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Recursive Descent

Recursive Descent is a method of writing a top-down parsing program in which a grammar rule is written as a function.

Given a grammar rule: 


   S -> NP VP
we simply make the left-hand-side nonterminal be the name of the function, and write a series of function calls for the right-hand side. 

   (defn s []
     (and (np)
          (vp)) )

There could be an infinite loop if there is left recursion, i.e. a rule of the form: 


   A -> A ...