BenHanson/gram_grep

Error recovery is missing

mingodad opened this issue · 9 comments

mingodad commented

While converting some grammars I noticed that the error for error recovering is not implemented.

Example grammar using error recovery that works with bison:

%nonassoc error
%left '(' ')'
%left '+' '-'
%left '*' '/'
%nonassoc integer

%%

stmts:
	stmts stmt
	| stmt
	| %prec '('
	;

stmt:
	expr ';'
	| error ';'
	;

expr:
	expr '+' expr
	| expr '-' expr
	| expr '*' expr
	| expr '/' expr
	| expr error expr
	| '(' expr ')'
	| integer
	;

%%

//[0-9]+	integer
BenHanson commented

Yes, I'm not intending to implement this feature.

Also if you try to use a huge grammar with parsertl generally it will likely struggle. Ideally I would use bison style table compression (making sure to dodge the GPL mind you), but getting this far was enough of a struggle I have to admit!

mingodad commented

And what about byacc https://github.com/ThomasDickey/byacc-snapshots:
Bison generating postgresql-16:

/usr/bin/time bison-nb postgresql16b2-naked.y
1.36user 0.03system 0:01.37elapsed 101%CPU (0avgtext+0avgdata 17204maxresident)k
0inputs+4072outputs (0major+10888minor)pagefaults 0swaps

/usr/bin/time byacc-nb postgresql16b2-naked.y
1.59user 0.02system 0:01.61elapsed 99%CPU (0avgtext+0avgdata 42124maxresident)k
0inputs+6800outputs (0major+10631minor)pagefaults 0swaps
mingodad commented

Here is the postgresql-16 naked grammar:
postgresql16b2-naked.y.zip

mingodad commented

It seems that even lemon struggles with postgresl-16:

/usr/bin/time lemon-nb -s postgresql16b2-naked.lemon
Parser statistics:
  terminal symbols...................   522
  non-terminal symbols...............   706
  total symbols......................  1228
  rules..............................  3293
  states.............................  3490
  conflicts..........................     0
  action table entries............... 129153
  lookahead table entries............ 129174
  total table size (bytes)........... 546522
15.43user 0.25system 0:15.81elapsed 99%CPU (0avgtext+0avgdata 422128maxresident)k
0inputs+123656outputs (0major+105236minor)pagefaults 0swaps

postgresql16b2-naked.lemon.zip

BenHanson commented

And what about byacc https://github.com/ThomasDickey/byacc-snapshots

That actually looks really interesting.

mingodad commented

I have a fork here https://github.com/mingodad/lalr-parser-test with some cosmetic changes.

BenHanson commented

After seeing Charles Baker's description of supporting "error", I might have a look at this at some point.

mingodad commented

That would be a nice addition !
Also instead of reporting errors one by one, probably trying to recover and going forward and showing the accumulated errors would be nice.
Another interesting error recovering and messaging is done here https://github.com/sqmedeiros/lpeglabel#relabel-syntax .