完善常量

RiddleLexer.g4

@@ -19,6 +19,7 @@ True:'true';
 False:'false';
 Static:'static';
 Const:'const';
+Null:'null';
 //可见字符
 //基本运算符
 LeftBracket:    '(';

RiddleParser.g4

@@ -147,6 +147,7 @@ expression
     | string                                                #stringExpr
     | number                                                #numberExpr
     | boolean                                               #booleanExpr
+    | Null                                                  #nullExpr
     ;
 
 id: Identifier;

parser/RiddleLexer.h

@@ -14,16 +14,16 @@ class  RiddleLexer : public antlr4::Lexer {
   enum {
     Var = 1, Val = 2, For = 3, While = 4, If = 5, Else = 6, Func = 7, Return = 8, 
     Import = 9, Package = 10, Class = 11, Public = 12, Protected = 13, Private = 14, 
-    Override = 15, True = 16, False = 17, Static = 18, Const = 19, LeftBracket = 20, 
-    RightBracket = 21, LeftSquare = 22, RightSquare = 23, LeftCurly = 24, 
-    RightCurly = 25, Colon = 26, Semi = 27, Comma = 28, Equal = 29, Assign = 30, 
-    Greater = 31, Less = 32, LeftLeft = 33, RightRight = 34, RightRightRight = 35, 
-    Add = 36, Sub = 37, Star = 38, Div = 39, Mod = 40, Not = 41, And = 42, 
-    Or = 43, Xor = 44, Dot = 45, DoubleQuotes = 46, Quotes = 47, Endl = 48, 
-    Identifier = 49, Hexadecimal = 50, Decimal = 51, Octal = 52, Binary = 53, 
-    Float = 54, IntegerSequence = 55, HEX_DIGIT = 56, OCTAL_DIGIT = 57, 
-    BINARY_DIGIT = 58, DIGIT = 59, STRING = 60, LINE_COMMENT = 61, BLOCK_COMMENT = 62, 
-    WHITESPACE = 63
+    Override = 15, True = 16, False = 17, Static = 18, Const = 19, Null = 20, 
+    LeftBracket = 21, RightBracket = 22, LeftSquare = 23, RightSquare = 24, 
+    LeftCurly = 25, RightCurly = 26, Colon = 27, Semi = 28, Comma = 29, 
+    Equal = 30, Assign = 31, Greater = 32, Less = 33, LeftLeft = 34, RightRight = 35, 
+    RightRightRight = 36, Add = 37, Sub = 38, Star = 39, Div = 40, Mod = 41, 
+    Not = 42, And = 43, Or = 44, Xor = 45, Dot = 46, DoubleQuotes = 47, 
+    Quotes = 48, Endl = 49, Identifier = 50, Hexadecimal = 51, Decimal = 52, 
+    Octal = 53, Binary = 54, Float = 55, IntegerSequence = 56, HEX_DIGIT = 57, 
+    OCTAL_DIGIT = 58, BINARY_DIGIT = 59, DIGIT = 60, STRING = 61, LINE_COMMENT = 62, 
+    BLOCK_COMMENT = 63, WHITESPACE = 64
   };
 
   explicit RiddleLexer(antlr4::CharStream *input);

parser/RiddleLexer.tokens

@@ -17,50 +17,51 @@ True=16
 False=17
 Static=18
 Const=19
-LeftBracket=20
-RightBracket=21
-LeftSquare=22
-RightSquare=23
-LeftCurly=24
-RightCurly=25
-Colon=26
-Semi=27
-Comma=28
-Equal=29
-Assign=30
-Greater=31
-Less=32
-LeftLeft=33
-RightRight=34
-RightRightRight=35
-Add=36
-Sub=37
-Star=38
-Div=39
-Mod=40
-Not=41
-And=42
-Or=43
-Xor=44
-Dot=45
-DoubleQuotes=46
-Quotes=47
-Endl=48
-Identifier=49
-Hexadecimal=50
-Decimal=51
-Octal=52
-Binary=53
-Float=54
-IntegerSequence=55
-HEX_DIGIT=56
-OCTAL_DIGIT=57
-BINARY_DIGIT=58
-DIGIT=59
-STRING=60
-LINE_COMMENT=61
-BLOCK_COMMENT=62
-WHITESPACE=63
+Null=20
+LeftBracket=21
+RightBracket=22
+LeftSquare=23
+RightSquare=24
+LeftCurly=25
+RightCurly=26
+Colon=27
+Semi=28
+Comma=29
+Equal=30
+Assign=31
+Greater=32
+Less=33
+LeftLeft=34
+RightRight=35
+RightRightRight=36
+Add=37
+Sub=38
+Star=39
+Div=40
+Mod=41
+Not=42
+And=43
+Or=44
+Xor=45
+Dot=46
+DoubleQuotes=47
+Quotes=48
+Endl=49
+Identifier=50
+Hexadecimal=51
+Decimal=52
+Octal=53
+Binary=54
+Float=55
+IntegerSequence=56
+HEX_DIGIT=57
+OCTAL_DIGIT=58
+BINARY_DIGIT=59
+DIGIT=60
+STRING=61
+LINE_COMMENT=62
+BLOCK_COMMENT=63
+WHITESPACE=64
 'var'=1
 'val'=2
 'for'=3
@@ -80,32 +81,33 @@ WHITESPACE=63
 'false'=17
 'static'=18
 'const'=19
-'('=20
-')'=21
-'['=22
-']'=23
-'{'=24
-'}'=25
-':'=26
-';'=27
-','=28
-'=='=29
-'='=30
-'>'=31
-'<'=32
-'<<'=33
-'>>'=34
-'>>>'=35
-'+'=36
-'-'=37
-'*'=38
-'/'=39
-'%'=40
-'!'=41
-'&'=42
-'|'=43
-'^'=44
-'.'=45
-'"'=46
-'\''=47
-'\n'=48
+'null'=20
+'('=21
+')'=22
+'['=23
+']'=24
+'{'=25
+'}'=26
+':'=27
+';'=28
+','=29
+'=='=30
+'='=31
+'>'=32
+'<'=33
+'<<'=34
+'>>'=35
+'>>>'=36
+'+'=37
+'-'=38
+'*'=39
+'/'=40
+'%'=41
+'!'=42
+'&'=43
+'|'=44
+'^'=45
+'.'=46
+'"'=47
+'\''=48
+'\n'=49