- Beginners - Haskell.org

(Online) Utrecht Summer School on Advanced functional programming
by Swierstra, W.S. (Wouter) 26 May '21

26 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%2Bdr%2BGRR-6vVGRHfOxKiEmA%2BCff2%2Btfx%2Byr_%3D6cO8v0w(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 > *****************************************

1 0

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

2 1

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

4 7

Strange use of undefined (et al.) in list comprehension
by Galaxy Being 11 Apr '21

11 Apr '21

I'm looking at Bird's *Thinking Functionally with Haskell *and he gives two list comprehensions, asking under what conditions they deliver the same results [e | x <- xs, p x, y <- ys] [e | x <- xs, y <- ys, p x] First, I'm confused about what is the input and what is the predicate. The y <- ys in the first LC seems to be in a predicate position, and in the second it's a second input after x <- xs with p x in the predicate position . . . confusing me. The answer examples Bird gives are beyond me: They deliver the same result only if ys is a finite list: > [1 | x <- [1,3], even x, y <- undefined] [] > [1 | x <- [1,3], y <- undefined, even x] Exception: Prelude.undefined > [1 | x <- [1,3], y <- [1..], even x] {Interruped} I'm not sure what's being said here, or what points are being made.

2 4

Is map (map f) just map f?
by Galaxy Being 08 Apr '21

08 Apr '21

I'm in Bird's *Thinking Functionally with Haskell* and the topic is natural transformations. He says filter p . map f = map f . filter (p . f) and he has a proof, but one step of the proof he goes from filter p . map f = concat . map (map f) . map (test (p . f)) to filter p . map f = map f . concat . map (test (p . f)) which means concat . map (map f) => map f . concat which means map (map f) = map f ... or I'm getting this step wrong somehow. To begin with, I'm having a hard time comprehending map(map f), Any ideas on how this is possible? LB

3 3

Type class instance with Num
by Galaxy Being 04 Apr '21

04 Apr '21

I'm following LYHFGG and I have this class YesNo a where yesno :: a -> Bool instance YesNo Int where yesno 0 = False yesno _ = True but then I have to specify Int here > yesno (5 :: Int) True Just with 5 gives this error Ambiguous type variable ‘a0’ arising from the literal ‘5’ prevents the constraint ‘(Num a0)’ from being solved. Probable fix: use a type annotation to specify what ‘a0’ should be. I tried this instance YesNo (Num a) where yesno 0 = False yesno _ = True but got cryptic errors. What can I do to make yesno take any of Num's numbers? LB

2 1

Problem with Graphics.SOE
by Vitaly Dolgov 30 Mar '21

30 Mar '21

Hi, everybody! I'm trying to do an example from the book "The Haskell School of Expression", which originally uses `SOEGraphics`, I use `Graphics.SOE` instead, but I get the following error on each run: `user error (loadQueryFont)` I have no idea how to approach the problem... `:trace` outputs an empty exception :( Could you please help me to solve this? My environment is: Linux, ghc 8.10.4, HGL 3.2.3.2 The code is quite basic: ``` import Graphics.SOE main = runGraphics $ do w <- openWindow "Hello World!" (300, 300) drawInWindow w (text (100, 200) "Hello World!") k <- getKey w closeWindow w ``` Thank you, Vitaly

2 2