A Toy Language Interpreter Ionuț G. Stan · BJUG #28 · December 2014 

Ionuț G. Stan · [email protected] · igstan.ro Plan ‣ Interpreters and Compilers ‣ Why Learn Compilers ‣ Why Scala for Today ‣ Coding Part 

Ionuț G. Stan · [email protected] · igstan.ro Interpreters and Compilers 

Ionuț G. Stan · [email protected] · igstan.ro Interpreters Interpreter Result Source 

Ionuț G. Stan · [email protected] · igstan.ro Interpreters Parser Interpreter Result Source 

Ionuț G. Stan · [email protected] · igstan.ro Interpreters Parser Interpreter Result Source AST (Abstract Syntax Tree) 

Ionuț G. Stan · [email protected] · igstan.ro Interpreters Lexer Parser Interpreter Result Source 

Ionuț G. Stan · [email protected] · igstan.ro Interpreters Lexer Parser Type Checker Interpreter Source Result 

Ionuț G. Stan · [email protected] · igstan.ro Compilers Compiler Target Source 

Ionuț G. Stan · [email protected] · igstan.ro Compilers Compiler Target Interpreter Result Source 

Ionuț G. Stan · [email protected] · igstan.ro Compilers Lexer Parser Type Checker Code Emitter Source Target 

Ionuț G. Stan · [email protected] · igstan.ro Many Other Phases Lexer Parser Type Checker Source Target ... 

Ionuț G. Stan · [email protected] · igstan.ro Today Parser Interpreter Result Source AST (Abstract Syntax Tree) 

Ionuț G. Stan · [email protected] · igstan.ro Why Learn Compilers 

Ionuț G. Stan · [email protected] · igstan.ro Why Learn Compilers ‣ This is my motivation ‣ I like looking under the hood ‣ A compiler's hood is like a starship's hood ‣ Compilers are really well documented ‣ You get to understand tricky language concepts ‣ You get to understand modular architecture ‣ Useful for (E)DSLs development ‣ It's fun! 

Ionuț G. Stan · [email protected] · igstan.ro Why Learn Compilers ‣ This is my motivation ‣ I like looking under the hood ‣ A compiler's hood is like a starship's hood ‣ Compilers are really well documented ‣ You get to understand tricky language concepts ‣ You get to understand modular architecture ‣ Useful for (E)DSLs development ‣ It's fun! 

Ionuț G. Stan · [email protected] · igstan.ro Why Learn Compilers ‣ This is my motivation ‣ I like looking under the hood ‣ A compiler's hood is like a starship's hood ‣ Compilers are really well documented ‣ You get to understand tricky language concepts ‣ You get to understand modular architecture ‣ Useful for (E)DSLs development ‣ It's fun! 

Ionuț G. Stan · [email protected] · igstan.ro Why Learn Compilers ‣ This is my motivation ‣ I like looking under the hood ‣ A compiler's hood is like a starship's hood ‣ Compilers are really well documented ‣ You get to understand tricky language concepts ‣ You get to understand modular architecture ‣ Useful for (E)DSLs development ‣ It's fun! 

Ionuț G. Stan · [email protected] · igstan.ro Why Learn Compilers ‣ This is my motivation ‣ I like looking under the hood ‣ A compiler's hood is like a starship's hood ‣ Compilers are really well documented ‣ You get to understand tricky language concepts ‣ You get to understand modular architecture ‣ Useful for (E)DSLs development ‣ It's fun! 

Ionuț G. Stan · [email protected] · igstan.ro Why Learn Compilers ‣ This is my motivation ‣ I like looking under the hood ‣ A compiler's hood is like a starship's hood ‣ Compilers are really well documented ‣ You get to understand tricky language concepts ‣ You get to understand modular architecture ‣ Useful for (E)DSLs development ‣ It's fun! 

Ionuț G. Stan · [email protected] · igstan.ro Why Learn Compilers ‣ This is my motivation ‣ I like looking under the hood ‣ A compiler's hood is like a starship's hood ‣ Compilers are really well documented ‣ You get to understand tricky language concepts ‣ You get to understand modular architecture ‣ Useful for (E)DSLs development ‣ It's fun! 

Ionuț G. Stan · [email protected] · igstan.ro Why Learn Compilers ‣ This is my motivation ‣ I like looking under the hood ‣ A compiler's hood is like a starship's hood ‣ Compilers are really well documented ‣ You get to understand tricky language concepts ‣ You get to understand modular architecture ‣ Useful for (E)DSLs development ‣ It's fun! 

Ionuț G. Stan · [email protected] · igstan.ro Why Scala 

Ionuț G. Stan · [email protected] · igstan.ro Why Scala ‣ I could have used Java 8 ‣ But... there's one missing feature in Java 8 ‣ The closest alternative is the Visitor pattern ‣ But that's a cumbersome pattern ‣ Last, but not least, I write Scala daily :-) 

Ionuț G. Stan · [email protected] · igstan.ro Why Scala ‣ I could have used Java 8 ‣ One missing feature, though ‣ The closest alternative is the Visitor pattern ‣ But that's a cumbersome pattern ‣ Last, but not least, I write Scala daily :-) 

Ionuț G. Stan · [email protected] · igstan.ro Why Scala ‣ I could have used Java 8 ‣ One missing feature, though: pattern matching ‣ The closest alternative is the Visitor pattern ‣ But that's a cumbersome pattern ‣ Last, but not least, I write Scala daily :-) 

Ionuț G. Stan · [email protected] · igstan.ro Representing an AST in Scala trait Node! case class Num(value: Int) extends Node! case class Add(left: Node, right: Node) extends Node! ! val ast = Add(Num(1), Num(2))! ! val sum = ast match {! case Add(Num(a), Num(b)) => a + b! } 

Ionuț G. Stan · [email protected] · igstan.ro Representing an AST in Scala trait Node! case class Num(value: Int) extends Node! case class Add(left: Node, right: Node) extends Node! ! val ast = Add(Num(1), Num(2))! ! val sum = ast match {! case Add(Num(a), Num(b)) => a + b! } 

Ionuț G. Stan · [email protected] · igstan.ro Representing an AST in Scala trait Node! case class Num(value: Int) extends Node! case class Add(left: Node, right: Node) extends Node! ! val ast = Add(Num(1), Num(2))! ! val sum = ast match {! case Add(Num(a), Num(b)) => a + b! } 

Ionuț G. Stan · [email protected] · igstan.ro Representing an AST in Scala trait Node! case class Num(value: Int) extends Node! case class Add(left: Node, right: Node) extends Node! ! val ast = Add(Num(1), Num(2))! ! val sum = ast match {! case Add(Num(a), Num(b)) => a + b! } 

Ionuț G. Stan · [email protected] · igstan.ro Traversing an AST in Scala trait Node! case class Num(value: Int) extends Node! case class Add(left: Node, right: Node) extends Node! ! val ast = Add(Num(1), Num(2))! ! val sum = ast match {! case Add(Num(a), Num(b)) => a + b! } 

Ionuț G. Stan · [email protected] · igstan.ro Why Scala ‣ I could have used Java 8 ‣ One missing feature, though: pattern matching ‣ The closest alternative is the Visitor pattern ‣ But that's a cumbersome pattern ‣ Last, but not least, I write Scala daily :-) 

Ionuț G. Stan · [email protected] · igstan.ro Representing an AST in Java public interface Node {}! ! public class Num implements Node {! public final int value;! public Num(int value) { this.value = value; }! }! ! public class Add implements Node {! public final Node left, right;! public Add(Node left, Node right) {! this.left = left;! this.right = right;! }! } 

Ionuț G. Stan · [email protected] · igstan.ro Representing an AST in Java public interface Node {}! ! public class Num implements Node {! public final int value;! public Num(int value) { this.value = value; }! }! ! public class Add implements Node {! public final Node left, right;! public Add(Node left, Node right) {! this.left = left;! this.right = right;! }! } 

Ionuț G. Stan · [email protected] · igstan.ro Representing an AST in Java public interface Node {}! ! public class Num implements Node {! public final int value;! public Num(int value) { this.value = value; }! }! ! public class Add implements Node {! public final Node left, right;! public Add(Node left, Node right) {! this.left = left;! this.right = right;! }! } 

Ionuț G. Stan · [email protected] · igstan.ro Traversing an AST in Java public interface Node {! public R match(Matcher matcher);! }! ! public interface Matcher {! public R matchNum(Num n);! public R matchAdd(Add a);! } 

Ionuț G. Stan · [email protected] · igstan.ro Traversing an AST in Java public class Num implements Node {! // fields and constructor omitted! ! @Override! public R match(Matcher matcher) {! return matcher.matchNum(this);! }! } 

Ionuț G. Stan · [email protected] · igstan.ro Traversing an AST in Java public class Add implements Node {! // fields and constructor omitted! ! @Override! public R match(Matcher matcher) {! return matcher.matchAdd(this);! }! } 

Ionuț G. Stan · [email protected] · igstan.ro Traversing an AST in Java int ast = new Add(new Num(1), new Num(2));! ! int sum = ast.match(new Matcher {! @Override! public R matchNum(Num n) {! return n.value;! }! ! @Override! public R matchAdd(Add a) {! int left = a.left.match(this);! int right = a.right.match(this);! return left + right;! }! }); 

Ionuț G. Stan · [email protected] · igstan.ro Traversing an AST in Java int ast = new Add(new Num(1), new Num(2));! ! int sum = ast.match(new Matcher {! @Override! public R matchNum(Num n) {! return n.value;! }! ! @Override! public R matchAdd(Add a) {! int left = a.left.match(this);! int right = a.right.match(this);! return left + right;! }! }); 

Ionuț G. Stan · [email protected] · igstan.ro Traversing an AST in Java int ast = new Add(new Num(1), new Num(2));! ! int sum = ast.match(new Matcher {! @Override! public Integer matchNum(Num n) {! return n.value;! }! ! @Override! public R matchAdd(Add a) {! int left = a.left.match(this);! int right = a.right.match(this);! return left + right;! }! }); 

Ionuț G. Stan · [email protected] · igstan.ro Traversing an AST in Java int ast = new Add(new Num(1), new Num(2));! ! int sum = ast.match(new Matcher {! @Override! public Integer matchNum(Num n) {! return n.value;! }! ! @Override! public Integer matchAdd(Add a) {! int left = a.left.match(this);! int right = a.right.match(this);! return left + right;! }! }); 

Ionuț G. Stan · [email protected] · igstan.ro Traversing an AST in Java public interface Node {! public R match(Matcher matcher);! }! ! public interface Matcher {! public R matchNum(Num n);! public R matchAdd(Add a);! } 

Ionuț G. Stan · [email protected] · igstan.ro The Visitor Pattern public interface Node {! public R visit(NodeVisitor visitor);! }! ! public interface NodeVisitor {! public R visitNum(Num n);! public R visitAdd(Add a);! } 

Ionuț G. Stan · [email protected] · igstan.ro Nashorn $ nashorn: cd nashorn/src/jdk/nashorn/internal/ir/! $ ir: ls *Node.java! AccessNode.java FunctionNode.java ReturnNode.java! BaseNode.java IdentNode.java RuntimeNode.java! BinaryNode.java IfNode.java SplitNode.java! BreakNode.java IndexNode.java SwitchNode.java! BreakableNode.java LabelNode.java TernaryNode.java! CallNode.java LexicalContextNode.java ThrowNode.java! CaseNode.java LiteralNode.java TryNode.java! CatchNode.java LoopNode.java UnaryNode.java! ContinueNode.java Node.java VarNode.java! EmptyNode.java ObjectNode.java WhileNode.java! ForNode.java PropertyNode.java WithNode.java 

Ionuț G. Stan · [email protected] · igstan.ro Nashorn $ ir: cd ..! $ internal: find . -name *Visitor*! ./ir/debug/PrintVisitor.java! ./ir/visitor/NodeOperatorVisitor.java! ./ir/visitor/NodeVisitor.java! $ internal: grep -hR 'extends NodeVisitor' .! final class FoldConstants extends NodeVisitor {! final class Splitter extends NodeVisitor {! public final class JSONWriter extends NodeVisitor {! public final class PrintVisitor extends NodeVisitor {! public class NodeOperatorVisitor extends NodeVisitor { 

Ionuț G. Stan · [email protected] · igstan.ro Example Interpreter in Java https://github.com/igstan/tree-interpreter-visitor 

Ionuț G. Stan · [email protected] · igstan.ro Why Scala ‣ I could have used Java 8 ‣ One missing feature, though: pattern matching ‣ The closest alternative is the Visitor pattern ‣ Cumbersome pattern, for me ‣ Last, but not least, I write Scala daily :-) 

Ionuț G. Stan · [email protected] · igstan.ro Why Scala ‣ I could have used Java 8 ‣ One missing feature, though: pattern matching ‣ The closest alternative is the Visitor pattern ‣ Cumbersome pattern, for me ‣ Last, but not least, I write Scala daily :-) 

Ionuț G. Stan · [email protected] · igstan.ro Why Scala ‣ I could have used Java 8 ‣ One missing feature, though: pattern matching ‣ The closest alternative is the Visitor pattern ‣ Cumbersome pattern, for me ‣ Last, but not least, I write Scala daily :-) 

Ionuț G. Stan · [email protected] · igstan.ro Coding Part