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74 lines
874 B
74 lines
874 B
// SysY 子集语法：支持形如
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// int main() { int a = 1; int b = 2; return a + b; }
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// 的最小返回表达式编译。
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// 后续需要自行添加
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grammar SysY;
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compUnit
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: funcDef EOF
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;
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funcDef
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: Int Main L_PAREN R_PAREN block
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;
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block
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: L_BRACE stmt* R_BRACE
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;
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stmt
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: varDecl
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| returnStmt
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;
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varDecl
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: Int Ident (Assign exp)? Semi
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;
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returnStmt
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: Return exp Semi
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;
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exp
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: addExp
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;
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addExp
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: primary (AddOp primary)*
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;
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primary
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: Number
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| Ident
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| L_PAREN exp R_PAREN
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;
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Int : 'int';
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Return : 'return';
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Main : 'main';
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AddOp : '+';
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Assign : '=';
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Semi : ';';
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L_PAREN : '(';
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R_PAREN : ')';
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L_BRACE : '{';
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R_BRACE : '}';
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Ident
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: [a-zA-Z_][a-zA-Z_0-9]*
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;
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Number
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: [0-9]+
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;
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WS
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: [ \t\r\n]+ -> skip
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;
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COMMENT
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: '//' ~[\r\n]* -> skip
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;
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