What if SELECT, FROM, WHERE were functions?

I've been looking into Prela the last few days and really like it :)

Conceptually, the two key operators `.select()` and `.and()` connect somewhat to the lineage of arrow notation [1], fork algebras [2], etc.

Left-to-right composition:

(>>>) :: (b -> c) -> (c -> d) -> (b -> d)

Fanout:

(&&&) :: (b -> c) -> (b -> d) -> (b -> (c, d))

The database-specific detail is enumerating the universe of entities to maintain shared correlations and using projections as ways to access information, so, in the above notation:

movie :: Movie -> Movie

title :: Movie -> String

movie >>> title :: Movie -> String

The specialization to then have Rust types be able to generate inlined query execution code at compile-time is quite neat. But, I wonder where the limitations of this approach are seen? In contrast to something like Soufflé which has a much more complicated optimizer but generates C++ code ultimately, it seems difficult to always rely on the Rust compiler. Likewise, some other projects like Crepe rely on Rust macros more heavily. And, the embeddability is a plus, but it does not look too easy currently to use from other languages as you would need to compile the query independently and provide something like an FFI wrapper.

Relatedly, some other posts about relational language design from the last couple days: https://news.ycombinator.com/item?id=49342530, https://news.ycombinator.com/item?id=49363617

And this tutorial looks interesting: https://northeastern-datalab.github.io/relational-language-t...

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[1] https://ghc.gitlab.haskell.org/ghc/doc/users_guide/exts/arro... [2] https://www.cosc.brocku.ca/Faculty/Winter/JoRMiCS/Vol1/PDF/v...