[Ur] Obtaining location information

[Sergey Mironov]

2015-03-16 3:29 GMT+03:00 Adam Chlipala <adamc at csail.mit.edu>:
> Let's see if I understand right: you want some token you can write in source
> code, to be replaced at compile time by the location of the token, along the
> lines of C's __FILE__ and __LINE__.

Yes, exactly!

> Yes, it sounds like an easy feature to add.  I would actually do it entirely
> in the parser.  I'd extend src/urweb.lex with a production for a new
> reserved identifier for this 'macro', and I'd extend one of the expression
> nonterminals in src/urweb.grm with a rule that translates the source
> location of said token into an Ur/Web string literal, using
> [ErrorMsg.spanToString], getting ahold of the span in the same way that it
> is already being produced to label each expression with its location for
> purposes of later error messages.

The only note from me: I plan to build source urls using the location
information, so it's better to have an access to line/character
position as integers. String representation would probably require
writing a parser  (which is still better than nothing, of cause!)