Implement functions and lambdas

slox.xcodeproj/project.pbxproj

@@ -7,6 +7,8 @@
 	objects = {
 
 /* Begin PBXBuildFile section */
+		8732838F2B93F89300E49035 /* NativeFunction.swift in Sources */ = {isa = PBXBuildFile; fileRef = 8732838E2B93F89300E49035 /* NativeFunction.swift */; };
+		873283902B93FC0900E49035 /* NativeFunction.swift in Sources */ = {isa = PBXBuildFile; fileRef = 8732838E2B93F89300E49035 /* NativeFunction.swift */; };
 		873CCB212B8D5FAE00FC249A /* Interpreter.swift in Sources */ = {isa = PBXBuildFile; fileRef = 873CCB202B8D5FAE00FC249A /* Interpreter.swift */; };
 		873CCB232B8D617C00FC249A /* RuntimeError.swift in Sources */ = {isa = PBXBuildFile; fileRef = 873CCB222B8D617C00FC249A /* RuntimeError.swift */; };
 		873CCB252B8D765D00FC249A /* Lox.swift in Sources */ = {isa = PBXBuildFile; fileRef = 873CCB242B8D765D00FC249A /* Lox.swift */; };
@@ -21,6 +23,8 @@
 		873CCB312B8EBB7800FC249A /* Statement.swift in Sources */ = {isa = PBXBuildFile; fileRef = 873CCB2F2B8EAEC100FC249A /* Statement.swift */; };
 		873CCB332B8ED8B900FC249A /* Environment.swift in Sources */ = {isa = PBXBuildFile; fileRef = 873CCB322B8ED8B900FC249A /* Environment.swift */; };
 		873CCB342B8EE0FF00FC249A /* Environment.swift in Sources */ = {isa = PBXBuildFile; fileRef = 873CCB322B8ED8B900FC249A /* Environment.swift */; };
+		8755B8B42B91983F00530DC4 /* UserDefinedFunction.swift in Sources */ = {isa = PBXBuildFile; fileRef = 87BAFC4A2B918C520013E5FE /* UserDefinedFunction.swift */; };
+		8755B8B52B91984C00530DC4 /* LoxCallable.swift in Sources */ = {isa = PBXBuildFile; fileRef = 87BAFC482B9179CB0013E5FE /* LoxCallable.swift */; };
 		876560032B882259002BDE42 /* TokenType.swift in Sources */ = {isa = PBXBuildFile; fileRef = 876560022B882259002BDE42 /* TokenType.swift */; };
 		876560052B8825AC002BDE42 /* Token.swift in Sources */ = {isa = PBXBuildFile; fileRef = 876560042B8825AC002BDE42 /* Token.swift */; };
 		876560072B8827F9002BDE42 /* Scanner.swift in Sources */ = {isa = PBXBuildFile; fileRef = 876560062B8827F9002BDE42 /* Scanner.swift */; };
@@ -35,6 +39,10 @@
 		876A31652B8C04990085A350 /* Expression.swift in Sources */ = {isa = PBXBuildFile; fileRef = 876A31642B8C04990085A350 /* Expression.swift */; };
 		876A31672B8C11810085A350 /* Parser.swift in Sources */ = {isa = PBXBuildFile; fileRef = 876A31662B8C11810085A350 /* Parser.swift */; };
 		876A31692B8C3AAB0085A350 /* ParseError.swift in Sources */ = {isa = PBXBuildFile; fileRef = 876A31682B8C3AAB0085A350 /* ParseError.swift */; };
+		877168C22B91A9BD00723543 /* Return.swift in Sources */ = {isa = PBXBuildFile; fileRef = 877168C12B91A9BD00723543 /* Return.swift */; };
+		87BAFC492B9179CB0013E5FE /* LoxCallable.swift in Sources */ = {isa = PBXBuildFile; fileRef = 87BAFC482B9179CB0013E5FE /* LoxCallable.swift */; };
+		87BAFC4B2B918C520013E5FE /* UserDefinedFunction.swift in Sources */ = {isa = PBXBuildFile; fileRef = 87BAFC4A2B918C520013E5FE /* UserDefinedFunction.swift */; };
+		87C2F3742B91C2BA00126707 /* Return.swift in Sources */ = {isa = PBXBuildFile; fileRef = 877168C12B91A9BD00723543 /* Return.swift */; };
 /* End PBXBuildFile section */
 
 /* Begin PBXCopyFilesBuildPhase section */
@@ -50,6 +58,7 @@
 /* End PBXCopyFilesBuildPhase section */
 
 /* Begin PBXFileReference section */
+		8732838E2B93F89300E49035 /* NativeFunction.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = NativeFunction.swift; sourceTree = "<group>"; };
 		873CCB202B8D5FAE00FC249A /* Interpreter.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Interpreter.swift; sourceTree = "<group>"; };
 		873CCB222B8D617C00FC249A /* RuntimeError.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = RuntimeError.swift; sourceTree = "<group>"; };
 		873CCB242B8D765D00FC249A /* Lox.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Lox.swift; sourceTree = "<group>"; };
@@ -68,6 +77,9 @@
 		876A31642B8C04990085A350 /* Expression.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Expression.swift; sourceTree = "<group>"; };
 		876A31662B8C11810085A350 /* Parser.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Parser.swift; sourceTree = "<group>"; };
 		876A31682B8C3AAB0085A350 /* ParseError.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ParseError.swift; sourceTree = "<group>"; };
+		877168C12B91A9BD00723543 /* Return.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Return.swift; sourceTree = "<group>"; };
+		87BAFC482B9179CB0013E5FE /* LoxCallable.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = LoxCallable.swift; sourceTree = "<group>"; };
+		87BAFC4A2B918C520013E5FE /* UserDefinedFunction.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = UserDefinedFunction.swift; sourceTree = "<group>"; };
 /* End PBXFileReference section */
 
 /* Begin PBXFrameworksBuildPhase section */
@@ -112,16 +124,20 @@
 				873CCB322B8ED8B900FC249A /* Environment.swift */,
 				876A31642B8C04990085A350 /* Expression.swift */,
 				873CCB202B8D5FAE00FC249A /* Interpreter.swift */,
-				876A315E2B897EEB0085A350 /* LoxValue.swift */,
 				873CCB242B8D765D00FC249A /* Lox.swift */,
+				87BAFC482B9179CB0013E5FE /* LoxCallable.swift */,
+				876A315E2B897EEB0085A350 /* LoxValue.swift */,
+				8732838E2B93F89300E49035 /* NativeFunction.swift */,
 				876A31682B8C3AAB0085A350 /* ParseError.swift */,
 				876A31662B8C11810085A350 /* Parser.swift */,
+				877168C12B91A9BD00723543 /* Return.swift */,
 				873CCB222B8D617C00FC249A /* RuntimeError.swift */,
 				876A31612B8986630085A350 /* ScanError.swift */,
 				876560062B8827F9002BDE42 /* Scanner.swift */,
 				873CCB2F2B8EAEC100FC249A /* Statement.swift */,
 				876560042B8825AC002BDE42 /* Token.swift */,
 				876560022B882259002BDE42 /* TokenType.swift */,
+				87BAFC4A2B918C520013E5FE /* UserDefinedFunction.swift */,
 			);
 			path = slox;
 			sourceTree = "<group>";
@@ -230,12 +246,16 @@
 				876A315F2B897EEB0085A350 /* LoxValue.swift in Sources */,
 				873CCB302B8EAEC100FC249A /* Statement.swift in Sources */,
 				873CCB232B8D617C00FC249A /* RuntimeError.swift in Sources */,
+				87BAFC492B9179CB0013E5FE /* LoxCallable.swift in Sources */,
 				873CCB212B8D5FAE00FC249A /* Interpreter.swift in Sources */,
+				877168C22B91A9BD00723543 /* Return.swift in Sources */,
 				876A31672B8C11810085A350 /* Parser.swift in Sources */,
 				876560072B8827F9002BDE42 /* Scanner.swift in Sources */,
+				87BAFC4B2B918C520013E5FE /* UserDefinedFunction.swift in Sources */,
 				873CCB332B8ED8B900FC249A /* Environment.swift in Sources */,
 				876A31652B8C04990085A350 /* Expression.swift in Sources */,
 				876560032B882259002BDE42 /* TokenType.swift in Sources */,
+				8732838F2B93F89300E49035 /* NativeFunction.swift in Sources */,
 				876A31692B8C3AAB0085A350 /* ParseError.swift in Sources */,
 				873CCB252B8D765D00FC249A /* Lox.swift in Sources */,
 			);
@@ -250,10 +270,14 @@
 				873CCB2C2B8E88A500FC249A /* InterpreterTests.swift in Sources */,
 				873CCB2E2B8E88D200FC249A /* RuntimeError.swift in Sources */,
 				873CCB342B8EE0FF00FC249A /* Environment.swift in Sources */,
+				8755B8B42B91983F00530DC4 /* UserDefinedFunction.swift in Sources */,
 				876A315C2B897C000085A350 /* Token.swift in Sources */,
 				876A31572B8979BD0085A350 /* ScannerTests.swift in Sources */,
 				876A31602B89827B0085A350 /* LoxValue.swift in Sources */,
 				873CCB312B8EBB7800FC249A /* Statement.swift in Sources */,
+				8755B8B52B91984C00530DC4 /* LoxCallable.swift in Sources */,
+				873283902B93FC0900E49035 /* NativeFunction.swift in Sources */,
+				87C2F3742B91C2BA00126707 /* Return.swift in Sources */,
 				873CCB282B8E7B6300FC249A /* Parser.swift in Sources */,
 				873CCB272B8E7AD100FC249A /* ParserTests.swift in Sources */,
 				876A315D2B897C020085A350 /* Scanner.swift in Sources */,

slox/Environment.swift

@@ -5,7 +5,7 @@
 //  Created by Danielle Kefford on 2/27/24.
 //
 
-class Environment {
+class Environment: Equatable {
     private var enclosingEnvironment: Environment?
     private var values: [String: LoxValue] = [:]
 
@@ -42,4 +42,8 @@ class Environment {
 
         throw RuntimeError.undefinedVariable(name)
     }
+
+    static func == (lhs: Environment, rhs: Environment) -> Bool {
+        return lhs === rhs
+    }
 }

slox/Expression.swift

@@ -13,4 +13,6 @@ indirect enum Expression: Equatable {
     case variable(Token)
     case assignment(Token, Expression)
     case logical(Expression, Token, Expression)
+    case call(Expression, Token, [Expression])
+    case lambda([Token], [Statement])
 }

slox/Interpreter.swift

@@ -5,30 +5,41 @@
 //  Created by Danielle Kefford on 2/26/24.
 //
 
-struct Interpreter {
+import Foundation
+
+class Interpreter {
     var environment: Environment = Environment()
 
-    mutating func interpret(statements: [Statement]) throws {
+    init() {
+        setUpGlobals()
+    }
+
+    private func setUpGlobals() {
+        for nativeFunction in NativeFunction.allCases {
+            environment.define(name: String(describing: nativeFunction),
+                               value: .nativeFunction(nativeFunction))
+        }
+    }
+
+    func interpret(statements: [Statement]) throws {
         for statement in statements {
             try execute(statement: statement)
         }
     }
 
-    mutating func interpretRepl(statements: [Statement]) throws -> LoxValue? {
-        var result: LoxValue? = nil
-
+    func interpretRepl(statements: [Statement]) throws -> LoxValue? {
         for (i, statement) in statements.enumerated() {
             if i == statements.endIndex-1, case .expression(let expr) = statement {
-                result = try evaluate(expr: expr)
+                return try evaluate(expr: expr)
             } else {
                 try execute(statement: statement)
             }
         }
 
-        return result
+        return nil
     }
 
-    mutating private func execute(statement: Statement) throws {
+    private func execute(statement: Statement) throws {
         switch statement {
         case .expression(let expr):
             let _ = try evaluate(expr: expr)
@@ -45,10 +56,14 @@ struct Interpreter {
                             environment: Environment(enclosingEnvironment: environment))
         case .while(let expr, let stmt):
             try handleWhileStatement(expr: expr, stmt: stmt)
+        case .function(let name, let lambda):
+            try handleFunctionDeclaration(name: name, lambda: lambda)
+        case .return(let returnToken, let expr):
+            try handleReturnStatement(returnToken: returnToken, expr: expr)
         }
     }
 
-    mutating private func handleIfStatement(testExpr: Expression,
+    private func handleIfStatement(testExpr: Expression,
                                    consequentStmt: Statement,
                                    alternativeStmt: Statement?) throws {
         if isTruthy(value: try evaluate(expr: testExpr)) {
@@ -63,6 +78,28 @@ struct Interpreter {
         print(literal)
     }
 
+    private func handleFunctionDeclaration(name: Token, lambda: Expression) throws {
+        guard case .lambda(let params, let body) = lambda else {
+            throw RuntimeError.notALambda
+        }
+
+        let environmentWhenDeclared = self.environment
+        let function = UserDefinedFunction(name: name.lexeme,
+                                   params: params,
+                                   enclosingEnvironment: environmentWhenDeclared,
+                                   body: body)
+        environment.define(name: name.lexeme, value: .userDefinedFunction(function))
+    }
+
+    private func handleReturnStatement(returnToken: Token, expr: Expression?) throws {
+        var value: LoxValue = .nil
+        if let expr {
+            value = try evaluate(expr: expr)
+        }
+
+        throw Return.return(value)
+    }
+
     private func handleVariableDeclaration(name: Token, expr: Expression?) throws {
         var value: LoxValue = .nil
         if let expr = expr {
@@ -72,18 +109,23 @@ struct Interpreter {
         environment.define(name: name.lexeme, value: value)
     }
 
-    mutating private func handleBlock(statements: [Statement], environment: Environment) throws {
+    func handleBlock(statements: [Statement], environment: Environment) throws {
         let environmentBeforeBlock = self.environment
-
         self.environment = environment
+
+        // This ensures that the previous environment is restored
+        // if the try below throws, which is what will happen if
+        // there is a return statement.
+        defer {
+            self.environment = environmentBeforeBlock
+        }
+
         for statement in statements {
             try execute(statement: statement)
         }
-
-        self.environment = environmentBeforeBlock
     }
 
-    mutating private func handleWhileStatement(expr: Expression, stmt: Statement) throws {
+    private func handleWhileStatement(expr: Expression, stmt: Statement) throws {
         while isTruthy(value: try evaluate(expr: expr)) {
             try execute(statement: stmt)
         }
@@ -105,6 +147,10 @@ struct Interpreter {
             return try handleAssignmentExpression(name: varToken, expr: valueExpr)
         case .logical(let leftExpr, let oper, let rightExpr):
             return try handleLogicalExpression(leftExpr: leftExpr, oper: oper, rightExpr: rightExpr)
+        case .call(let calleeExpr, let rightParen, let args):
+            return try handleFunctionCallExpression(calleeExpr: calleeExpr, rightParen: rightParen, args: args)
+        case .lambda(let params, let statements):
+            return try handleLambdaExpression(params: params, statements: statements)
         }
     }
 
@@ -175,7 +221,7 @@ struct Interpreter {
         }
     }
 
-    func handleAssignmentExpression(name: Token, expr: Expression) throws -> LoxValue {
+    private func handleAssignmentExpression(name: Token, expr: Expression) throws -> LoxValue {
         let value = try evaluate(expr: expr)
         try environment.assign(name: name.lexeme, value: value)
         return value
@@ -201,6 +247,44 @@ struct Interpreter {
         }
     }
 
+    private func handleFunctionCallExpression(calleeExpr: Expression,
+                                              rightParen: Token,
+                                              args: [Expression]) throws -> LoxValue {
+        let callee = try evaluate(expr: calleeExpr)
+
+        let actualFunction: LoxCallable = switch callee {
+        case .userDefinedFunction(let userDefinedFunction):
+            userDefinedFunction
+        case .nativeFunction(let nativeFunction):
+            nativeFunction
+        default:
+            throw RuntimeError.notAFunction
+        }
+
+        guard args.count == actualFunction.arity else {
+            throw RuntimeError.wrongArity(actualFunction.arity, args.count)
+        }
+
+        var argValues: [LoxValue] = []
+        for arg in args {
+            let argValue = try evaluate(expr: arg)
+            argValues.append(argValue)
+        }
+
+        return try actualFunction.call(interpreter: self, args: argValues)
+    }
+
+    private func handleLambdaExpression(params: [Token], statements: [Statement]) throws -> LoxValue {
+        let environmentWhenDeclared = self.environment
+
+        let function = UserDefinedFunction(name: "<lambda>",
+                                   params: params,
+                                   enclosingEnvironment: environmentWhenDeclared,
+                                   body: statements)
+
+        return .userDefinedFunction(function)
+    }
+
     private func isEqual(leftValue: LoxValue, rightValue: LoxValue) -> Bool {
         switch (leftValue, rightValue) {
         case (.nil, .nil):

slox/LoxCallable.swift

@@ -0,0 +1,11 @@
+//
+//  Callable.swift
+//  slox
+//
+//  Created by Danielle Kefford on 2/29/24.
+//
+
+protocol LoxCallable {
+    var arity: Int { get }
+    func call(interpreter: Interpreter, args: [LoxValue]) throws -> LoxValue
+}

slox/LoxValue.swift

@@ -1,5 +1,5 @@
 //
-//  Literal.swift
+//  LoxValue.swift
 //  slox
 //
 //  Created by Danielle Kefford on 2/23/24.
@@ -10,6 +10,8 @@ enum LoxValue: CustomStringConvertible, Equatable {
     case number(Double)
     case boolean(Bool)
     case `nil`
+    case userDefinedFunction(UserDefinedFunction)
+    case nativeFunction(NativeFunction)
 
     var description: String {
         switch self {
@@ -21,6 +23,10 @@ enum LoxValue: CustomStringConvertible, Equatable {
             return "\(boolean)"
         case .nil:
             return "nil"
+        case .userDefinedFunction(let function):
+            return "<function: \(function.name)>"
+        case .nativeFunction(let function):
+            return "<function: \(function)>"
         }
     }
 }

slox/NativeFunction.swift

@@ -0,0 +1,26 @@
+//
+//  NativeFunction.swift
+//  slox
+//
+//  Created by Danielle Kefford on 3/2/24.
+//
+
+import Foundation
+
+enum NativeFunction: LoxCallable, Equatable, CaseIterable {
+    case clock
+
+    var arity: Int {
+        switch self {
+        case .clock:
+            return 0
+        }
+    }
+
+    func call(interpreter: Interpreter, args: [LoxValue]) throws -> LoxValue {
+        switch self {
+        case .clock:
+            return .number(Date().timeIntervalSince1970)
+        }
+    }
+}