yesod-persistent VS parsec

I also looked into Snap (http://snapframework.com/) and Yesod (https://www.yesodweb.com/) for Haskell. I didn't really get anywhere with those though because I had build issues with dependencies and was in a bit of a hurry so I put them off for later.

If you have a yesod app and want to try this out, I've got a cabal.project that works for yesod and persistent: https://github.com/yesodweb/yesod/pull/1769

It would be an unorthodox choice. If you're looking to use this personal site as a portfolio project, you'd probably be better off using something like Node (JS), Java, or Python which tend to be a bit more marketable. However, if you want to try learning Haskell, then building a personal site with it seems like a great way to dive in. If you want to learn a bit more, Yesod seems to be the most well-documented Haskell web framework

I believe yesod is the go-to all encompassing framework.

frameworks like yesod and IHP

In this blog post I’m presenting an implementation of a Wiki System in the spirit of the legendary C2-Wiki - written in Haskell with the Yesod framework.

I'm wondering if this is related to this.

> Every language phasing the web is stringly typed

Heh, not even close. Off the top of my head I can think of Ur/Web as an extreme example ( http://www.impredicative.com/ur ), and slightly more mainstream systems like Yesod ( https://www.yesodweb.com ). I've worked professionally with Haskell, although not for Web stuff. These days I mostly work with Scala, which has a similar typing mindset to ML/Haskell, but unfortunately inherits a lot of stringly typed legacy from Java. We use an in-house library that provides zero-cost newtypes to distinguish between different semantically-distinct data types, many of which just-so-happen to be representable as subsets of String (e.g. GET parameter names, GET parameter values, POST bodies, etc.). This makes it a type error to try and e.g. concatenate different sorts of data together.

W.r.t. "escaping", I tend to avoid it entirely since it's inherently unsafe:

- "Escaping" doesn't distinguish between its input and output types; they're both just "String", and we have to make assumptions about the contents of each (i.e. it's unsafe)

- Having the same input and output types makes it possible to "double-escape" by accident. This discourages the use of escaping, just-in-case it happens to be done elsewhere; hence it's very common to end up without any escaping taking place.

- Having the same input and output types makes escaping functionally unnecessary: anything we do to an escaped string could also be done to an unescaped string, so it's up to us to remember that it's needed (i.e. it's unsafe).

The whole idea of "escaping a string" betrays a flawed approach to the problem. Instead of throwing everything into the same representation, then manually trying to figure out whether or not a value comes from a particular subset of that representation or not, it's much easier and safer to avoid lumping them all together in the first place. If our inputs have a certain type (e.g. HTTP.Get.Val) and we can only output certain other types (e.g. JSON, Map[HTTP.Header.Key, HTTP.Header.Val], etc.), then the processing which turns input into output is forced to specify any necessary conversions. Whilst such conversions may involve escape sequences, having them associated to particular types is more akin to serialisation.

Heck, at my first PHP job we largely solved this problem not by 'filtering and escaping', but by modifying the PHP interpreter to distinguish between 'clean' and 'dirty' strings (with literals being clean, and $_GET, etc. being dirty). Operations like concatenation would propagate 'dirtiness', and output functions like 'echo' would crash if given a dirty string. Traditional 'escaping' functions would convert dirty strings to clean ones, and crash when given a clean string. Having this be dynamic was more annoying than ahead-of-time compile errors, but it still did a pretty good job.

There's pretty much no excuse for stringly typed languages/libraries/etc. when such such trivial solutions exist, other than the historical inertia of legacy systems.

The project is going to make use of Warp. To smoothen the development process I set up yesod-bin according to their template for non-yesod projects. This worked fine initially, giving me hot reloading on file changes, but after adding the private package as described above it's giving the following error:

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.