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Comment by panzi | Hacker News Reader

Indeed in some of the listed languages you can nest it like that, but in others (e.g. Python) you can't. I would guess they deliberately don't want to enable that and it's not a problem in their parser or something.

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As of python 3.6 you can nest fstrings. Not all formatters and highlighters have caught up, though.

Which is fun, because correct highlighting depends on language version. Haskell has similar problems where different compiler flags require different parsers. Close enough is sufficient for syntax highlighting, though.

Python is also a bit weird because it calls the format methods, so objects can intercept and react to the format specifiers in the f-string while being formatted.

I didn't mean nested f-strings. I mean this is a syntax error:

    >>> print(f"foo {"bar"}")
    SyntaxError: f-string: expecting '}'

Only this works:

    >>> print(f"foo {'bar'}")
    foo bar

You're using an old Python version. On recent versions, it's perfectly fine:

    Python 3.12.7 (main, Oct  3 2024, 15:15:22) [GCC 14.2.0] on linux
    Type "help", "copyright", "credits" or "license" for more information.
    >>> print(f"foo {"bar"}")
    foo bar

Even when nesting is disallowed, my point is that I find it preferable to not view it (and syntax-highlight it) as a “special string” with embedded magic, but as multiple string literals with just different delimiters that allow omitting the explicit concatenation operator, and normal expressions interspersed in between. I think it’s important to realize that it is really just very simple syntactic sugar for normal string concatenation.

While you're conceptually right, in practice I think it bears mentioning that in C# the two syntaxes compile differently. This is because C#’s target platform, the .NET Framework, has always had a function called `string.Format` that lets you write this:

  var str = string.Format("{0} is {1} years old.", name, age);

When interpolated strings were introduced later, it was natural to have them compile to this instead of concatenation.

There's no reason in principle why

    name + " is " + age + " years old."

couldn't compile to exactly the same. (Other than maybe `string.Format` having some additional customizable behavior, I don't know C# that well.)

Like python, and Rust with the format! macro (which doesn't even support arbitrary expressions), C# the full syntax for interpolated/formatted strings is this: {<interpolationExpression>[,<alignment>][:<formatString>]}, ie there is more going on then just a simple wrapper around concat or StringBuilder.

When not using the format specifiers or alignment it will indeed compile to just string.Concat (which is also what the + operator for strings compiles to). Similar to C compilers choosing to call pits instead of printf if there is nothing to be formatted.

If it’s treated strictly as simple concatenation syntactic sugar then you are allowing something like print(“foo { func() ); Which seems janky af.

> just very simple syntactic sugar for normal string concatenation.

Maybe. There’s also possibly a string conversion. It seems reasonable to want to disallow implicit string conversion in a concatenation operator context (especially if overloading +) while allowing it in the interpolation case.

I failed to mention the balancing requirement, that should of course remain. But it's an artificial requirement, so to speak, that is merely there to double-check the programmer's intent. The compiler/parser wouldn't actually care (unlike for an arithmetic expression with unbalanced parentheses, or scope blocks with unbalanced braces), the condition is only checked for the programmer's benefit.

> here’s also possibly a string conversion. It seems reasonable to want to disallow implicit string conversion in a concatenation operator context (especially if overloading +) while allowing it in the interpolation case.

Many languages have a string contenation operator that does implicit conversion to string, while still having a string interpolation syntax like the above. It's kind of my point that both are much more similar to each other than many people seem to realize.

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