[Ur] Proposed location literals to track caller's location in error msgs.

Fri May 29 08:47:14 EDT 2015

El 28/05/15 a les 14:29, Adam Chlipala ha escrit:
> Why not just implement this functionality purely in the lexer, lexing
> the special marker as a string literal with the right contents?  You can
> call [ErrorMsg.spanOf] directly in the lexer, rather than via its alias
> [s] in the parser.

You are right, the simpler, the better.

Here is a possible code to add to urweb.lex, leaving urweb.grm untouched.

<INITIAL> "_LOC_" => (let val strLoc = ErrorMsg.spanToString 
(ErrorMsg.spanOf (pos yypos, pos yypos + size yytext))
                       in
                           Tokens.STRING (strLoc, pos yypos, pos yypos + 
size yytext)
                       end);

What do you prefer, the shorter _LOC_ or the PHP's style __LOC__ ?

-----------

Simple test sample:

---

fun myPartialListHd [a] (loc: string) (li: list a): a =
       case li of
         | h :: t => h
         | _ => error <xml>myPartialListHd: invalid arguments at {[loc]}
                      </xml>

fun main () : transaction page =
    let val res = myPartialListHd _LOC_ ([] : list int)
    in
       return <xml><body>result: {[res]}</body></xml>
    end