I've been experimenting with various possible syntaxes for <*...*> in the ANTLR grammar, here are my current thoughts (I'd like some feedback).
I had proposed in 2012-09-02 (http://www.mail-archive.com/readable-discuss@lists.sourceforge.net/msg00806.html) that they have this semantic: "<* ... *>" are like ( ... ) in that they surround a list, but they do NOT turn off indentation processing. A "<*" resets the "indent" level to a 0-length string, skips all horizontal whitespace, and then restarts reading an expression with indentation processing still live. A blank line inside <* ... *> ends an expression WITHIN the <* ... *>, but stays within <* ... *>; only eof or active *> can close the <*. Once all that mapping is done, the range of <* ... *> is replaced with the mapped result. But these semantics for <* ... *> that I had originally proposed turn out to be subtly tricky to do. Indented expressions (i_expr) "expect" to be terminated by end-of-line. Terminating them also with "*>" the "obvious" way means I have to insert empty alternatives everywhere, which creates a bunch of ambiguities. I can allow empty matches & force "greedy" matching everywhere, but that is complex and also turns off lots of checks I'd rather not disable. Especially because it also makes the grammar much more complex, increasing the likelihood of errors. In addition, doing this might make it harder for some people to implement. That level of global complication seems unwarranted; we want simple, not complicated. But I think that's completely unnecessary. Basically, <* ... *> is supposed to create a list but yet keep indentation processing enabled, and I think there are two easily-distinguished use cases: 1. Multi-line case, e.g., so that blank line doesn't end all expressions. This basically keeps things from marching to the right-hand-side forever, and is useful for things like library definitions, where you want blank line to not end the *entire* expression. It's easy to require that, in this case, "<*" must be followed by an end-of-line. 2. "All on one line" - the <*...*> is on one line, e.g., one-variable let: let <* x cos(0) *> In this case, we could require that "<*" and spaces be followed by a (one-line) "head" production; by only using "head" we eliminate the ambiguities that hit the "obvious" approach. If we do this, we might need to move "$" processing into the "head" production so "$" can be used inside the <* ... *>, and forbid the use of "$ at the end of a line", but I don't see a real need for that particular rule. --- David A. Wheeler ------------------------------------------------------------------------------ Master Visual Studio, SharePoint, SQL, ASP.NET, C# 2012, HTML5, CSS, MVC, Windows 8 Apps, JavaScript and much more. Keep your skills current with LearnDevNow - 3,200 step-by-step video tutorials by Microsoft MVPs and experts. ON SALE this month only -- learn more at: http://p.sf.net/sfu/learnmore_123012 _______________________________________________ Readable-discuss mailing list Readable-discuss@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/readable-discuss
