starlark VS dhall

— a in b not in c

WalterBright mentioned that D will give you an error. When designing Starlark (a derivative of Python), I also decided to give an error for this, by making the comparison operators non associative.

https://github.com/bazelbuild/starlark/blob/master/design.md...

I agree this Python feature can look cute, but I've found it's rarely useful and can easily be avoided.

Having done some nontrivial Bazel/Starlark hacking, I completely agree that lightweight static types would be a good usability improvement. But I want to point out that Starlark is actually not Turing complete, which is imo one of the more interesting characteristics it has. Recursion is forbidden (https://github.com/bazelbuild/starlark/blob/master/spec.md#f...) and loops must be structural; there is no while loop or other unbounded iteration construct. Starlark is one of the more capable and mainstream non-Turing-complete languages out there, and doesn't resemble the other common ones which mostly show up in theorem provers. On the one hand I think the logic in a build system that needs to reason about incremental builds absolutely should be guaranteed to terminate, but in some particularly painful situations I've had to resort to iteration over smart-contract-style "gas" parameters.

The implementations and users page mentioned above:

https://github.com/bazelbuild/starlark/blob/master/users.md

Starlark: Starlark is a language for describing build transformations, inspired by Python, but with features that make it suitable for embedding in software like Bazel. It can be used for configuration generation due to its capability for deterministic evaluation and expressing complex build transformations.

In the design of Starlark (https://github.com/bazelbuild/starlark), I often had to push back against new feature requests to keep the language simple. I explicitly listed simplicity as a design goal.i

Of course, the scope of the language is not the same as general purpose languages, but there's always pressure from the users to add more things. I also think many people underestimate the cost of adding new features: it's not just about adding the code in every compiler/interpreter, specifying every edge-case in a spec, updating all the tooling for the language and writing tutorials; it's also a cost on everyone who will have to read any of the code.

one of the benefits of starlark (unlike python): "Starlark is suitable for use in highly parallel applications. An application may invoke the Starlark interpreter concurrently from many threads, without the possibility of a data race, because shared data structures become immutable due to freezing." from https://github.com/bazelbuild/starlark/blob/master/spec.md - it's not python, you can't do recursion (!) and it's more limited (you can't read a file in bazel, and parse it, you have to make this operation into the graph somehow)

You can do the same in Bazel which uses Starlark for its BUILD files. Starlark is a dialect of Python so it makes it super easy to work with.

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If you mean installing Dhall's dependencies (https://github.com/dhall-lang/dhall-haskell/blob/master/dhal...), those aren't too crazy, but they're definitely not all "beginner level". Template Haskell in particular is quite heavyweight.

Ok, lets be specific. Lets write a comment to explain this function:

https://github.com/dhall-lang/dhall-haskell/blob/master/dhal...

I haven't tried it but apparently you can compile to Nix from Dhall:

> You can use this compiler to program Nix using the Dhall language. This package targets people who wish Nix had a type system.

https://github.com/dhall-lang/dhall-haskell/tree/master/dhal...

If the problem is the syntax and people wants some other format that compiles to nix, there's dhall

https://dhall-lang.org/

https://github.com/dhall-lang/dhall-haskell/tree/master/dhal...

https://www.haskellforall.com/2017/01/typed-nix-programming-...

Dhall is a generic config language with some programming capabilities (but not turing complete) that can compile to json, yaml, and other formats, like in this instance nix.

For my GSoC project, I built from scratch the dhall-csv package on the Dhall Haskell implementation Github Repository. Said package provides two executables, dhall-to-csv (which converts Dhall files into CSV files) and csv-to-dhall (which converts CSV files into Dhall files). It also provides Haskell libraries with the functions that translate bidirectionally between Dhall and CSV.

> If you add constraints (like not being able to feed the program to itself as is done in the halting problem and not allowing unbounded loops) then it is possible to determine if a program will terminate or not.

Dhall is a good example - https://github.com/dhall-lang/dhall-haskell .

See also https://dhall-lang.org/

That just seems like an even greater nightmare to me. Soon you would have to learn to read and understand a custom program in a Turing-complete language for each and every installation.

The proper solution is a DSL, just a better DSl. Or perhaps a DSL embedded in something like dhall <https://dhall-lang.org/>, but definitely not a general-purpose programming language.

Dhall