# Re: predictive parsing and non-recursive predictive parsing

## max@gustavus.edu

Tue, 24 Jun 2008 19:28:06 -0700 (PDT)

*From comp.compilers*

| List of all articles for this month |

**From: ** | max@gustavus.edu |

**Newsgroups: ** | comp.compilers |

**Date: ** | Tue, 24 Jun 2008 19:28:06 -0700 (PDT) |

**Organization: ** | Compilers Central |

**References: ** | 08-06-053 08-06-055 |

**Keywords: ** | parse, LL(1) |

**Posted-Date: ** | 25 Jun 2008 17:15:36 EDT |

On Jun 24, 2:49 am, kamal <kama...@hp.com> wrote:

*> ...*

*> Recursive (descent) parsing is leftmost. You have the follow set in*

*> non-recursive parsing to figure out what *can* follow, and so opt to*

*> reduce by a different rule than the leftmost reduction. It helps in*

*> overcoming ambiguities that RDP have.*

(1) Yes, recursive descent parsing is leftmost, but that word

"leftmost" means that the leftmost nonterminal is expanded out at each

step, rather than anything about a "leftmost reduction" or, as your

phrase "reduce by a different rule" suggests you might have meant,

leftmost production. There is no reduction done at all in a recursive

descent parser, and the choice of productions is not influenced by

their order.

(2) The non-recursive parsing that was being discussed in the original

post was non-recursive *predictive* parsing, i.e., LL(1) top-down

parsing. As such, it has no reductions either and follows the same

sequence of parsing actions. It too is constructing a leftmost

derivation.

(3) Recursive descent parsers do not have ambiguities, because

ambiguity is a property of a grammar or a language, not a parser.

-Max Hailperin

Professor of Computer Science

Gustavus Adolphus College

Post a followup to this message

Return to the
comp.compilers page.

Search the
comp.compilers archives again.