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week6 kodutöö lahendus
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‎sols/week6/AktkHandwrittenParser.java‎

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package week6;
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import week5.AktkHandwrittenLexer;
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import week5.AktkToken;
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import java.io.StringReader;
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import static week5.AktkToken.Type.*;
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public class AktkHandwrittenParser {
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private final AktkHandwrittenLexer lexer;
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private AktkToken current;
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public AktkHandwrittenParser(AktkHandwrittenLexer lexer) {
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this.lexer = lexer;
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}
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private void consume() {
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current = lexer.readNextToken();
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}
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private AktkToken.Type peek() {
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return current.type();
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}
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private void match(AktkToken.Type t) {
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if (peek() != t) throw new AktkParseException(current, t);
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consume();
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}
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private AktkNode expression() {
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AktkNode left = term();
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AktkToken.Type next = peek();
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while (next == PLUS || next == MINUS) {
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consume();
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left = new AktkNode.BinOp(next, left, term());
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next = peek();
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}
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if (next == EOF || next == RPAREN) {
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return left;
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}
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throw new AktkParseException(current, PLUS, MINUS, TIMES, DIV, EOF, RPAREN);
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}
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private AktkNode term() {
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AktkNode left = factor();
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AktkToken.Type next = peek();
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while (next == TIMES || next == DIV) {
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consume();
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left = new AktkNode.BinOp(next, left, factor());
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next = peek();
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}
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return left;
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}
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private AktkNode factor() {
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AktkToken.Type t = peek();
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AktkNode result;
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switch (t) {
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case VARIABLE:
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result = new AktkNode.Variable((String) current.data());
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consume();
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break;
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case INTEGER:
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result = new AktkNode.IntLiteral((int) current.data());
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consume();
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break;
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case LPAREN:
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match(LPAREN);
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result = expression();
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match(RPAREN);
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break;
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default:
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throw new AktkParseException(current, VARIABLE, INTEGER, LPAREN);
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}
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return result;
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}
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public AktkNode parse() {
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consume();
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AktkNode result = expression();
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if (peek() != EOF) {
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throw new AktkParseException(current, EOF);
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}
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return result;
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}
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public static AktkNode parse(String input) {
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AktkHandwrittenLexer lexer = new AktkHandwrittenLexer(new StringReader(input));
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AktkHandwrittenParser parser = new AktkHandwrittenParser(lexer);
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return parser.parse();
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}
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}

‎sols/week6/AktkNode.java‎

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package week6;
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import week5.AktkToken;
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import java.util.Map;
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import static week5.AktkToken.Type.*;
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public interface AktkNode {
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static AktkNode num(int value) {
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return new IntLiteral(value);
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}
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static AktkNode var(String name) {
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return new Variable(name);
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}
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private static AktkNode binop(AktkToken.Type type, AktkNode left, AktkNode right) {
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return new BinOp(type, left, right);
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}
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static AktkNode plus(AktkNode left, AktkNode right) {
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return binop(PLUS, left, right);
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}
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static AktkNode minus(AktkNode left, AktkNode right) {
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return binop(MINUS, left, right);
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}
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static AktkNode mul(AktkNode left, AktkNode right) {
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return binop(TIMES, left, right);
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}
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static AktkNode div(AktkNode left, AktkNode right) {
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return binop(DIV, left, right);
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}
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int eval(Map<String, Integer> env);
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default String toPrettyString() {
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return toPrettyString(0);
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}
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String toPrettyString(int contextPriority);
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record IntLiteral(int value) implements AktkNode {
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@Override
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public int eval(Map<String, Integer> env) {
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return value;
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}
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@Override
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public String toString() {
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return "num(" + value + ")";
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}
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@Override
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public String toPrettyString(int contextPriority) {
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return Integer.toString(value);
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}
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}
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record Variable(String name) implements AktkNode {
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@Override
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public int eval(Map<String, Integer> env) {
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return env.get(name());
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}
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@Override
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public String toString() {
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return "var(\"" + name + "\")";
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}
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@Override
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public String toPrettyString(int contextPriority) {
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return name;
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}
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}
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record BinOp(AktkToken.Type op, AktkNode left, AktkNode right) implements AktkNode {
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public BinOp {
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if (!isOperator(op)) throw new IllegalArgumentException();
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}
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private boolean isOperator(AktkToken.Type token) {
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return switch (token) {
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case PLUS, MINUS, TIMES, DIV -> true;
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default -> false;
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};
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}
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@Override
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public int eval(Map<String, Integer> env) {
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int l = left.eval(env);
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int r = right.eval(env);
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return switch (op) {
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case PLUS -> l + r;
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case MINUS -> l - r;
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case TIMES -> l * r;
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case DIV -> l / r;
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default -> throw new AssertionError("Impossible!");
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};
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}
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@Override
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public String toString() {
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return op.toString().toLowerCase() + "(" + left + ", " + right + ")";
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}
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@Override
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public String toPrettyString(int contextPriority) {
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int prio = priorityOf(op);
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int assoc = prio + (isAssoc(op) ? 0 : 1);
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String content = left.toPrettyString(prio) + symbolOf(op) + right.toPrettyString(assoc);
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if (contextPriority > prio) return "(" + content + ")";
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else return content;
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}
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private boolean isAssoc(AktkToken.Type op) {
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return switch (op) {
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case MINUS, DIV -> false;
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default -> true;
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};
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}
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private String symbolOf(AktkToken.Type op) {
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return switch (op) {
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case PLUS -> "+";
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case MINUS -> "-";
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case TIMES -> "*";
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case DIV -> "/";
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default -> null;
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};
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}
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private int priorityOf(AktkToken.Type op) {
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return switch (op) {
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case PLUS, MINUS -> 1;
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case TIMES, DIV -> 2;
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default -> 0;
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};
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}
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}
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}

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