Add modulus operator

slox/Interpreter.swift

@@ -395,6 +395,8 @@ class Interpreter {
                 return .int(leftNumber * rightNumber)
             case .slash:
                 return .int(leftNumber / rightNumber)
+            case .modulus:
+                return .int(leftNumber % rightNumber)
             case .greater:
                 return .boolean(leftNumber > rightNumber)
             case .greaterEqual:

slox/Parser.swift

@@ -404,7 +404,7 @@ struct Parser {
     //    equality       → comparison ( ( "!=" | "==" ) comparison )* ;
     //    comparison     → term ( ( ">" | ">=" | "<" | "<=" ) term )* ;
     //    term           → factor ( ( "-" | "+" ) factor )* ;
-    //    factor         → unary ( ( "/" | "*" ) unary )* ;
+    //    factor         → unary ( ( "/" | "*" | "%" ) unary )* ;
     //    unary          → ( "!" | "-" ) unary
     //                   | postfix ;
     //    postfix        → primary ( "(" arguments? ")" | "." IDENTIFIER | "[" logicOr "]" )* ;
@@ -503,7 +503,7 @@ struct Parser {
     mutating private func parseFactor() throws -> Expression {
         var expr = try parseUnary()
 
-        while currentTokenMatchesAny(types: [.slash, .star]) {
+        while currentTokenMatchesAny(types: [.slash, .star, .modulus]) {
             let oper = previousToken
             let rightExpr = try parseUnary()
             expr = .binary(expr, oper, rightExpr)

slox/Scanner.swift

@@ -82,6 +82,8 @@ struct Scanner {
             handleSingleCharacterLexeme(type: .semicolon)
         case "*":
             handleSingleCharacterLexeme(type: .star)
+        case "%":
+            handleSingleCharacterLexeme(type: .modulus)
         case "/":
             handleSlash()
 

slox/TokenType.swift

@@ -20,6 +20,7 @@ enum TokenType: Equatable {
     case star
     case leftBracket
     case rightBracket
+    case modulus
 
     // One of two character tokens
     case bang

sloxTests/InterpreterTests.swift

@@ -74,6 +74,14 @@ final class InterpreterTests: XCTestCase {
         XCTAssertEqual(actual, expected)
     }
 
+    func testInterpretBinaryExpressionInvolvingModulusOperator() throws {
+        let input = "8 % 3"
+        let interpreter = Interpreter()
+        let actual = try interpreter.interpretRepl(source: input)!
+        let expected: LoxValue = .int(2)
+        XCTAssertEqual(actual, expected)
+    }
+
     func testInterpretStringlyBinaryExpression() throws {
         let input = "\"forty\" + \"-two\""
         let interpreter = Interpreter()

sloxTests/ParserTests.swift

@@ -158,6 +158,27 @@ final class ParserTests: XCTestCase {
         XCTAssertEqual(actual, expected)
     }
 
+    func testParseFactorExpressionWithModulusOperator() throws {
+        let tokens: [Token] = [
+            Token(type: .int, lexeme: "5", line: 1),
+            Token(type: .modulus, lexeme: "%", line: 1),
+            Token(type: .int, lexeme: "3", line: 1),
+            Token(type: .semicolon, lexeme: ";", line: 1),
+            Token(type: .eof, lexeme: "", line: 1),
+        ]
+        var parser = Parser(tokens: tokens)
+
+        let actual = try parser.parse()
+        let expected: [Statement] = [
+            .expression(
+                .binary(
+                    .literal(.int(5)),
+                    Token(type: .modulus, lexeme: "%", line: 1),
+                    .literal(.int(3))))
+        ]
+        XCTAssertEqual(actual, expected)
+    }
+
     func testParseTermExpression() throws {
         let tokens: [Token] = [
             Token(type: .string, lexeme: "\"forty-\"", line: 1),

sloxTests/ScannerTests.swift

@@ -9,7 +9,7 @@ import XCTest
 
 final class ScannerTests: XCTestCase {
     func testScanningOfOneCharacterLexemes() throws {
-        let source = "( ) { } [ ] , . - + ; *"
+        let source = "( ) { } [ ] , . - + ; * %"
         var scanner = Scanner(source: source)
         let actual = try! scanner.scanTokens()
         let expected: [Token] = [
@@ -25,6 +25,7 @@ final class ScannerTests: XCTestCase {
             Token(type: .plus, lexeme: "+", line: 1),
             Token(type: .semicolon, lexeme: ";", line: 1),
             Token(type: .star, lexeme: "*", line: 1),
+            Token(type: .modulus, lexeme: "%", line: 1),
             Token(type: .eof, lexeme: "", line: 1),
         ]