function checkJaneSyntax(code) {
    let errors = [];
    let lines = code.split("\n");
    let variables = new Set();

    let assignmentRegex = /^\s*var\s+([a-zA-Z][a-zA-Z0-9]*)\s*;?\s*$/;
    let valueAssignmentRegex = /^\s*([a-zA-Z][a-zA-Z0-9]*)\s*:=\s*[0-9a-zA-Z+\-*\/]+\s*;?\s*$/;
    let ifRegex = /^\s*if\s*\(.+\)\s*then\s*\{.*\}\s*;?\s*$/;
    let whileRegex = /^\s*while\s*\(.+\)\s*do\s*\{.*\}\s*;?\s*$/;

    for (let i = 0; i < lines.length; i++) {
        let line = lines[i].trim();
        if (!line) continue;

        if (assignmentRegex.test(line)) {
            let varName = line.match(assignmentRegex)[1];
            if (variables.has(varName)) {
                errors.push(`Error on line ${i + 1}: variable '${varName}' is already declared.`);
            } else {
                variables.add(varName);
            }
            if (!line.endsWith(";")) {
                errors.push(`Error on line ${i + 1}: Missing semicolon at the end of the line.`);
            }
        } else if (valueAssignmentRegex.test(line)) {
            let varName = line.match(valueAssignmentRegex)[1];
            if (!variables.has(varName)) {
                errors.push(`Error on line ${i + 1}: variable '${varName}' is not declared.`);
            }
            if (!line.endsWith(";")) {
                errors.push(`Error on line ${i + 1}: Missing semicolon at the end of the line.`);
            }
        } else if (ifRegex.test(line)) {
            if (!line.endsWith(";")) {
                errors.push(`Error on line ${i + 1}: Missing semicolon at the end of the line.`);
            }
        } else if (whileRegex.test(line)) {
            if (!line.endsWith(";")) {
                errors.push(`Error on line ${i + 1}: Missing semicolon at the end of the line.`);
            }
        } else {
            errors.push(`Error on line ${i + 1}: invalid syntax.`);
        }
    }

    return errors.length ? errors : ["Syntax is correct!"];
}