语法分析器（syntax analyzer）【Java实现】

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import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
import java.util.StringTokenizer;
import java.util.List;
import java.util.ArrayList;
import java.util.Map;
import java.util.HashMap;
 
class Parser {
	private List<Token> source;
	private Token token;
	private int position;
 
	static class Node {
		public NodeType nt;
		public Node left, right;
		public String value;
 
		Node() {
			this.nt = null;
			this.left = null;
			this.right = null;
			this.value = null;
		}
		Node(NodeType node_type, Node left, Node right, String value) {
			this.nt = node_type;
			this.left = left;
			this.right = right;
			this.value = value;
		}
		public static Node make_node(NodeType nodetype, Node left, Node right) {
			return new Node(nodetype, left, right, "");
		}
		public static Node make_node(NodeType nodetype, Node left) {
			return new Node(nodetype, left, null, "");
		}
		public static Node make_leaf(NodeType nodetype, String value) {
			return new Node(nodetype, null, null, value);
		}
	}
 
	static class Token {
		public TokenType tokentype;
		public String value;
		public int line;
		public int pos;
 
		Token(TokenType token, String value, int line, int pos) {
			this.tokentype = token; this.value = value; this.line = line; this.pos = pos;
		}
		@Override
		public String toString() {
			return String.format("%5d  %5d %-15s %s", this.line, this.pos, this.tokentype, this.value);
		}
	}
 
	static enum TokenType {
		End_of_input(false, false, false, -1, NodeType.nd_None),
		Op_multiply(false, true, false, 13, NodeType.nd_Mul),
		Op_divide(false, true, false, 13, NodeType.nd_Div),
		Op_mod(false, true, false, 13, NodeType.nd_Mod),
		Op_add(false, true, false, 12, NodeType.nd_Add),
		Op_subtract(false, true, false, 12, NodeType.nd_Sub),
		Op_negate(false, false, true, 14, NodeType.nd_Negate),
		Op_not(false, false, true, 14, NodeType.nd_Not),
		Op_less(false, true, false, 10, NodeType.nd_Lss),
		Op_lessequal(false, true, false, 10, NodeType.nd_Leq),
		Op_greater(false, true, false, 10, NodeType.nd_Gtr),
		Op_greaterequal(false, true, false, 10, NodeType.nd_Geq),
		Op_equal(false, true, true, 9, NodeType.nd_Eql),
		Op_notequal(false, true, false, 9, NodeType.nd_Neq),
		Op_assign(false, false, false, -1, NodeType.nd_Assign),
		Op_and(false, true, false, 5, NodeType.nd_And),
		Op_or(false, true, false, 4, NodeType.nd_Or),
		Keyword_if(false, false, false, -1, NodeType.nd_If),
		Keyword_else(false, false, false, -1, NodeType.nd_None),
		Keyword_while(false, false, false, -1, NodeType.nd_While),
		Keyword_print(false, false, false, -1, NodeType.nd_None),
		Keyword_putc(false, false, false, -1, NodeType.nd_None),
		LeftParen(false, false, false, -1, NodeType.nd_None),
		RightParen(false, false, false, -1, NodeType.nd_None),
		LeftBrace(false, false, false, -1, NodeType.nd_None),
		RightBrace(false, false, false, -1, NodeType.nd_None),
		Semicolon(false, false, false, -1, NodeType.nd_None),
		Comma(false, false, false, -1, NodeType.nd_None),
		Identifier(false, false, false, -1, NodeType.nd_Ident),
		Integer(false, false, false, -1, NodeType.nd_Integer),
		String(false, false, false, -1, NodeType.nd_String);
 
		private final int precedence;
		private final boolean right_assoc;
		private final boolean is_binary;
		private final boolean is_unary;
		private final NodeType node_type;
 
		TokenType(boolean right_assoc, boolean is_binary, boolean is_unary, int precedence, NodeType node) {
			this.right_assoc = right_assoc;
			this.is_binary = is_binary;
			this.is_unary = is_unary;
			this.precedence = precedence;
			this.node_type = node;
		}
		boolean isRightAssoc() { return this.right_assoc; }
		boolean isBinary() { return this.is_binary; }
		boolean isUnary() { return this.is_unary; }
		int getPrecedence() { return this.precedence; }
		NodeType getNodeType() { return this.node_type; }
	}
	static enum NodeType {
		nd_None(""), nd_Ident("Identifier"), nd_String("String"), nd_Integer("Integer"), nd_Sequence("Sequence"), nd_If("If"),
		nd_Prtc("Prtc"), nd_Prts("Prts"), nd_Prti("Prti"), nd_While("While"),
		nd_Assign("Assign"), nd_Negate("Negate"), nd_Not("Not"), nd_Mul("Multiply"), nd_Div("Divide"), nd_Mod("Mod"), nd_Add("Add"),
		nd_Sub("Subtract"), nd_Lss("Less"), nd_Leq("LessEqual"),
		nd_Gtr("Greater"), nd_Geq("GreaterEqual"), nd_Eql("Equal"), nd_Neq("NotEqual"), nd_And("And"), nd_Or("Or");
 
		private final String name;
 
		NodeType(String name) {
			this.name = name;
		}
 
		@Override
		public String toString() { return this.name; }
	}
	static void error(int line, int pos, String msg) {
		if (line > 0 && pos > 0) {
			System.out.printf("%s in line %d, pos %d\n", msg, line, pos);
		} else {
			System.out.println(msg);
		}
		System.exit(1);
	}
	Parser(List<Token> source) {
		this.source = source;
		this.token = null;
		this.position = 0;
	}
	Token getNextToken() {
		this.token = this.source.get(this.position++);
		return this.token;
	}
	Node expr(int p) {
		Node result = null, node;
		TokenType op;
		int q;
 
		if (this.token.tokentype == TokenType.LeftParen) {
			result = paren_expr();
		} else if (this.token.tokentype == TokenType.Op_add || this.token.tokentype == TokenType.Op_subtract) {
			op = (this.token.tokentype == TokenType.Op_subtract) ? TokenType.Op_negate : TokenType.Op_add;
			getNextToken();
			node = expr(TokenType.Op_negate.getPrecedence());
			result = (op == TokenType.Op_negate) ? Node.make_node(NodeType.nd_Negate, node) : node;
		} else if (this.token.tokentype == TokenType.Op_not) {
			getNextToken();
			result = Node.make_node(NodeType.nd_Not, expr(TokenType.Op_not.getPrecedence()));
		} else if (this.token.tokentype == TokenType.Identifier) {
			result = Node.make_leaf(NodeType.nd_Ident, this.token.value);
			getNextToken();
		} else if (this.token.tokentype == TokenType.Integer) {
			result = Node.make_leaf(NodeType.nd_Integer, this.token.value);
			getNextToken();
		} else {
			error(this.token.line, this.token.pos, "Expecting a primary, found: " + this.token.tokentype);
		}
 
		while (this.token.tokentype.isBinary() && this.token.tokentype.getPrecedence() >= p) {
			op = this.token.tokentype;
			getNextToken();
			q = op.getPrecedence();
			if (!op.isRightAssoc()) {
				q++;
			}
			node = expr(q);
			result = Node.make_node(op.getNodeType(), result, node);
		}
		return result;
	}
	Node paren_expr() {
		expect("paren_expr", TokenType.LeftParen);
		Node node = expr(0);
		expect("paren_expr", TokenType.RightParen);
		return node;
	}
	void expect(String msg, TokenType s) {
		if (this.token.tokentype == s) {
			getNextToken();
			return;
		}
		error(this.token.line, this.token.pos, msg + ": Expecting '" + s + "', found: '" + this.token.tokentype + "'");
	}
	Node stmt() {
		Node s, s2, t = null, e, v;
		if (this.token.tokentype == TokenType.Keyword_if) {
			getNextToken();
			e = paren_expr();
			s = stmt();
			s2 = null;
			if (this.token.tokentype == TokenType.Keyword_else) {
				getNextToken();
				s2 = stmt();
			}
			t = Node.make_node(NodeType.nd_If, e, Node.make_node(NodeType.nd_If, s, s2));
		} else if (this.token.tokentype == TokenType.Keyword_putc) {
			getNextToken();
			e = paren_expr();
			t = Node.make_node(NodeType.nd_Prtc, e);
			expect("Putc", TokenType.Semicolon);
		} else if (this.token.tokentype == TokenType.Keyword_print) {
			getNextToken();
			expect("Print", TokenType.LeftParen);
			while (true) {
				if (this.token.tokentype == TokenType.String) {
					e = Node.make_node(NodeType.nd_Prts, Node.make_leaf(NodeType.nd_String, this.token.value));
					getNextToken();
				} else {
					e = Node.make_node(NodeType.nd_Prti, expr(0), null);
				}
				t = Node.make_node(NodeType.nd_Sequence, t, e);
				if (this.token.tokentype != TokenType.Comma) {
					break;
				}
				getNextToken();
			}
			expect("Print", TokenType.RightParen);
			expect("Print", TokenType.Semicolon);
		} else if (this.token.tokentype == TokenType.Semicolon) {
			getNextToken();
		} else if (this.token.tokentype == TokenType.Identifier) {
			v = Node.make_leaf(NodeType.nd_Ident, this.token.value);
			getNextToken();
			expect("assign", TokenType.Op_assign);
			e = expr(0);
			t = Node.make_node(NodeType.nd_Assign, v, e);
			expect("assign", TokenType.Semicolon);
		} else if (this.token.tokentype == TokenType.Keyword_while) {
			getNextToken();
			e = paren_expr();
			s = stmt();
			t = Node.make_node(NodeType.nd_While, e, s);
		} else if (this.token.tokentype == TokenType.LeftBrace) {
			getNextToken();
			while (this.token.tokentype != TokenType.RightBrace && this.token.tokentype != TokenType.End_of_input) {
				t = Node.make_node(NodeType.nd_Sequence, t, stmt());
			}
			expect("LBrace", TokenType.RightBrace);
		} else if (this.token.tokentype == TokenType.End_of_input) {
		} else {
			error(this.token.line, this.token.pos, "Expecting start of statement, found: " + this.token.tokentype);
		}
		return t;
	}
	Node parse() {
		Node t = null;
		getNextToken();
		while (this.token.tokentype != TokenType.End_of_input) {
			t = Node.make_node(NodeType.nd_Sequence, t, stmt());
		}
		return t;
	}
	void printAST(Node t) {
		int i = 0;
		if (t == null) {
			System.out.println(";");
		} else {
			System.out.printf("%-14s", t.nt);
			if (t.nt == NodeType.nd_Ident || t.nt == NodeType.nd_Integer || t.nt == NodeType.nd_String) {
				System.out.println(" " + t.value);
			} else {
				System.out.println();
				printAST(t.left);
				printAST(t.right);
			}
		}
	}
	public static void main(String[] args) {
		if (args.length > 0) {
			try {
				String value, token;
				int line, pos;
				Token t;
				boolean found;
				List<Token> list = new ArrayList<>();
				Map<String, TokenType> str_to_tokens = new HashMap<>();
 
				str_to_tokens.put("End_of_input", TokenType.End_of_input);
				str_to_tokens.put("Op_multiply", TokenType.Op_multiply);
				str_to_tokens.put("Op_divide", TokenType.Op_divide);
				str_to_tokens.put("Op_mod", TokenType.Op_mod);
				str_to_tokens.put("Op_add", TokenType.Op_add);
				str_to_tokens.put("Op_subtract", TokenType.Op_subtract);
				str_to_tokens.put("Op_negate", TokenType.Op_negate);
				str_to_tokens.put("Op_not", TokenType.Op_not);
				str_to_tokens.put("Op_less", TokenType.Op_less);
				str_to_tokens.put("Op_lessequal", TokenType.Op_lessequal);
				str_to_tokens.put("Op_greater", TokenType.Op_greater);
				str_to_tokens.put("Op_greaterequal", TokenType.Op_greaterequal);
				str_to_tokens.put("Op_equal", TokenType.Op_equal);
				str_to_tokens.put("Op_notequal", TokenType.Op_notequal);
				str_to_tokens.put("Op_assign", TokenType.Op_assign);
				str_to_tokens.put("Op_and", TokenType.Op_and);
				str_to_tokens.put("Op_or", TokenType.Op_or);
				str_to_tokens.put("Keyword_if", TokenType.Keyword_if);
				str_to_tokens.put("Keyword_else", TokenType.Keyword_else);
				str_to_tokens.put("Keyword_while", TokenType.Keyword_while);
				str_to_tokens.put("Keyword_print", TokenType.Keyword_print);
				str_to_tokens.put("Keyword_putc", TokenType.Keyword_putc);
				str_to_tokens.put("LeftParen", TokenType.LeftParen);
				str_to_tokens.put("RightParen", TokenType.RightParen);
				str_to_tokens.put("LeftBrace", TokenType.LeftBrace);
				str_to_tokens.put("RightBrace", TokenType.RightBrace);
				str_to_tokens.put("Semicolon", TokenType.Semicolon);
				str_to_tokens.put("Comma", TokenType.Comma);
				str_to_tokens.put("Identifier", TokenType.Identifier);
				str_to_tokens.put("Integer", TokenType.Integer);
				str_to_tokens.put("String", TokenType.String);
 
				Scanner s = new Scanner(new File(args[0]));
				String source = " ";
				while (s.hasNext()) {
					String str = s.nextLine();
					StringTokenizer st = new StringTokenizer(str);
					line = Integer.parseInt(st.nextToken());
					pos = Integer.parseInt(st.nextToken());
					token = st.nextToken();
					value = "";
					while (st.hasMoreTokens()) {
						value += st.nextToken() + " ";
					}
					found = false;
					if (str_to_tokens.containsKey(token)) {
						found = true;
						list.add(new Token(str_to_tokens.get(token), value, line, pos));
					}
					if (found == false) {
						throw new Exception("Token not found: '" + token + "'");
					}
				}
				Parser p = new Parser(list);
				p.printAST(p.parse());
			} catch (FileNotFoundException e) {
				error(-1, -1, "Exception: " + e.getMessage());
			} catch (Exception e) {
				error(-1, -1, "Exception: " + e.getMessage());
			}
		} else {
			error(-1, -1, "No args");
		}
	}
}