PEP 750: Tag Strings for Writing Domain-Specific Languages

Post by RhysU » Sun, Aug 11, 2024, 8:27 PM UTC

pauleveritt wrote: post #90

RhysU wrote: post #87

Earlier quoted context omitted.

Why could you not know these things without a language feature? > ...other stuff that happens before evaluation... A greet(string) function could parse the string and resolve the names itself: parsed = parser(string) resolved = resolver(parsed) return formatter(resolved) If you hate boilerplate, make the first two steps into a decorator. A PEP introducing a grand unified theory of magic (tag strings) isn't inherently…

If the string is an f-string, it is immediately evaluated and you no longer have access to the interpolation info for a resolver. If the string is not an f-string, you get no help from Python tooling. In both cases, you have to use frame hacks to get back to the scope, which has negative consequences.

Post by ianbicking » Mon, Aug 12, 2024, 5:13 AM UTC

pauleveritt wrote: post #84

ianbicking wrote: post #29

I LOVE tagged templates in JavaScript. But in Python I could also imagine YET ANOTHER constant prefix, like t"", that returns a "template" object of some sort, and then you could do html(t"") or whatever. That is, it would be just like f"" but return an object and not a string so you could get at the underlying values. Like in JavaScript the ability to see the original backslash escaping would be nice, and as an impr…

Cool to see you jump in, Ian. I don't particularly mind the prefix thing. It came up in the PEP discussion, as did choice of backticks to indicate this is different. But JS template literals -> tagged template literals shows, you can get from A to B without a fundamental change. I'm very interested though in the deferred part. I agree that there is complexity. I weigh that, though, against the complexity of existing…

    return 
      {items.map((item, i) => {item})}
    ;

    exec(sql`
      SELECT * FROM a_table
      WHERE category = ${category}
        ${subcategory ? sql`AND subcategory=${subcategory}` : sql``}
    `)

Post by prpl » Wed, Aug 14, 2024, 6:45 PM UTC

pauleveritt wrote: post #82

throwitaway1123 wrote: post #46

Earlier quoted context omitted.

For a practical example of this technique used in JS take a look at libraries like htm and lit-html: https://github.com/developit/htm

(PEP co-author here) The htm folks did a Python implementation: https://pypi.org/project/htm/ It required a janky workaround for the absence of this PEP: https://pypi.org/project/tagged/ I used these to investigate ideas about component-driven development: https://viewdom.readthedocs.io/en/latest/

Post by jimbaker » Sat, Aug 17, 2024, 5:41 AM UTC

masklinn wrote: post #20

formerly_proven wrote: post #2

Yikes. Don't get me wrong, I totally understand the reasoning why this would be useful (though I violently disagree with the idea of deferring the evaluation of the contained expressions), but it's also so very kitchensinky and adds so little over just calling a function (which doesn't require a 20-page explainer, as everyone already knows how function calls work). It also promotes using what looks like string interp…

> This seems really awkward to me for building stuff like the suggested use cases of XML/HTML or SQL templating. Compared to what? At the end of the day you're still doing string formatting, if you want parsing, then you'd feed the item into a parser, which this doesn't preclude. The interface sounds a lot better than JS's anyway, as that completely separates the literal strings and the interpolations so you have to…

Post by jimbaker » Sat, Aug 17, 2024, 6:02 AM UTC

Groxx wrote: post #56

... is this any different than a function like this: greet("hello {world}") which walks the call stack to find the variables, and uses them as locals / arguments? If so: why not just do that? I would expect the performance to be kinda terrible compared to a language-intrinsic, but this hardly seems like a thing worth truly optimizing. And if it's too costly at runtime, someone can implement a parse-time AST rewriter,…