Linq and Learning to Be Declarative

It really isn't. The benefit of pure all the way down is that later you can replace bits with something more performant if necessary. But starting out with the idea that some bits should never be pure just means none of it is. The beauty of pure functional programming is that its very compositional nature means that you can replace a component without having a detrimental effect to everything its composed with: as long as you maintain referential transparency for that component.

What we gain from imposing the pure functional constraints on ourselves is genuine composition. If we compose two pure functions into a new function, that resulting function will also be pure. This is the pure functional programming super power that leads to fewer bugs, easier refactoring, easier optimisation, faster feature addition, improved code clarity, parallelisation for free, and reduced cognitive load. Opting out for arbitrary reasons at certain stages of the vertical threatens all of that.

Here's things Clojure, for example, offers:

1. Structural sharing which makes you less likely to have to dig in to procedural code.

2. The transient function which takes an immutable data structure and makes it... not immutable... you can now do your procedural code, then switch back into immutability land with persistent!.

3. If the above fails, you can dip into Java.

So yeah, I vehemently disagree with C# being the best. I could kinda see it if you said F# (type safety), but C# itself? Uhhh.

I really love C# but I will also say that 100% purity is a super power that C# will never have (can't have 'em all).

What's important to me is that I can understand the intent of the code, that I can reason about how that code will be executed at runtime, and that I can easily debug the code if needed.

Of course, there's no need to go full enterprise Java. Never go full enterprise Java.

But having ten lines of clear code that's easily debuggable and which runtime characteristics is predictable is much better than one dense line that's difficult to untangle, or a few that's hard to predict what will do etc.

So from an API perspective, I think returning IEnumerables can end up being too cute. The caller has to deal with this unknown thing.

In general you should be clear about what you return and loose about what you accept. If your whole API is returning IEnumerables and some are expensive to iterate and others are not its actually less clear what I'm getting. And this isn't to say List is always the answer either.

Cases where it isn't:

- risk of multiple execution (there is a CA warning for this)

- when returning data protected by a mutex, you should always materialize a copy of the returned list/array rather than return an enumerable

These patterns are commonplace for many years now in many languages.

The intention was to show how declarative code can come from imperative with a 'true' one-liner.

Or are you suggesting that the majority of programmers struggle to read and understand fluent method chaining?

I don’t have a dog in this fight because this blog post is very novice oriented. I’m just genuinely confused why you think it’s unreadable or “clunky”. What is it about the fluent example that you find clunky?

Writing your own LINQ provider is a very niche activity done by people who want to translate or “transpile” C# expression trees into something else.

It is fundamentally a difficult endeavor because you’re trying to construct a mapping between two languages AND you’re trying to do it in a way that produces efficient target code/query AND you’re trying to do that in a way that has reasonable runtime efficiency.

Granted, on top of that, I’m sure LINQ provider SDKs probably add their own complexity, but this isn’t an activity that C# developers typically encourage.

Also adjacently worth mentioning that I tend to use Dapper instead of EF, so there's even less use of this type of expression all around unless it's actual SQL or assembled SQL via a query builder.

I love Python, its my main daily driver, both at work and by preference for most of my personal coding, but Python comprehensions and genexps are much more limited than LINQ language level query syntax (Scala’s visually-similar construct is more like LINQ in capabilities) and Python—purely because of core and stdlib convention which also drive convention for the ecosystem, not actual structural features—lacks anything like the method syntax as a common API (unlike, say, Ruby).

EDIT: Thinking about it a little bit, though, it should be possible in theory to implement LINQ in Python without language level changes (including providing something close to but not quite as clean as the language level query syntax[0]) as a library via creative use of inspect.getsource and ast.parse, both for providing the query syntax and for building the underlying expression tree functionality around which providers are built (support for future python versions would require implementing translation layers for the ASTs and rejecting unsupported new constructs). Conceptually, this is similar to how a lot of embedded DSLs in Python for numeric JIT, compiling GPU kernels, etc., from (subsets of) normal Python coded are done.

[0] existing comprehension/genexp syntax looks similar, but relies on simple iteration, not pushing code execution out to a provider which may be doing something very different behind the scenes, like mapping "if..." clauses into SQL WHERE clauses for a database query.