Difference between revisions of "User:Mlforcada/Robust LR for Transfer"

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(Created page with "We need a way to implement Apertium4 Bison grammars that are robust. Here, '''Bison GRAMMAR''' is a LALR(1) grammar with actions between braces. There should be a way (or a ...")
 
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One possible way to do so is to model left-to-right '''restarts''' as follows:
 
One possible way to do so is to model left-to-right '''restarts''' as follows:
   
* by accepting the longest possible constituent that cannot be merged with the remaining output and generating some kind of translation for it
+
* by accepting the longest possible constituent (in the original grammar <math>G</math> that cannot be merged with the remaining output and generating some kind of translation for it
* and treating the remaining output as a complete sentence again
+
* and treating the remaining output as a complete sentence again
  +
  +
For instance, if the grammar <math>G</math> is:
  +
<pre>
  +
S : NP VP { write(agree(nom($1),$2)) };
  +
NP : n { write($1) } ;
  +
VP : v { write($1) } ;
  +
| v NP { write(acc($2),$1) };
  +
</pre>
  +
the sequence <math>v n n</math> could not be parsed and would lead to an error. However, it could be seen as a NP followed by a VP, and a translation could be generated for both. One could augment the grammar by adding some rules:
  +
<pre>
  +
S : NP VP { write(agree(nom($1),$2)) }
  +
| NP TryS { write($1); write($2) } # translate an NP and skip
  +
| VP TryS { write($1); write($2) } # translate a VP and skip
  +
;
  +
TryS : S { write($1); }
  +
| ; # the remaining part may be empty
  +
NP : n { write($1) } ;
  +
VP : v { write($1) } ;
  +
| v NP { write(acc($2),$1) };
  +
</pre>

Revision as of 16:42, 1 January 2015

We need a way to implement Apertium4 Bison grammars that are robust.

Here, Bison GRAMMAR is a LALR(1) grammar with actions between braces.

There should be a way (or a procedure) to complete handwritten rules, if possible automatically, to generate a robust parser (and translator). The idea is to take the handwritten Bison grammar and complement it with automatically-generated glue rules in such a way that conflicts are not produced (or are harmless) to produce a new grammar .

One possible way to do so is to model left-to-right restarts as follows:

  • by accepting the longest possible constituent (in the original grammar that cannot be merged with the remaining output and generating some kind of translation for it
  • and treating the remaining output as a complete sentence again

For instance, if the grammar is:

S : NP VP  { write(agree(nom($1),$2)) };
NP : n   { write($1) } ;
VP : v  { write($1) } ;
   | v NP  { write(acc($2),$1) };

the sequence could not be parsed and would lead to an error. However, it could be seen as a NP followed by a VP, and a translation could be generated for both. One could augment the grammar by adding some rules:

S : NP VP  { write(agree(nom($1),$2)) }
  | NP TryS { write($1); write($2) }      # translate an NP and skip
  | VP TryS { write($1); write($2) }      # translate a VP and skip
  ;
TryS : S  { write($1); }
     | ;                                  # the remaining part may be empty
NP : n   { write($1) } ;
VP : v  { write($1) } ;
   | v NP  { write(acc($2),$1) };