66 lines
2.7 KiB
Plaintext
66 lines
2.7 KiB
Plaintext
*******************************************************************************
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* *
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* EXPLANATION OF THE NODE STRUCTURES *
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* - Andrew Yu (11/94) *
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* *
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* Copyright (c) 1994, Regents of the University of California *
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* *
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* $Id: README,v 1.1.1.1 1996/07/09 06:21:32 scrappy Exp $
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* *
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*******************************************************************************
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INTRODUCTION
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The current node structures are plain old C structures. "Inheritance" is
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achieved by convention. No additional functions will be generated. Functions
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that manipulate node structures reside in this directory.
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FILES IN THIS DIRECTORY
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Node manipulation functions:
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copyfuncs.c - copying a node
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equalfuncs.c - comparing a node
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outfuncs.c - convert a node to ascii representation
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readfuncs.c - convert ascii representation back to a node
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makefuncs.c - creator functions for primitive nodes
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Node definitions:
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nodes.h - define node tags (NodeTag)
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pg_list.h - generic list
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primnodes.h - primitive nodes
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parsenodes.h - parse tree nodes
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plannodes.h - plan tree nodes
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relation.h - inner plan tree nodes
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execnodes.h - executor nodes
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memnodes.h - memory nodes
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STEPS TO ADD A NODE
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Suppose you wana define a node Foo:
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1. add a tag (T_Foo) to the enum NodeTag in nodes.h (You may have to
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recompile the whole tree after doing this.)
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2. add the structure definition to the appropriate ???nodes.h file. If you
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intend to inherit from, say a Plan node, put Plan as the first field of
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you definition.
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3. if you intend to use copyObject, equal, nodeToString or stringToNode,
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add an appropriate function to copyfuncs.c, equalfuncs.c, outfuncs.c
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and readfuncs.c accordingly. (Except for frequently used nodes, don't
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bother writing a creator function in makefuncs.c)
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HISTORICAL NOTE
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Prior to the current simple C structure definitions, the Node structures
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uses a pseudo-inheritance system which automatically generates creator and
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accessor functions. Since every node inherits from LispValue, the whole thing
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is a mess. Here's a little anecdote:
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LispValue definition -- class used to support lisp structures
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in C. This is here because we did not want to totally rewrite
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planner and executor code which depended on lisp structures when
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we ported postgres V1 from lisp to C. -cim 4/23/90
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