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215
java/expression/exceptions/ExpressionParser.java
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215
java/expression/exceptions/ExpressionParser.java
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package expression.exceptions;
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import expression.*;
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/**
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* @author Doschennikov Nikita (me@fymio.us)
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*/
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public class ExpressionParser implements ListParser {
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private String src;
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private int pos;
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private java.util.List<String> variables;
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@Override
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public ListExpression parse(String expression, java.util.List<String> variables) {
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// System.err.println("PARSE: [" + expression + "]");
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this.src = expression;
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this.pos = 0;
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this.variables = variables;
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AbstractExpression result = parseMinMax();
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skipWhitespace();
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if (pos < src.length()) {
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throw new IllegalArgumentException(
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"Unexpected character '" + src.charAt(pos) + "' at position " + pos);
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}
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return result;
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}
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private AbstractExpression parseMinMax() {
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AbstractExpression left = parseAddSub();
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while (true) {
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skipWhitespace();
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if (tryConsume("min")) left = new Min(left, parseAddSub());
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else if (tryConsume("max")) left = new Max(left, parseAddSub());
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else if (tryConsume("set")) left = new SetBit(left, parseAddSub());
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else if (tryConsume("clear")) left = new Clear(left, parseAddSub());
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else break;
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}
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return left;
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}
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private AbstractExpression parseAddSub() {
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AbstractExpression left = parseMulDiv();
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while (true) {
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skipWhitespace();
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if (pos < src.length() && src.charAt(pos) == '+') {
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pos++;
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left = new CheckedAdd(left, parseMulDiv());
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} else if (pos < src.length() && src.charAt(pos) == '-') {
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pos++;
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left = new CheckedSubtract(left, parseMulDiv());
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} else break;
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}
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return left;
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}
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private AbstractExpression parseMulDiv() {
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AbstractExpression left = parsePower();
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while (true) {
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skipWhitespace();
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if (pos < src.length() && src.charAt(pos) == '*' && nextCharIs('*')) {
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pos++;
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left = new CheckedMultiply(left, parsePower());
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} else if (pos < src.length() && src.charAt(pos) == '/' && nextCharIs('/')) {
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pos++;
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left = new CheckedDivide(left, parsePower());
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} else break;
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}
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return left;
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}
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private AbstractExpression parsePower() {
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AbstractExpression left = parseUnary();
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while (true) {
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skipWhitespace();
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if (pos + 1 < src.length() && src.charAt(pos) == '*' && src.charAt(pos + 1) == '*') {
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pos += 2;
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left = new Power(left, parseUnary());
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} else if (pos + 1 < src.length() && src.charAt(pos) == '/' && src.charAt(pos + 1) == '/') {
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pos += 2;
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left = new Log(left, parseUnary());
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} else break;
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}
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return left;
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}
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private AbstractExpression parseUnary() {
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skipWhitespace();
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if (pos >= src.length())
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throw new IllegalArgumentException("Unexpected end of expression at position " + pos);
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if (src.charAt(pos) == '-') {
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pos++;
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if (pos < src.length() && Character.isDigit(src.charAt(pos))) return parsePostfix(parseNumber(true));
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return new CheckedNegate(parseUnary());
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}
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// abs: ||x|| (U+2016 DOUBLE VERTICAL LINE)
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if (src.charAt(pos) == '‖') {
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pos++;
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AbstractExpression inner = parseMinMax();
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skipWhitespace();
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if (pos >= src.length() || src.charAt(pos) != '‖')
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throw new IllegalArgumentException("Expected ‖ at position " + pos);
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pos++;
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return parsePostfix(new Abs(inner));
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}
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// prefix unary: sqrt U+221A, cbrt U+221B
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if (src.charAt(pos) == '√') { pos++; return parsePostfix(new Sqrt(parseUnary())); }
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if (src.charAt(pos) == '∛') { pos++; return parsePostfix(new Cbrt(parseUnary())); }
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if (tryConsume("reverse")) return parsePostfix(new Reverse(parseUnary()));
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if (tryConsume("digits")) return parsePostfix(new Digits(parseUnary()));
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if (tryConsume("floor")) return parsePostfix(new Floor(parseUnary()));
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if (tryConsume("ceiling")) return parsePostfix(new Ceiling(parseUnary()));
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if (tryConsume("log₂") || tryConsume("log2")) return parsePostfix(new Log2(parseUnary()));
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if (tryConsume("pow₂") || tryConsume("pow2")) return parsePostfix(new Pow2(parseUnary()));
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if (tryConsume("low")) return parsePostfix(new Low(parseUnary()));
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if (tryConsume("high")) return parsePostfix(new High(parseUnary()));
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return parsePostfix(parsePrimary());
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}
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private AbstractExpression parsePostfix(AbstractExpression base) {
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skipWhitespace();
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if (pos < src.length() && src.charAt(pos) == '²') { pos++; return parsePostfix(new Square(base)); }
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if (pos < src.length() && src.charAt(pos) == '³') { pos++; return parsePostfix(new Cube(base)); }
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return base;
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}
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private AbstractExpression parsePrimary() {
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skipWhitespace();
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if (pos >= src.length()) throw new IllegalArgumentException("Unexpected end of expression");
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char c = src.charAt(pos);
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if (c == '(') {
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pos++;
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AbstractExpression inner = parseMinMax();
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skipWhitespace();
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expect();
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return inner;
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}
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if (c == '$') { pos++; return new Variable(parseIndex()); }
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if (Character.isDigit(c)) return parseNumber(false);
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if (Character.isLetter(c)) {
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int start = pos;
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while (pos < src.length() && (Character.isLetterOrDigit(src.charAt(pos)) || src.charAt(pos) == '_'))
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pos++;
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String name = src.substring(start, pos);
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int idx = variables != null ? variables.indexOf(name) : -1;
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if (idx >= 0) return new Variable(idx, name);
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throw new IllegalArgumentException("Unknown identifier '" + name + "' at position " + start);
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}
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throw new IllegalArgumentException("Unexpected character '" + c + "' at position " + pos);
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}
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private void skipWhitespace() {
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while (pos < src.length() && Character.isWhitespace(src.charAt(pos))) pos++;
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}
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private boolean nextCharIs(char next) {
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return pos + 1 >= src.length() || src.charAt(pos + 1) != next;
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}
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private boolean tryConsume(String keyword) {
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skipWhitespace();
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if (!src.startsWith(keyword, pos)) return false;
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int end = pos + keyword.length();
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if (end < src.length()) {
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char next = src.charAt(end);
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if (Character.isLetterOrDigit(next) || next == '_') return false;
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}
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if (variables != null && variables.contains(keyword)) return false;
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pos = end;
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return true;
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}
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private void expect() {
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if (pos >= src.length() || src.charAt(pos) != ')')
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throw new IllegalArgumentException("Expected '" + ')' + "' at position " + pos
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+ (pos < src.length() ? ", got '" + src.charAt(pos) + "'" : ", got end of input"));
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pos++;
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}
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private AbstractExpression parseNumber(boolean negative) {
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int start = pos;
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while (pos < src.length() && Character.isDigit(src.charAt(pos))) pos++;
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if (start == pos) throw new IllegalArgumentException("Expected digit at position " + pos);
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String numStr = src.substring(start, pos);
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int result = 0;
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for (int i = 0; i < numStr.length(); i++) {
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int digit = numStr.charAt(i) - '0';
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if (!negative) {
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if (result > (Integer.MAX_VALUE - digit) / 10)
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throw new OverflowException("constant " + numStr);
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result = result * 10 + digit;
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} else {
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if (result < (Integer.MIN_VALUE + digit) / 10)
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throw new OverflowException("constant -" + numStr);
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result = result * 10 - digit;
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}
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}
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return new Const(result);
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}
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private int parseIndex() {
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int start = pos;
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while (pos < src.length() && Character.isDigit(src.charAt(pos))) pos++;
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if (start == pos) throw new IllegalArgumentException("Expected digit after '$' at position " + pos);
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return Integer.parseInt(src.substring(start, pos));
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}
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}
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