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Annotation of 43BSDTahoe/ucb/pascal/src/yytree.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1980 Regents of the University of California.
        !             3:  * All rights reserved.  The Berkeley software License Agreement
        !             4:  * specifies the terms and conditions for redistribution.
        !             5:  */
        !             6: 
        !             7: #ifndef lint
        !             8: static char sccsid[] = "@(#)yytree.c   5.1 (Berkeley) 6/5/85";
        !             9: #endif not lint
        !            10: 
        !            11: #include "whoami.h"
        !            12: #include "0.h"
        !            13: #include "tree.h"
        !            14: #include "tree_ty.h"
        !            15: 
        !            16: extern int *spacep;
        !            17: 
        !            18: /*
        !            19:  * LIST MANIPULATION ROUTINES
        !            20:  *
        !            21:  * The grammar for Pascal is written left recursively.
        !            22:  * Because of this, the portions of parse trees which are to resemble
        !            23:  * lists are in the somewhat inconvenient position of having
        !            24:  * the nodes built from left to right, while we want to eventually
        !            25:  * have as semantic value the leftmost node.
        !            26:  * We could carry the leftmost node as semantic value, but this
        !            27:  * would be inefficient as to add a new node to the list we would
        !            28:  * have to chase down to the end.  Other solutions involving a head
        !            29:  * and tail pointer waste space.
        !            30:  *
        !            31:  * The simple solution to this apparent dilemma is to carry along
        !            32:  * a pointer to the leftmost node in a list in the rightmost node
        !            33:  * which is the current semantic value of the list.
        !            34:  * When we have completed building the list, we can retrieve this
        !            35:  * left end pointer very easily; neither adding new elements to the list
        !            36:  * nor finding the left end is thus expensive.  As the bottommost node
        !            37:  * has an unused next pointer in it, no space is wasted either.
        !            38:  *
        !            39:  * The nodes referred to here are of the T_LISTPP type and have
        !            40:  * the form:
        !            41:  *
        !            42:  *     T_LISTPP        some_pointer            next_element
        !            43:  *
        !            44:  * Here some_pointer points to the things of interest in the list,
        !            45:  * and next_element to the next thing in the list except for the
        !            46:  * rightmost node, in which case it points to the leftmost node.
        !            47:  * The next_element of the rightmost node is of course zapped to the
        !            48:  * NIL pointer when the list is completed.
        !            49:  *
        !            50:  * Thinking of the lists as tree we heceforth refer to the leftmost
        !            51:  * node as the "top", and the rightmost node as the "bottom" or as
        !            52:  * the "virtual root".
        !            53:  */
        !            54: 
        !            55: /*
        !            56:  * Make a new list
        !            57:  */
        !            58: struct tnode *
        !            59: newlist(new)
        !            60:        register struct tnode *new;
        !            61: {
        !            62: 
        !            63:        if (new == TR_NIL)
        !            64:                return (TR_NIL);
        !            65:        return ((struct tnode *) tree3(T_LISTPP, (int) new,
        !            66:                                        (struct tnode *) spacep));
        !            67: }
        !            68: 
        !            69: /*
        !            70:  * Add a new element to an existing list
        !            71:  */
        !            72: struct tnode *
        !            73: addlist(vroot, new)
        !            74:        register struct tnode *vroot;
        !            75:        struct tnode *new;
        !            76: {
        !            77:        register struct tnode *top;
        !            78: 
        !            79:        if (new == TR_NIL)
        !            80:                return (vroot);
        !            81:        if (vroot == TR_NIL)
        !            82:                return (newlist(new));
        !            83:        top = vroot->list_node.next;
        !            84:        vroot->list_node.next = (struct tnode *) spacep;
        !            85:        return ((struct tnode *) tree3(T_LISTPP, (int) new, top));
        !            86: }
        !            87: 
        !            88: /*
        !            89:  * Fix up the list which has virtual root vroot.
        !            90:  * We grab the top pointer and return it, zapping the spot
        !            91:  * where it was so that the tree is not circular.
        !            92:  */
        !            93: struct tnode *
        !            94: fixlist(vroot)
        !            95:        register struct tnode *vroot;
        !            96: {
        !            97:        register struct tnode *top;
        !            98: 
        !            99:        if (vroot == TR_NIL)
        !           100:                return (TR_NIL);
        !           101:        top = vroot->list_node.next;
        !           102:        vroot->list_node.next = TR_NIL;
        !           103:        return (top);
        !           104: }
        !           105: 
        !           106: 
        !           107: /*
        !           108:  * Set up a T_VAR node for a qualified variable.
        !           109:  * Init is the initial entry in the qualification,
        !           110:  * or NIL if there is none.
        !           111:  *
        !           112:  * if we are building pTrees, there has to be an extra slot for 
        !           113:  * a pointer to the namelist entry of a field, if this T_VAR refers
        !           114:  * to a field name within a WITH statement.
        !           115:  * this extra field is set in lvalue, and used in VarCopy.
        !           116:  */
        !           117: struct tnode *
        !           118: setupvar(var, init)
        !           119:        char *var;
        !           120:        register struct tnode *init;
        !           121: {
        !           122: 
        !           123:        if (init != TR_NIL)
        !           124:                init = newlist(init);
        !           125: #      ifndef PTREE
        !           126:            return (tree4(T_VAR, NOCON, (struct tnode *) var, init));
        !           127: #      else
        !           128:            return tree5( T_VAR, NOCON, (struct tnode *) var, init, TR_NIL );
        !           129: #      endif
        !           130: }
        !           131: 
        !           132:     /*
        !           133:      * set up a T_TYREC node for a record
        !           134:      *
        !           135:      * if we are building pTrees, there has to be an extra slot for 
        !           136:      * a pointer to the namelist entry of the record.
        !           137:      * this extra field is filled in in gtype, and used in RecTCopy.
        !           138:      */
        !           139: struct tnode *
        !           140: setuptyrec( line , fldlist )
        !           141:     int        line;
        !           142:     struct tnode *fldlist;
        !           143:     {
        !           144: 
        !           145: #      ifndef PTREE
        !           146:            return tree3( T_TYREC , line , fldlist );
        !           147: #      else
        !           148:            return tree4( T_TYREC , line , fldlst , TR_NIL );
        !           149: #      endif
        !           150:     }
        !           151: 
        !           152:     /*
        !           153:      * set up a T_FIELD node for a field.
        !           154:      *
        !           155:      * if we are building pTrees, there has to be an extra slot for
        !           156:      * a pointer to the namelist entry of the field.
        !           157:      * this extra field is set in lvalue, and used in SelCopy.
        !           158:      */
        !           159: struct tnode *
        !           160: setupfield( field , other )
        !           161:     struct tnode *field;
        !           162:     struct tnode *other;
        !           163:     {
        !           164: 
        !           165: #      ifndef PTREE
        !           166:            return tree3( T_FIELD , (int) field , other );
        !           167: #      else
        !           168:            return tree4( T_FIELD , (int) field , other , TR_NIL );
        !           169: #      endif
        !           170:     }

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