Interactive toplevel parsing

May 31, 2012 at 1:49 PM

Hi,

I was wondering if it is possible to use GPPG in an Interactive toplevel enviroment.

If yes are there any example or any guidelines to follow?

Coordinator
Jun 6, 2012 at 10:10 AM

Hi baucez.  Well, gppg parsers can work with any scanner, interactive or not.  However building interactive *scanners* is sometimes tricky.

If you have an incremental scanner, one that returns symbols as they are typed in, then the parser may behave a little unexpectedly.

gppg parsers can sometimes make a parsing decision without needing a lookahead symbol, but in other circumstances will not make a move until it has seen the next symbol.  This sometimes appears a little odd.

Writing interactive scanners is likewise tricky, because a scanner needs one character of lookahead before it can declare that it has recognized *any* regular expression. For example if you have a C# scanner that has just read f,o,r, then it cannot return the token "keyword-for" without checking if the following characters are "each".  Usually it can work if input is read line-by-line and no regular expression contains a line-separator.

Other than this I can't give any general guidelines.

Cheers

John