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I know and use bison/yacc. But in parsing world, there's a lot of buzz around packrat parsing.
What is it? Is it worth studing?
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Recursive descent is a top-down parsing technique that constructs the parse tree from the top and the input is read from left to right. It uses procedures for every terminal and non-terminal entity. This parsing technique recursively parses the input to make a parse tree, which may or may not require back-tracking.
Packrat parsing is a way of providing asymptotically better performance for parsing expression grammars (PEGs); specifically for PEGs, linear time parsing can be guaranteed.
Essentially, Packrat parsing just means caching whether sub-expressions match at the current position in the string when they are tested -- this means that if the current attempt to fit the string into an expression fails then attempts to fit other possible expressions can benefit from the known pass/fail of subexpressions at the points in the string where they have already been tested.
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