(Resending from right address) We're talking about *three* options: 1. syntax for pure Haskell values, which I'll call HSON (Haskell jSON). That's just an alternative to YAML/TOML/... That would need extensions to allow omitting optional fields entirely. 2. a pure Haskell embedded domain-specific language (EDSL) that simply generates cabal description records (GenericPackageDescription values). That would allow abstraction over some patterns but not much more. But that alone is already an argument for EDSLs—the one Harendra already presented. 3. a Haskell embedded domain-specific language (EDSL) designed for an extensible build tool, like Clojure's (apparently), SBT for Scala or many others. That would potentially be a rabbit hole leading to a rather *different* tool—with a different package format to boot. That can't work as long as all libraries have to be built using the same tool. But stack and cabal are really about how to manage package databases/GHC/external environments, while extensible build tools are about (a more powerful form) of writing custom setup scripts. I suspect some extensions might be easier if more of the actual building was done by the setup script, but I'm not sure. On 16 September 2016 at 10:57, yogsototh wrote:

...

I guess the overriding question I have here is: what is the PROBLEM being solved?

Let me share my experience with Clojure and lein. They use a clojure hash-map for their configuration. So yes arbitrary code could be executed and I believe this is a _very good thing_.

Why? Because it makes it very easy to add sub-configuration that can be used by third party plugin. For example:

- a plugin that help the use of environment variables (lein-environ) which is really helpful for application development (not so much for library development) - a plugin that use S3 for our private dependencies (not supported by default by lein)

For deployment: we were able to add request to our API server that provide not only the written version but also the git commit hash. So we could be certain of the version of the server. Too much time there were sys/admin deployment errors. And that could only be achieved because we were able to run arbitrary command in the project description file.

I certainly forget many other advantages of having a package description format which is simply a data structure in the hosted language. But this has by far my preference.

- cabal is ok, but very imperfect, I generally need to have a lot of copy/paste, I need to change it very often while writing application with many dependencies - JSON/YAML/TOML are simply not powerful enough to match all semantics we might need to configure a project. For example we might want to have Set instead of List for some properties. Or I don't know maybe ternary tree structures.

The point is: we pay a price by adding a step between the semantic and the syntax. While if our configuration format was in Haskell we could express the semantic more directly.

_______________________________________________ Haskell-community mailing list Haskell-community@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-community

-- Paolo G. Giarrusso - Ph.D. Student, Tübingen University http://ps.informatik.uni-tuebingen.de/team/giarrusso/