — debug package by Neil Mitchell, but > not related to `Debug.Trace`. > > > > ------------------------------ > > Subject: Digest Footer > > _______________________________________________ > Beginners mailing list > Beginners(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners > > > ------------------------------ > > End of Beginners Digest, Vol 154, Issue 9 > *****************************************

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Getting debugging going in ghci -- is there no mercy?
by Michael Turner 19 May '21

19 May '21

According to the Haskell wiki, "The trace function is located in the base package", which encouraged me to think it should just work by starting ghci. No such luck. So then I tried "stack gchi --package debug". No such luck. I added packages to stack.yaml as suggested. And here's where I am now. Of course, I'd like cookbook instructions, but I'm also including all this error output to give people an idea of how incredibly demoralizing the experience of being a newbie can be. As a newbie, it's easy to get confused about what Haskell is actually doing. So you'd naturally like a way to inspect intermediate results. Which means you'd like tracing and debugging. Why is it so hard to get there? ----------- C:\Users\Michael Turner\aug\aug.cabal was modified manually. Ignoring C:\Users\Michael Turner\aug\package.yaml in favor of the cabal file. If you want to use the package.yaml file instead of the cabal file, then please delete the cabal file. Using main module: 1. Package `aug' component aug:exe:aug-exe with main-is file: C:\Users\Michael Turner\aug\app\Main.hs WARNING: Ignoring transformers-compat's bounds on transformers (>=0.3 && ==0.2.*); using transformers-0.5.6.2. Reason: allow-newer enabled. Error: While constructing the build plan, the following exceptions were encountered: In the dependencies for Hoed-0.5.1: QuickCheck needed, but the stack configuration has no specified version (latest matching version is 2.14.2) cereal needed, but the stack configuration has no specified version (latest matching version is 0.5.8.1) cereal-text needed, but the stack configuration has no specified version (latest matching version is 0.1.0.2) cereal-vector needed, but the stack configuration has no specified version (latest matching version is 0.2.0.1) primitive needed, but the stack configuration has no specified version (latest matching version is 0.7.1.0) regex-tdfa needed, but the stack configuration has no specified version (latest matching version is 1.3.1.0) regex-tdfa-text needed, but the stack configuration has no specified version (latest matching version is 1.0.0.3) semigroups needed, but the stack configuration has no specified version (latest matching version is 0.19.1) strict needed, but the stack configuration has no specified version (latest matching version is 0.4.0.1) terminal-size needed, but the stack configuration has no specified version (latest matching version is 0.3.2.1) vector-th-unbox needed, but the stack configuration has no specified version (latest matching version is 0.2.1.9) needed due to debug-0.1.1 -> Hoed-0.5.1 In the dependencies for aeson-1.5.6.0: attoparsec must match >=0.13.2.2 && <0.15, but the stack configuration has no specified version (latest matching version is 0.14.1) base-compat-batteries must match >=0.10.0 && <0.12, but the stack configuration has no specified version (latest matching version is 0.11.2) data-fix must match >=0.3 && <0.4, but the stack configuration has no specified version (latest matching version is 0.3.1) dlist must match >=0.8.0.4 && <1.1, but the stack configuration has no specified version (latest matching version is 1.0) primitive must match >=0.7.0.1 && <0.8, but the stack configuration has no specified version (latest matching version is 0.7.1.0) scientific must match >=0.3.6.2 && <0.4, but the stack configuration has no specified version (latest matching version is 0.3.6.2) strict must match >=0.4 && <0.5, but the stack configuration has no specified version (latest matching version is 0.4.0.1) tagged must match >=0.8.6 && <0.9, but the stack configuration has no specified version (latest matching version is 0.8.6.1) th-abstraction must match >=0.2.8.0 && <0.5, but the stack configuration has no specified version (latest matching version is 0.4.2.0) these must match >=1.1 && <1.2, but the stack configuration has no specified version (latest matching version is 1.1.1.1) time-compat must match >=1.9.4 && <1.10, but the stack configuration has no specified version (latest matching version is 1.9.5) uuid-types must match >=1.0.3 && <1.1, but the stack configuration has no specified version (latest matching version is 1.0.5) needed due to debug-0.1.1 -> aeson-1.5.6.0 In the dependencies for libgraph-1.14: monads-tf needed, but the stack configuration has no specified version (latest matching version is 0.1.0.3) union-find must match >=0.2, but the stack configuration has no specified version (latest matching version is 0.2) needed due to debug-0.1.1 -> libgraph-1.14 In the dependencies for prettyprinter-compat-ansi-wl-pprint-1.0.1: prettyprinter-ansi-terminal must match >=1.1 && <1.2, but the stack configuration has no specified version (latest matching version is 1.1.2) needed due to debug-0.1.1 -> prettyprinter-compat-ansi-wl-pprint-1.0.1 In the dependencies for uniplate-1.6.13: syb needed, but the stack configuration has no specified version (latest matching version is 0.7.2.1) needed due to debug-0.1.1 -> uniplate-1.6.13 In the dependencies for vector-0.12.3.0: primitive must match >=0.6.4.0 && <0.8, but the stack configuration has no specified version (latest matching version is 0.7.1.0) needed due to debug-0.1.1 -> vector-0.12.3.0 In the dependencies for yaml-0.11.5.0: attoparsec must match >=0.11.3.0, but the stack configuration has no specified version (latest matching version is 0.14.1) conduit must match >=1.2.8 && <1.4, but the stack configuration has no specified version (latest matching version is 1.3.4.1) libyaml must match >=0.1 && <0.2, but the stack configuration has no specified version (latest matching version is 0.1.2) resourcet must match >=0.3 && <1.3, but the stack configuration has no specified version (latest matching version is 1.2.4.2) scientific must match >=0.3, but the stack configuration has no specified version (latest matching version is 0.3.6.2) needed due to debug-0.1.1 -> yaml-0.11.5.0 Some different approaches to resolving this: * Recommended action: try adding the following to your extra-deps in C:\Users\Michael Turner\aug\stack.yaml: - QuickCheck-2.14.2@sha256:4ce29211223d5e6620ebceba34a3ca9ccf1c10c0cf387d48aea45599222ee5aa,7736 - attoparsec-0.14.1@sha256:5a11f0339fb7e65429683e8a36d44adca3fd8cd40704525969c691e359c48fa0,5966 - base-compat-batteries-0.11.2@sha256:eb3b976007754ddc16e8d4afacdd1e575ae746edb57dcd0a1a728ccd4b372a69,8804 - cereal-0.5.8.1@sha256:37cb7a78c84412e94592a658768320c41f015f2b8707a433de835afb8ebc18d7,2767 - cereal-text-0.1.0.2@sha256:dc10e00d9e5047d16a129682aac42c95da188d22e9f85856add051b9ace539c3,1349 - cereal-vector-0.2.0.1@sha256:26d8e359f4c0de6dc06bf29f1cc2805847cdd8576d9f1598ecb263a1ca372bec,1116 - conduit-1.3.4.1@sha256:eeabaf3f822e3e15317995766f50ef4a20371bdc3bb4721a7541e37228018dcf,5129 - data-fix-0.3.1@sha256:7aee2c0633632479cef93c8000befd5bc950ba7c329d69e918ca520944164e27,1645 - dlist-1.0@sha256:124cb3aa1decebd5171b46601b1f74cca6cfae12d266ace3799b86dd05ef7cb4,3560 - libyaml-0.1.2@sha256:7f14f69ceb14659699974e8e47e1ea6f226ea21ff42a802db03e721c319d201d,2125 - monads-tf-0.1.0.3@sha256:25b5d97af98adf7eca709c57f159c6c24c773cbb30e153abaeb156d81a451195,1427 - prettyprinter-ansi-terminal-1.1.2@sha256:90b3b7650bc5b9f0e58da43621d23c817acfc0cf5ce71244b9bd11b8c9f95e3a,2653 - primitive-0.7.1.0@sha256:29de6bfd0cf8ba023ceb806203dfbec0e51e3524e75ffe41056f70b4229c6f0f,2728 - regex-tdfa-1.3.1.0@sha256:eb8d0f007cf45faca8574f56f0d19c9b02bc529ef1688d8f8a9751ce7dc36cc3,6483 - regex-tdfa-text-1.0.0.3@sha256:fb72123627eadf43dd5ca74a2896940d50aac291e61f62177960f0563f7d5c03,1180 - resourcet-1.2.4.2@sha256:d57516781d1721f70aa0b9ec8ea9200ab02bf76349cb76d73ad57729302289cc,1730 - scientific-0.3.6.2@sha256:dd49abc76bd8e2b57e7a057dc2bb742a00527b4bf9350f9374be03b5934e55d8,4679 - semigroups-0.19.1@sha256:ecae129621e0d2f77bef2f01e4458c2e0567ab6e1f39579c61d7cec8058ebb0e,6262 - strict-0.4.0.1@sha256:08cf72ad570fddfe3b3424117bf20a303a1fb21047b40c1d6c8004c0e3e02a0b,4124 - syb-0.7.2.1@sha256:bf42655a213402215299e435c52f799e76cbec0b984cd7153d6b9af8a1c0803f,3815 - tagged-0.8.6.1@sha256:5ddf1e324c3cd644f097a48bf490f0bedf467f723fd240afb3ab3b750577f8e7,2874 - terminal-size-0.3.2.1@sha256:7b2d8e0475a46961d07ddfb91dee618de70eff55d9ba0402ebeac1f9dcf9b18b,1259 - th-abstraction-0.4.2.0@sha256:6ba7b201931f614173755f060fdf98f02095df68c1f7bc3e2691cf9d443e81f9,2194 - these-1.1.1.1@sha256:e981c65228db5ae77a043631f74a1e4a4b770f7213866f584e3476b52512f1af,2631 - time-compat-1.9.5@sha256:a586bd5a59b47ea0c9eafc55c6936ede11126f4a6e619d6d7aeefee73c43d9b8,4954 - union-find-0.2@sha256:22e97cd9aeb8c96bf7cd8d359d4eda635dc0e0a6cd91b9a07e5a203b00949c8d,1232 - uuid-types-1.0.5@sha256:5031383749d57cb95877d7e56f0300be66652b6e57f5ba6681dcc6e4f78d046d,2541 - vector-th-unbox-0.2.1.9@sha256:5723d9c8a8a941dfeeb59dc42b84b924e4548ab6b5a4afe5b62b39f54667c2dd,1520 Error: Plan construction failed. Warning: Build failed, but trying to launch GHCi anyway The following GHC options are incompatible with GHCi and have not been passed to it: -threaded Configuring GHCi with the following packages: aug * * * * * * * * Warning: Multiple files use the same module name: * Paths_aug found at the following paths * C:\Users\Michael Turner\aug\.stack-work\dist\e626a42b\build\aug-exe\autogen\Paths_aug.hs (aug:exe:aug-exe) * C:\Users\Michael Turner\aug\.stack-work\dist\e626a42b\build\autogen\Paths_aug.hs (aug:lib) * * * * * * * * GHCi, version 8.6.5: http://www.haskell.org/ghc/ :? for help <command line>: cannot satisfy -package debug (use -v for more information) Regards, Michael Turner Executive Director Project Persephone 1-25-33 Takadanobaba Shinjuku-ku Tokyo 169-0075 Mobile: +81 (90) 5203-8682 turner(a)projectpersephone.org Understand - http://www.projectpersephone.org/ Join - http://www.facebook.com/groups/ProjectPersephone/ Donate - http://www.patreon.com/ProjectPersephone Volunteer - https://github.com/ProjectPersephone "Love does not consist in gazing at each other, but in looking outward together in the same direction." -- Antoine de Saint-Exupéry

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Re: [Haskell-beginners] Beginners Digest, Vol 154, Issue 7
by Michael Turner 19 May '21

19 May '21

Ah, thank you. I just went with the more up-to-date version of the code, and didn't look at the original. Regards, Michael Turner Executive Director Project Persephone 1-25-33 Takadanobaba Shinjuku-ku Tokyo 169-0075 Mobile: +81 (90) 5203-8682 turner(a)projectpersephone.org Understand - http://www.projectpersephone.org/ Join - http://www.facebook.com/groups/ProjectPersephone/ Donate - http://www.patreon.com/ProjectPersephone Volunteer - https://github.com/ProjectPersephone "Love does not consist in gazing at each other, but in looking outward together in the same direction." -- Antoine de Saint-Exupéry On Tue, May 18, 2021 at 9:06 PM <beginners-request(a)haskell.org> wrote: > > Send Beginners mailing list submissions to > beginners(a)haskell.org > > To subscribe or unsubscribe via the World Wide Web, visit > http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners > or, via email, send a message with subject or body 'help' to > beginners-request(a)haskell.org > > You can reach the person managing the list at > beginners-owner(a)haskell.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Beginners digest..." > > > Today's Topics: > > 1. Type inference or just ... a typo in a paper? (Michael Turner) > 2. Re: Type inference or just ... a typo in a paper? > (Francesco Ariis) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Tue, 18 May 2021 17:24:37 +0900 > From: Michael Turner <michael.eugene.turner(a)gmail.com> > To: beginners(a)haskell.org > Subject: [Haskell-beginners] Type inference or just ... a typo in a > paper? > Message-ID: > <CANHeBigjUrGkKJAr44PS9WYATQDwvjNdWM_zC9DYcvcfA_dMaA(a)mail.gmail.com> > Content-Type: text/plain; charset="UTF-8" > > I've inherited some Haskell code, which you can find here: > > http://web.cecs.pdx.edu/~mpj/pubs/aug.html > > The text of the accompanying paper says, "we extend the Text class..." > -- but the identifier "Text" appears nowhere in the code. Is this just > an error in the paper, or is the Text class getting involved in some > indirect way, e.g. through String or perhaps because of the line > "instance Show Tree where . . ."? > > > Regards, > Michael Turner > Executive Director > Project Persephone > 1-25-33 Takadanobaba > Shinjuku-ku Tokyo 169-0075 > Mobile: +81 (90) 5203-8682 > turner(a)projectpersephone.org > > Understand - http://www.projectpersephone.org/ > Join - http://www.facebook.com/groups/ProjectPersephone/ > Donate - http://www.patreon.com/ProjectPersephone > Volunteer - https://github.com/ProjectPersephone > > "Love does not consist in gazing at each other, but in looking outward > together in the same direction." -- Antoine de Saint-Exupéry > > > ------------------------------ > > Message: 2 > Date: Tue, 18 May 2021 13:30:58 +0200 > From: Francesco Ariis <fa-ml(a)ariis.it> > To: beginners(a)haskell.org > Subject: Re: [Haskell-beginners] Type inference or just ... a typo in > a paper? > Message-ID: <20210518113058.GB879@extensa> > Content-Type: text/plain; charset=utf-8 > > Hello Michael, > > Il 18 maggio 2021 alle 17:24 Michael Turner ha scritto: > > I've inherited some Haskell code, which you can find here: > > > > http://web.cecs.pdx.edu/~mpj/pubs/aug.html > > > > The text of the accompanying paper says, "we extend the Text class..." > > -- but the identifier "Text" appears nowhere in the code. Is this just > > an error in the paper, or is the Text class getting involved in some > > indirect way, e.g. through String or perhaps because of the line > > "instance Show Tree where . . ."? > > In the updated source (`augupdated.hs`) that is missing, but in the > /original/ one (`aug.hs`) I read at line 255 > > instance Text Tree where > > Which was then replaced with: > > instance Show Tree where > > in the updated version. > > Weird to know something like `Show` was not named like that in the early > nineties! > —F > > > ------------------------------ > > Subject: Digest Footer > > _______________________________________________ > Beginners mailing list > Beginners(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners > > > ------------------------------ > > End of Beginners Digest, Vol 154, Issue 7 > *****************************************

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Type inference or just ... a typo in a paper?
by Michael Turner 18 May '21

18 May '21

I've inherited some Haskell code, which you can find here: http://web.cecs.pdx.edu/~mpj/pubs/aug.html The text of the accompanying paper says, "we extend the Text class..." -- but the identifier "Text" appears nowhere in the code. Is this just an error in the paper, or is the Text class getting involved in some indirect way, e.g. through String or perhaps because of the line "instance Show Tree where . . ."? Regards, Michael Turner Executive Director Project Persephone 1-25-33 Takadanobaba Shinjuku-ku Tokyo 169-0075 Mobile: +81 (90) 5203-8682 turner(a)projectpersephone.org Understand - http://www.projectpersephone.org/ Join - http://www.facebook.com/groups/ProjectPersephone/ Donate - http://www.patreon.com/ProjectPersephone Volunteer - https://github.com/ProjectPersephone "Love does not consist in gazing at each other, but in looking outward together in the same direction." -- Antoine de Saint-Exupéry

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Function to compute the mean
by Joe King 14 May '21

14 May '21

Greeetings I am new here and pretty new to Haskell. I was wondering what are the relative advanatges/disadvatnages of specifying a mean function in these two ways: mean :: [Double] -> Double mean xs = sum xs / fromIntegral (length xs) and mean1 :: (Real a, Fractional b) => [a] -> b mean1 xs = realToFrac (sum xs) / genericLength xs I understand that mean1 has the advantage that it can be called with lists of any Real type, so would work with things like foo :: [Int] foo = [1,2,3] mean foo -- type mismatch error mean1 foo -- no error But suppose that I know I will only ever use lists of Double, is there still any advantage (or disadvantage of using mean1). For example is there any performance benefit by using mean in that case since mean1 has additional function evaluation. Are there any other considerations ? Thanks in advance JK

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