While loop

Sources/Lox/AbstractSyntaxTreePrinter.swift

@@ -74,6 +74,10 @@ public struct AbstractSyntaxTreePrinter: StatementVisitor, ExpressionVisitor {
     public func visit(_ expr: Variable) -> String {
         expr.name.lexeme
     }
+
+    public func visit(_ stmt: While) -> String {
+        parenthesize(name: "while", parts: stmt.condition, stmt.body)
+    }
 }
 
 extension AbstractSyntaxTreePrinter {

Sources/Lox/Definitions/Statement.swift

@@ -17,6 +17,7 @@ public protocol StatementVisitor {
     func visit(_ stmt: If) -> StatementVisitorReturn
     func visit(_ stmt: Block) -> StatementVisitorReturn
     func visit(_ stmt: Var) -> StatementVisitorReturn
+    func visit(_ stmt: While) -> StatementVisitorReturn
     func visit(_ stmt: Print) -> StatementVisitorReturn
 }
 
@@ -74,6 +75,20 @@ public struct Var: Statement {
     }
 }
 
+public struct While: Statement {
+    let condition: Expression
+    let body: Statement
+
+    init(condition: Expression, body: Statement) {
+        self.condition = condition
+        self.body = body
+    }
+
+    public func accept<V: StatementVisitor, R>(visitor: V) -> R where R == V.StatementVisitorReturn {
+        return visitor.visit(self)
+    }
+}
+
 public struct Print: Statement {
     let expression: Expression
 

Sources/Lox/Interpreter.swift

@@ -12,7 +12,7 @@ public final class Interpreter: StatementVisitor, ExpressionVisitor {
 
     func interpret(_ statements: Array<Statement>) {
         for statement in statements {
-            let result = execute(stmt: statement)
+            let result = execute(statement)
             if case let .failure(error) = result {
                 Lox.reportError(error)
             }
@@ -43,9 +43,9 @@ public final class Interpreter: StatementVisitor, ExpressionVisitor {
 
     public func visit(_ stmt: If) -> Value? {
         if determineTruthy(evaluate(stmt.condition)) {
-            execute(stmt: stmt.then)
+            execute(stmt.then)
         } else if let `else` = stmt.else {
-            execute(stmt: `else`)
+            execute(`else`)
         }
 
         return nil
@@ -260,14 +260,21 @@ public final class Interpreter: StatementVisitor, ExpressionVisitor {
         }
     }
 
+    public func visit(_ stmt: While) -> Value? {
+        while determineTruthy(evaluate(stmt.condition)) {
+            execute(stmt.body)
+        }
+        return nil
+    }
+
     public typealias Value = Result<Any, InterpreterError>
     public typealias ExpressionVisitorReturn = Value?
     public typealias StatementVisitorReturn = Value?
 }
 
 extension Interpreter {
     @discardableResult
-    private func execute(stmt: Statement) -> Value? {
+    private func execute(_ stmt: Statement) -> Value? {
         let value = stmt.accept(visitor: self)
         return value
     }
@@ -281,7 +288,7 @@ extension Interpreter {
         }
 
         for statement in statements {
-            let result = execute(stmt: statement)
+            let result = execute(statement)
             if case let .failure(error) = result {
                 return .failure(error)
             }

Sources/Lox/Parser.swift

@@ -58,13 +58,28 @@ public class Parser {
     private func statement() throws -> Statement {
         if match(.if) { return try ifStatement() }
         if match(.print) { return try printStatement() }
+        if match(.while) { return try whileStatement() }
         if match(.leftBrace) {
             return Block(statements: try block())
         }
 
         return try expressionStatement()
     }
 
+    private func whileStatement() throws -> Statement {
+        do { try consume(.leftParenthesis) }
+        catch { throw reportError("Expect '(' after 'while'.", token: latestToken) }
+
+        let condition = try expression()
+
+        do { try consume(.rightParenthesis) }
+        catch { throw reportError("Expect ')' after condition.", token: latestToken) }
+
+        let body = try statement()
+
+        return While(condition: condition, body: body)
+    }
+
     private func variableDeclaration() throws -> Statement {
         let name: Token
         do { name = try consume(.identifier) }

Sources/SyntaxDefinitionGenerator/Resources/statement.json

@@ -19,6 +19,10 @@
       "name": "Var",
       "parameterField": "name: Token, initializer: Expression?"
     },
+    {
+      "name": "While",
+      "parameterField": "condition: Expression, body: Statement"
+    },
     {
       "name": "Print",
       "parameterField": "expression: Expression"