stackage VS parsec

Writing Haskell programs that rely on third-party packages is still an issue when it’s a not actively maintained package. They get out of date with the base library (Haskell’s standard library), and you might see yourself in a situation where you need to downgrade to an older version. This is not exclusive to Haskell, but it happens more often than I’d like to assume. However, if you only rely on known well-maintained libraries/frameworks such as Aeson, Squeleto, Yesod, and Parsec, to name a few, it’s unlikely you will face troubles at all, you just need to be more mindful of what you add as a dependency. There’s stackage.org now, a repository that works with Stack, providing a set of packages that are proven to work well together and help us to have reproducible builds in a more manageable way—not the solution for all the cases but it’s good to have it as an option.

> That is fine, as far as it goes, but obviously this will, at some point, be at odds with the interests of programmers looking to use Haskell as a practical, stable tool.

That's what Stackage is.

Stackage provides consistent sets of Haskell packages, known to build together and pass their tests before becoming Stackage Nightly snapshots and LTS (Long Term Support) releases. [1]

Java will never get this.

[1] https://www.stackage.org/

makefile_dir := $(dir $(abspath $(lastword $(MAKEFILE_LIST)))) export PATH := $(makefile_dir):$(PATH) project_name ?= project_main ?= src/.hs retag_file ?= $(project_main) stack.yaml: @test -f stack.yaml || (echo -e "This makefile requires a 'stack.yaml' for your project.\nYou don't need to use 'stack' to build your project.\nYou just need a 'stack.yaml' specifying a resolver compatible with your GHC version.\nSee https://www.stackage.org/" && exit 1) stack: stack.yaml @which stack || (echo -e "This makefile requires 'stack' to be on your path. Use GHCup to install it.\nSee https://www.haskell.org/ghcup/" && exit 1) .PHONY: stack warning.txt: -@uname -a | grep -q Darwin && echo "WARNING: On Mac, you must alias 'make' to 'gmake' in your shell config file (e.g. ~/.bashrc or ~/.zshrc). Symbolic links will not work." | tee warning.txt @echo "Add 'warning.txt' to your .gitignore file if you never want to see this message again." hasktags: warning.txt stack @echo 'stack exec -- hasktags' > hasktags @chmod +x hasktags @echo "You might like to add 'hasktags' to your .gitignore file." format: stack @stack exec -- fourmolu --stdin-input-file $(project_main) .PHONY: format retag: warning.txt stack @stack exec -- haskdogs -i $(retag_file) --hasktags-args "-x -c -a" | sort -u -o tags tags .PHONY: retag tags: warning.txt hasktags stack @stack exec -- haskdogs .PHONY: tags ghcid: stack @stack exec -- ghcid \ --command 'stack repl --ghc-options "-fno-code -fno-break-on-exception -fno-break-on-error -v1 -ferror-spans -j"' \ --restart stack.yaml \ --restart $(project_name).cabal \ --warnings \ --outputfile ./ghcid.txt .PHONY: ghcid

(why lts-18.28? it's the latest 8.10 release on https://www.stackage.org/ )

I don't see way community maintenance can change the GHC for nightly.

It makes total sense that it fails since at no point I requested that the library be installed, which makes me wonder: Is there any way to request Hackage to install SDL and GLEW before attempting the build? I see Stackage has debian-bootstrap.sh. Does something similar exist for Hackage?

At this point, you can try a Stack snapshot that uses an older version of GHC. Looking at Stackage, you can see that the latest version before 8.10.* is 8.8.4 (using LTS 16.31). Starting over with that snapshot, you find that the packages that you need are in the snapshot and work.

On the contrary, I think this is standard practice for packages which are part of stackage. When stackage nightly switches to a new version of ghc, all the packages which are incompatible with the new ghc are dropped from nightly. My understanding is that maintainers are then expected to fix their packages, at which point more and more packages are included in the nightly snapshot. The next lts to include that version of ghc is only released later, once most packages have been added back, so unlike ghc users who diligently upgrade to the latest ghc, stackage users who diligently upgrade the latest lts snapshot shouldn't see a big drop in the number of compatible packages.

I found the latest stack lts version, and it's associated ghc version here: https://www.stackage.org/

Writing Haskell programs that rely on third-party packages is still an issue when it’s a not actively maintained package. They get out of date with the base library (Haskell’s standard library), and you might see yourself in a situation where you need to downgrade to an older version. This is not exclusive to Haskell, but it happens more often than I’d like to assume. However, if you only rely on known well-maintained libraries/frameworks such as Aeson, Squeleto, Yesod, and Parsec, to name a few, it’s unlikely you will face troubles at all, you just need to be more mindful of what you add as a dependency. There’s stackage.org now, a repository that works with Stack, providing a set of packages that are proven to work well together and help us to have reproducible builds in a more manageable way—not the solution for all the cases but it’s good to have it as an option.

The Parsec library for Haskell uses combinators, and there are a few good resources around the internet which explore it, if you know Haskell.

Parse the expression using parsec library ( if you're unfamiliar with it please check out https://hackage.haskell.org/package/parsec) it's a strong library for parer combinators. Once you parse the expression u need to define and sum up the similar terms. Check this example out - https://fpunfold.com/2020/05/18/making-a-calculator-in-haskell-with-parsec.html

Konbini is a functional parser combinator library inspired by Haskell parsing libraries like Parsec. It's (hopefully) fairly easy to use, and is about as performant as the better-parse library. In fact, it's quite similar to better-parse in many aspects. The main difference is in how parsers are composed. Where better-parse prefers operators and infix functions, Konbini instead uses plain functions.

Hi everyone, I'm learning F# and currently trying to do a Parsec-like CE, just to get comfortable with computation expressions.

good libraries for parsing: parsec, attoparsec etc.

Thank you! When I read the title I only knew about https://hackage.haskell.org/package/parsec, and for a moment I was very confused…

The more "idiomatic" way would be to use a parser library, e.g. parsec, attoparsec, or megaparsec. But even then I think it would be a lot easier to maintain if you could preserve the angle brackets <> in the input.