23 Apr 2006 10:05:53 -0400

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understanding the intuition behind LL(k) parsers and LR(k) parsers Mark.Felzer@gmail.com (Mark F.) (2006-04-21) |

Re: understanding the intuition behind LL(k) parsers and LR(k) parsers tom@infoether.com (Tom Copeland) (2006-04-22) |

Re: understanding the intuition behind LL(k) parsers and LR(k) parsers cfc@shell01.TheWorld.com (Chris F Clark) (2006-04-23) |

Re: understanding the intuition behind LL(k) parsers and LR(k) parsers max@gustavus.edu (Max Hailperin) (2006-04-23) |

Re: understanding the intuition behind LL(k) parsers and LR(k) parsers DrDiettrich@compuserve.de (Hans-Peter Diettrich) (2006-04-23) |

Re: understanding the intuition behind LL(k) parsers and LR(k) parsers pbmann@gmail.com (2006-04-28) |

Re: understanding the intuition behind LL(k) parsers and LR(k) parsers pbmann@gmail.com (2006-05-01) |

From: | Hans-Peter Diettrich <DrDiettrich@compuserve.de> |

Newsgroups: | comp.compilers |

Date: | 23 Apr 2006 10:05:53 -0400 |

Organization: | Compilers Central |

References: | 06-04-124 |

Keywords: | parse |

Posted-Date: | 23 Apr 2006 10:05:53 EDT |

"Mark F." wrote:

*> Maybe you can help me visualize the basic idea behind the two*

*> approaches to AST tree generation.*

Just an idea:

A top-down parser starts thinking about possible alternatives, *before*

inspecting an input symbol. He will immediately know, when only one or

zero alternatives remain, whereupon all read symbols can be discarded.

As a scout, he'll know where he is, but not where to go.

A bottom-up parser reads input symbols and determines the possible

alternatives *afterwards*, from what he already has read. If not a

single alternative remains, it continues reading, hoping that further

symbols will make sense later.

As a scout, he'll know where to go, but not which way.

DoDi

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