question about lookahead
15 Feb 1999 23:33:00 -0500

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Newsgroups: comp.compilers
Date: 15 Feb 1999 23:33:00 -0500
Organization: Deja News - The Leader in Internet Discussion
Keywords: parse, question

Hi All:

I Am A Beginner With Compiler Theory.

It Seems Like Lookahead Is Used By Various Parsing Methods
To Choose (Disambiguate) Between Several Productions That
Can Be Taken At Any Point.

My Question Is Why Lookahead At All ? Just Use A
*Non Deterministic* PDA As Your Engine. (Just As You Use
NFA'S To Find Reg-Expressions). A NPDA Would Then Choose
All Productions That Were Applicable, As Opposed To Looking
Ahead And Deciding Which One To Choose Beforehand.

The NPDA Would Of Course Be Converted Into An *Equivalent*
Deterministic PDA In Order To Actually Run It...

So To Recap The Question Is:

-- why use lookahead when a NPDA can be used to choose all
      productions at the same time (similar to what is done for
      reg exps) ?

Best Regards,

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