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1.1 root 1: /* Copyright (c) 1979 Regents of the University of California */
2:
3: static char sccsid[] = "@(#)yytree.c 1.1 8/27/80";
4:
5: #include "whoami.h"
6: #include "0.h"
7: #include "tree.h"
8:
9: extern int *spacep;
10:
11: /*
12: * LIST MANIPULATION ROUTINES
13: *
14: * The grammar for Pascal is written left recursively.
15: * Because of this, the portions of parse trees which are to resemble
16: * lists are in the somewhat inconvenient position of having
17: * the nodes built from left to right, while we want to eventually
18: * have as semantic value the leftmost node.
19: * We could carry the leftmost node as semantic value, but this
20: * would be inefficient as to add a new node to the list we would
21: * have to chase down to the end. Other solutions involving a head
22: * and tail pointer waste space.
23: *
24: * The simple solution to this apparent dilemma is to carry along
25: * a pointer to the leftmost node in a list in the rightmost node
26: * which is the current semantic value of the list.
27: * When we have completed building the list, we can retrieve this
28: * left end pointer very easily; neither adding new elements to the list
29: * nor finding the left end is thus expensive. As the bottommost node
30: * has an unused next pointer in it, no space is wasted either.
31: *
32: * The nodes referred to here are of the T_LISTPP type and have
33: * the form:
34: *
35: * T_LISTPP some_pointer next_element
36: *
37: * Here some_pointer points to the things of interest in the list,
38: * and next_element to the next thing in the list except for the
39: * rightmost node, in which case it points to the leftmost node.
40: * The next_element of the rightmost node is of course zapped to the
41: * NIL pointer when the list is completed.
42: *
43: * Thinking of the lists as tree we heceforth refer to the leftmost
44: * node as the "top", and the rightmost node as the "bottom" or as
45: * the "virtual root".
46: */
47:
48: /*
49: * Make a new list
50: */
51: newlist(new)
52: register int *new;
53: {
54:
55: if (new == NIL)
56: return (NIL);
57: return (tree3(T_LISTPP, new, spacep));
58: }
59:
60: /*
61: * Add a new element to an existing list
62: */
63: addlist(vroot, new)
64: register int *vroot;
65: int *new;
66: {
67: register int *top;
68:
69: if (new == NIL)
70: return (vroot);
71: if (vroot == NIL)
72: return (newlist(new));
73: top = vroot[2];
74: vroot[2] = spacep;
75: return (tree3(T_LISTPP, new, top));
76: }
77:
78: /*
79: * Fix up the list which has virtual root vroot.
80: * We grab the top pointer and return it, zapping the spot
81: * where it was so that the tree is not circular.
82: */
83: fixlist(vroot)
84: register int *vroot;
85: {
86: register int *top;
87:
88: if (vroot == NIL)
89: return (NIL);
90: top = vroot[2];
91: vroot[2] = NIL;
92: return (top);
93: }
94:
95:
96: /*
97: * Set up a T_VAR node for a qualified variable.
98: * Init is the initial entry in the qualification,
99: * or NIL if there is none.
100: *
101: * if we are building pTrees, there has to be an extra slot for
102: * a pointer to the namelist entry of a field, if this T_VAR refers
103: * to a field name within a WITH statement.
104: * this extra field is set in lvalue, and used in VarCopy.
105: */
106: setupvar(var, init)
107: char *var;
108: register int *init;
109: {
110:
111: if (init != NIL)
112: init = newlist(init);
113: # ifndef PTREE
114: return (tree4(T_VAR, NOCON, var, init));
115: # else
116: return tree5( T_VAR , NOCON , var , init , NIL );
117: # endif
118: }
119:
120: /*
121: * set up a T_TYREC node for a record
122: *
123: * if we are building pTrees, there has to be an extra slot for
124: * a pointer to the namelist entry of the record.
125: * this extra field is filled in in gtype, and used in RecTCopy.
126: */
127: setuptyrec( line , fldlst )
128: int line;
129: int *fldlst;
130: {
131:
132: # ifndef PTREE
133: return tree3( T_TYREC , line , fldlst );
134: # else
135: return tree4( T_TYREC , line , fldlst , NIL );
136: # endif
137: }
138:
139: /*
140: * set up a T_FIELD node for a field.
141: *
142: * if we are building pTrees, there has to be an extra slot for
143: * a pointer to the namelist entry of the field.
144: * this extra field is set in lvalue, and used in SelCopy.
145: */
146: setupfield( field , other )
147: int *field;
148: int *other;
149: {
150:
151: # ifndef PTREE
152: return tree3( T_FIELD , field , other );
153: # else
154: return tree4( T_FIELD , field , other , NIL );
155: # endif
156: }
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