Implementing "%fallback" like in Lemon parser

[Domingo Alvarez Duarte]

I've been adding grammars to 
https://mingodad.github.io/parsertl-playground/playground/ an "Yacc/Lex" 
compatible wasm/online editor/tester and for grammars with big number of 
soft keywords like PostgreSQL, Vitess, ... the resources usage in terms 
of memory/time/size for the parser grows exponentially proportional to 
the number of such tokens.

The Lemon parser generator has an option "%fallback" (see 
https://sqlite.org/src/doc/trunk/doc/lemon.html#pfallback ) that reduce 
the resources usage and also has less probabilities of generating conflicts.

I've implemented it on 
https://mingodad.github.io/parsertl-playground/playground/ and I've got 
good performance gains:

Statistics of Vitess SQL parser (be patient)(partially working):
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build master parser -> Time taken : 87ms
parse user grammar -> Time taken : 5ms
start build user grammar -> Time taken : 2ms
build user parser -> Time taken : 1481ms
dump input parser tree -> Time taken : 10ms
====

Statistics of Vitess SQL parser with fallback (partially working):
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build master parser -> Time taken : 34ms
parse user grammar -> Time taken : 3ms
start build user grammar -> Time taken : 0ms
build user parser -> Time taken : 446ms
dump input parser tree -> Time taken : 5ms

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Would be nice to have the same implemented in bison.

What is the opinion of people on this list ?

Cheers !