BNFC
Access to AST nodes' positions in the input file
In order to be able to provide better error messages to the users, we would like to say
Error E occured on line 25, col 55
However, currently the positions of AST nodes in the input file are not accessible from AST. How could we access the nodes' positons? How do AST node positions relate to token positions e.g.,
position token PIdent (letter (letter|digit|’_’|’\’’)*) ;
I don't think that you can access the position of any node excepts token defined with the position keyword.
It could maybe be added as an option...
What we have to do currently, to address the issue is to introduce a bunch of internal constructions but these pollute our code badly....
in the original .cf file you'd have
Module. Module ::= [Declaration] ;
but we add
Module . Module ::= [Declaration];
internal PosModule . Module ::= Span [Declaration];
where the Span is a section of the input file, i.e., ( (x1, y1), (x2, y2) ):
Pos . Pos ::= Integer Integer ;
internal PosPos . Pos ::= Span Integer Integer ;
Span . Span ::= Pos Pos ;
internal PosSpan . Span ::= Span Pos Pos ;
The nasty consequence is that in all our functions which work with AST nodes, we always have to pattern match on the original constructors (Module) and the new ones with positions (PosModule).
It is a nasty hack that adds up a lot programming and maintenance cost.
What we could have is a function which computes a span from the position-tokens within it.
On Wed, Jun 12, 2013 at 10:59 PM, Michal Antkiewicz < [email protected]> wrote:
What we have to do currently, to address the issue is to introduce a bunch of internal constructions but these pollute our code badly....
in the original .cf file you'd have
Module. Module ::= [Declaration] ;
but we add
Module . Module ::= [Declaration]; internal PosModule . Module ::= Span [Declaration];
where the Span is a section of the input file, i.e., ( (x1, y1), (x2, y2) ):
Pos . Pos ::= Integer Integer ; internal PosPos . Pos ::= Span Integer Integer ; Span . Span ::= Pos Pos ; internal PosSpan . Span ::= Span Pos Pos ;
The nasty consequence is that in all our functions which work with AST nodes, we always have to pattern match on the original constructors ( Module) and the new ones with positions (PosModule).
It is a nasty hack that adds up a lot programming and maintenance cost.
— Reply to this email directly or view it on GitHubhttps://github.com/BNFC/bnfc/issues/28#issuecomment-19355141 .
We have forked bnfc and added some support (https://github.com/juodaspaulius/bnfc/). If there's interest we could guard these extension using a new command line parameter (e.g., --positions) and contribute back.