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Justfy that LALR parsers are faster than LR parsers?

Updated: 8/16/2019
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14y ago

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LALR parsers have an equal number of states as an LR(0) parser. LR(1) parsers have a number of states dependent on the lookahead. Often different states are identical, except they have a different lookahead. i.e.

Sample LR(1) item sets:


1)
A -> B.C,'x'
A -> E.C,'y'


2)
A -> B.C,'g'
A -> E.C,'h'


Equivalent LALR(1) item set:


1)
A -> B.C,'x'
A -> E.C,'y'
A -> B.C,'g'
A -> E.C,'h'


Fewer states means fewer shifts and reduces. And at least as importantly, a much smaller parse table.

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Q: Justfy that LALR parsers are faster than LR parsers?
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