Rio: Web apps in pure Python

I'm not trying to put words in his mouth (I'm pretty sure I delineated his direct quotes with quotation marks). But I saw him write multiple paragraphs about the complexity of lexing multi-statement lambdas in Python due to its whitespace sensitivity, and then conclude that the user facing interface must necessarily be complex too, which just feels fallacious to me. If the complexity of the implementation doesn't factor into the design then why go through so much effort to communicate how difficult it is to lex? He compares the implementation to a "2000 step [...] infinite-dimensional" mathematical proof.

I just fundamentally don't buy the argument that one statement in a lambda is fine, but two is dark magic that needs to be removed from the call site and quarantined in a separate def, and I think if the implementation were simpler GVR wouldn't have been so diametrically opposed to the feature. Even if he outsourced the "puzzle solving" to an external contributor, no one enjoys the increased maintenance burden of a complex implementation.

Anyone who's ever written customer facing code knows what it's like to receive a seemingly simple feature request that's actually difficult to implement because of prior architectural decisions, and the "gut reaction" is to convince the user that the feature itself is bad. I hate to invoke comedy but this reminds me of the microservices meme: https://www.youtube.com/watch?v=y8OnoxKotPQ

It's a jab towards mathematicians in the context of criticizing a language proposal. He's comparing the complexity of mathematicians and their 2000 line proofs to the complexity of allowing statements in lambdas. He explicitly calls the proposal a "Rube Goldberg contraption".

> Bit of correction: no statements and a single - arbitrarily complex - expression.

I phrased it as a dichotomy between single and multiple statements because in many languages there's the concept of an 'ExpressionStatement', which is a single expression that acts as a statement. This makes the boundaries between a single statement and an expression somewhat murky. In JS for example the MDN docs have this to say about ExpressionStatements: "Apart from the dedicated statement syntaxes, you can also use almost any expression as a statement on its own." [1] GVR himself calls it "the problem of the multi-statement lambda" rather than "the problem of the statement lambda".

I don't want to get bogged down in pedantic debates about terminology though. I completely understand how it works, and said in my very first reply to you: "but it's nice to not be limited to expressions".

> End of the day, support for statements in a lambda would lead to a need for new symbols.

All it would require is a newline character. He calls this out in the blog post: "If the double colon is unpythonic, perhaps a solution could be found that uses a single colon and is still backwards compatible [...] I actually have one in mind: if there's text after the colon, it's a backwards-compatible expression lambda; if there's a newline, it's a multi-line lambda; the rest of the proposal can remain unchanged. Presto, QED, voila, etcetera."

There's absolutely nothing complex about allowing statements in lambdas from a user interface perspective (all of the complexity is in the implementation). Almost every modern language has support for this feature. Even Golang, which is perhaps the epitome of simplicity — the language that fought tooth and nail against generics, and doesn't have a ternary operator (or inline if), or string interpolation — supports defining inline callback functions with statements. There are even whitespace sensitive languages like CoffeeScript that bit the bullet and don't impose any restrictions on lambdas. The simplicity argument just feels really weak to me. At the time that blog post was written a Python user couldn't add a print statement to a lambda to debug their code. How in the world is that simple for biology students and people writing one-off projects?

[1] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...

I've seen way more bloated React/Angular SPA apps than the typical PHP/jQuery Web 2.0 from back in the day.