quasi-literal strawman

Ash Berlin ash_js at firemirror.com
Mon Dec 14 15:34:25 PST 2009

On 14 Dec 2009, at 22:44, Mike Samuel wrote:

> http://wiki.ecmascript.org/doku.php?id=strawman:quasis
> is a strawman for a concrete syntax that enables string interpolation
> as described in
> http://wiki.ecmascript.org/doku.php?id=strawman:string_interpolation .
> So far it's just an uploaded HTML file but I plan to make it more wiki friendly.
> If people want to edit it, let me know and I'll put out a wiki form pronto.

First things first: the string interpolation strawman[1] is not string interpolation. It's LINQ (Language Integrated Query) or very similar, which dare I say it, is what E4X is (or attempts to be, spec bug not withstanding) Which isn't to say I don't think the idea has merit, it is just more than simply string interpolation. (When i say its LINQ - it feels very much like the query syntax front end for it.)

The pessimist in my would like to point out that you could (and people inevitably will) still say `UPDATE foo SET x=$x`. Unless i've missed something crucial this doesn't protect against that (as its not  a sql`UPDATE ...`. Also which 'sql' - there are many variants)

backticks In perl, ruby and php is all the system execute command (which I suspect you know) but the "where it allows interpolation though with a more specific meaning than macro expansion" wording isn't quite correct -- it does more than just interpolattion.

I really like the idea of being able to do things like |var my regexp = re`(?i:\w+$foo\w+)`;|

quasi-strawman.html says:
>> It would be convenient for some DSL use cases to allow LineTerminators inside code, but it is unclear how this will interact with revision control systems that rewrite newlines on checkout

If you want to use a certain form of a new line for what ever reason, it would probably be best to use \n. Line continuations are rather annoying to use in practice - if you want the literal to be split over multiple lines, and to have new lines in the source you end up ending every line with \n\ which is just ugly. Since we are already talking about new syntax, I would vote for allowing multi-line literals.

If you haven't yet read http://www.python.org/dev/peps/pep-3101/ (Advanced String Formatting) I suggest you do - its well worth a read and feels like a possible very javascripty solution.

One thing I'm not seeing here is a way to interpolate one quasi literal inside another one. I'm guessing the intent is html`<h1>$x</h1>` would html escape the x variable (this wasn't actually explicitly stated anywhere that I read). But how do you say 'x is already html, don't escape it again?' I guess this comes down to how do you detect and interact with quasi-literals? Do they have a new typeof? What methods do the instances have? How exactly to you write new quasi tags/types?

I can understand not having printf style formatting codes, but how would you suggest you format a number to 2 decimal places?

In summary:
* Quasi-Literal or string interpolation strawman? whats what?
* How do you interact with literals (in more detail)
* What quasi types would be built in?
* I would *really* like multiline literals. (akin to pythons """ operator or heredocs in perl and ruby)
* The metadata example - there is no other mention to metadata
* I'm not sure its worth allowing such complex expressions inside the ${} (brackets example)
* No printf/formatting at all might be missed

Thanks for fleshing this out in more detail - I've been meaning to write an email about the lack of detail in the string interpolation strawman for a couple of weeks.


[1]: http://wiki.ecmascript.org/doku.php?id=strawman:string_interpolation

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