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1
21
22 package org.armedbear.lisp;
23
24 public final class Nil extends Symbol
25 {
26 public Nil(Package  pkg)
27 {
28 super("NIL", pkg);
29 pkg.addSymbol(this);
30 setSymbolValue(this);
31 setSpecial(true);
32 setConstant(true);
33 }
34
35 public LispObject typeOf()
36 {
37 return Symbol.NULL;
38 }
39
40 public LispClass classOf()
41 {
42 return BuiltInClass.NULL;
43 }
44
45 public LispObject getDescription()
46 {
47 return new SimpleString("The symbol NIL");
48 }
49
50 public boolean getBooleanValue()
51 {
52 return false;
53 }
54
55 public LispObject typep(LispObject typeSpecifier) throws ConditionThrowable
56 {
57 if (typeSpecifier == Symbol.NULL)
58 return T;
59 if (typeSpecifier == Symbol.LIST)
60 return T;
61 if (typeSpecifier == Symbol.SEQUENCE)
62 return T;
63 if (typeSpecifier == Symbol.SYMBOL)
64 return T;
65 if (typeSpecifier == Symbol.BOOLEAN)
66 return T;
67 if (typeSpecifier == BuiltInClass.NULL)
68 return T;
69 if (typeSpecifier == BuiltInClass.LIST)
70 return T;
71 if (typeSpecifier == BuiltInClass.SEQUENCE)
72 return T;
73 if (typeSpecifier == BuiltInClass.SYMBOL)
74 return T;
75 return super.typep(typeSpecifier);
76 }
77
78 public boolean constantp()
79 {
80 return true;
81 }
82
83 public final LispObject getSymbolValue()
84 {
85 return this;
86 }
87
88 public LispObject car()
89 {
90 return this;
91 }
92
93 public LispObject cdr()
94 {
95 return this;
96 }
97
98 public final LispObject cadr()
99 {
100 return this;
101 }
102
103 public final LispObject cddr()
104 {
105 return this;
106 }
107
108 public int length()
109 {
110 return 0;
111 }
112
113 public LispObject push(LispObject obj)
114 {
115 return new Cons(obj);
116 }
117
118 public LispObject elt(int index) throws ConditionThrowable
119 {
120 return signal(new TypeError("ELT: invalid index " + index + " for " + this + "."));
121 }
122
123 public LispObject nreverse()
124 {
125 return this;
126 }
127
128 public LispObject[] copyToArray()
129 {
130 return new LispObject[0];
131 }
132
133 public boolean listp()
134 {
135 return true;
136 }
137
138 public LispObject LISTP()
139 {
140 return T;
141 }
142
143 public boolean endp()
144 {
145 return true;
146 }
147
148 public LispObject ENDP()
149 {
150 return T;
151 }
152
153 public LispObject NOT()
154 {
155 return T;
156 }
157
158 public final LispObject getSymbolFunction()
159 {
160 return null;
161 }
162
163 public String toString()
164 {
165 if (_PRINT_READABLY_.symbolValueNoThrow() != NIL)
166 return "|COMMON-LISP|::|NIL|";
167 return "NIL";
168 }
169 }
170 |
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