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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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