Restructure AST to make roles more clear.

src/main/kotlin/gay/pizza/pork/ast/Define.kt

@@ -1,8 +0,0 @@
-package gay.pizza.pork.ast
-
-class Define(val symbol: Symbol, val value: Expression) : Expression() {
-  override val type: NodeType = NodeType.Define
-
-  override fun <T> visitChildren(visitor: Visitor<T>): List<T> =
-    visitor.visitNodes(symbol, value)
-}

src/main/kotlin/gay/pizza/pork/ast/ListLiteral.kt

@@ -1,8 +0,0 @@
-package gay.pizza.pork.ast
-
-class ListLiteral(val items: List<Expression>) : Expression() {
-  override val type: NodeType = NodeType.ListLiteral
-
-  override fun <T> visitChildren(visitor: Visitor<T>): List<T> =
-    visitor.visitAll(items)
-}

src/main/kotlin/gay/pizza/pork/ast/Node.kt

@@ -1,8 +0,0 @@
-package gay.pizza.pork.ast
-
-abstract class Node {
-  abstract val type: NodeType
-  open fun <T> visitChildren(visitor: Visitor<T>): List<T> = emptyList()
-
-  override fun toString(): String = let { node -> buildString { Printer(this).visit(node) } }
-}

src/main/kotlin/gay/pizza/pork/ast/NodeCoalescer.kt

@@ -0,0 +1,19 @@
+package gay.pizza.pork.ast
+
+import gay.pizza.pork.ast.nodes.*
+
+class NodeCoalescer(val handler: (Node) -> Unit) : NodeVisitor<Unit> {
+  override fun visitDefine(node: Define) = handler(node)
+  override fun visitFunctionCall(node: FunctionCall) = handler(node)
+  override fun visitReference(node: SymbolReference) = handler(node)
+  override fun visitIf(node: If) = handler(node)
+  override fun visitSymbol(node: Symbol) = handler(node)
+  override fun visitLambda(node: Lambda) = handler(node)
+  override fun visitIntLiteral(node: IntLiteral) = handler(node)
+  override fun visitBooleanLiteral(node: BooleanLiteral) = handler(node)
+  override fun visitListLiteral(node: ListLiteral) = handler(node)
+  override fun visitParentheses(node: Parentheses) = handler(node)
+  override fun visitPrefixOperation(node: PrefixOperation) = handler(node)
+  override fun visitInfixOperation(node: InfixOperation) = handler(node)
+  override fun visitProgram(node: Program) = handler(node)
+}

src/main/kotlin/gay/pizza/pork/ast/NodeVisitor.kt

@@ -1,6 +1,8 @@
 package gay.pizza.pork.ast
 
-interface Visitor<T> {
+import gay.pizza.pork.ast.nodes.*
+
+interface NodeVisitor<T> {
   fun visitDefine(node: Define): T
   fun visitFunctionCall(node: FunctionCall): T
   fun visitReference(node: SymbolReference): T

src/main/kotlin/gay/pizza/pork/ast/Parentheses.kt

@@ -1,8 +0,0 @@
-package gay.pizza.pork.ast
-
-class Parentheses(val expression: Expression) : Expression() {
-  override val type: NodeType = NodeType.Parentheses
-
-  override fun <T> visitChildren(visitor: Visitor<T>): List<T> =
-    visitor.visitNodes(expression)
-}

src/main/kotlin/gay/pizza/pork/ast/Printer.kt

@@ -1,6 +1,8 @@
 package gay.pizza.pork.ast
 
-class Printer(private val buffer: StringBuilder) : Visitor<Unit> {
+import gay.pizza.pork.ast.nodes.*
+
+class Printer(private val buffer: StringBuilder) : NodeVisitor<Unit> {
   private var indent = 0
 
   private fun append(text: String) {
@@ -65,6 +67,8 @@ class Printer(private val buffer: StringBuilder) : Visitor<Unit> {
         }
         append(" ")
       }
+    } else {
+      append(" ")
     }
     append("in")
     indent++

src/main/kotlin/gay/pizza/pork/ast/Program.kt

@@ -1,8 +0,0 @@
-package gay.pizza.pork.ast
-
-class Program(val expressions: List<Expression>) : Node() {
-  override val type: NodeType = NodeType.Program
-
-  override fun <T> visitChildren(visitor: Visitor<T>): List<T> =
-    visitor.visitAll(expressions)
-}

src/main/kotlin/gay/pizza/pork/ast/SymbolReference.kt

@@ -1,8 +0,0 @@
-package gay.pizza.pork.ast
-
-class SymbolReference(val symbol: Symbol) : Expression() {
-  override val type: NodeType = NodeType.SymbolReference
-
-  override fun <T> visitChildren(visitor: Visitor<T>): List<T> =
-    visitor.visitNodes(symbol)
-}

src/main/kotlin/gay/pizza/pork/ast/nodes/BooleanLiteral.kt

@@ -1,4 +1,6 @@
-package gay.pizza.pork.ast
+package gay.pizza.pork.ast.nodes
+
+import gay.pizza.pork.ast.NodeType
 
 class BooleanLiteral(val value: Boolean) : Expression() {
   override val type: NodeType = NodeType.BooleanLiteral

src/main/kotlin/gay/pizza/pork/ast/nodes/Define.kt

@@ -0,0 +1,11 @@
+package gay.pizza.pork.ast.nodes
+
+import gay.pizza.pork.ast.NodeType
+import gay.pizza.pork.ast.NodeVisitor
+
+class Define(val symbol: Symbol, val value: Expression) : Expression() {
+  override val type: NodeType = NodeType.Define
+
+  override fun <T> visitChildren(visitor: NodeVisitor<T>): List<T> =
+    visitor.visitNodes(symbol, value)
+}

src/main/kotlin/gay/pizza/pork/ast/nodes/Expression.kt

@@ -1,3 +1,3 @@
-package gay.pizza.pork.ast
+package gay.pizza.pork.ast.nodes
 
 abstract class Expression : Node()

src/main/kotlin/gay/pizza/pork/ast/nodes/FunctionCall.kt

@@ -1,8 +1,11 @@
-package gay.pizza.pork.ast
+package gay.pizza.pork.ast.nodes
+
+import gay.pizza.pork.ast.NodeType
+import gay.pizza.pork.ast.NodeVisitor
 
 class FunctionCall(val symbol: Symbol, val arguments: List<Expression>) : Expression() {
   override val type: NodeType = NodeType.FunctionCall
 
-  override fun <T> visitChildren(visitor: Visitor<T>): List<T> =
+  override fun <T> visitChildren(visitor: NodeVisitor<T>): List<T> =
     visitor.visitAll(listOf(symbol), arguments)
 }

src/main/kotlin/gay/pizza/pork/ast/nodes/If.kt

@@ -1,4 +1,6 @@
-package gay.pizza.pork.ast
+package gay.pizza.pork.ast.nodes
+
+import gay.pizza.pork.ast.NodeType
 
 class If(
   val condition: Expression,

src/main/kotlin/gay/pizza/pork/ast/nodes/InfixOperation.kt

@@ -1,8 +1,11 @@
-package gay.pizza.pork.ast
+package gay.pizza.pork.ast.nodes
+
+import gay.pizza.pork.ast.NodeType
+import gay.pizza.pork.ast.NodeVisitor
 
 class InfixOperation(val left: Expression, val op: InfixOperator, val right: Expression) : Expression() {
   override val type: NodeType = NodeType.InfixOperation
 
-  override fun <T> visitChildren(visitor: Visitor<T>): List<T> =
+  override fun <T> visitChildren(visitor: NodeVisitor<T>): List<T> =
     visitor.visitNodes(left, right)
 }

src/main/kotlin/gay/pizza/pork/ast/nodes/InfixOperator.kt

@@ -1,4 +1,4 @@
-package gay.pizza.pork.ast
+package gay.pizza.pork.ast.nodes
 
 enum class InfixOperator(val token: String) {
   Plus("+"),

src/main/kotlin/gay/pizza/pork/ast/nodes/IntLiteral.kt

@@ -1,4 +1,6 @@
-package gay.pizza.pork.ast
+package gay.pizza.pork.ast.nodes
+
+import gay.pizza.pork.ast.NodeType
 
 class IntLiteral(val value: Int) : Expression() {
   override val type: NodeType = NodeType.IntLiteral

src/main/kotlin/gay/pizza/pork/ast/nodes/Lambda.kt

@@ -1,8 +1,11 @@
-package gay.pizza.pork.ast
+package gay.pizza.pork.ast.nodes
+
+import gay.pizza.pork.ast.NodeType
+import gay.pizza.pork.ast.NodeVisitor
 
 class Lambda(val arguments: List<Symbol>, val expressions: List<Expression>) : Expression() {
   override val type: NodeType = NodeType.Lambda
 
-  override fun <T> visitChildren(visitor: Visitor<T>): List<T> =
+  override fun <T> visitChildren(visitor: NodeVisitor<T>): List<T> =
     visitor.visitAll(arguments, expressions)
 }

src/main/kotlin/gay/pizza/pork/ast/nodes/ListLiteral.kt

@@ -0,0 +1,11 @@
+package gay.pizza.pork.ast.nodes
+
+import gay.pizza.pork.ast.NodeType
+import gay.pizza.pork.ast.NodeVisitor
+
+class ListLiteral(val items: List<Expression>) : Expression() {
+  override val type: NodeType = NodeType.ListLiteral
+
+  override fun <T> visitChildren(visitor: NodeVisitor<T>): List<T> =
+    visitor.visitAll(items)
+}

src/main/kotlin/gay/pizza/pork/ast/nodes/Node.kt

@@ -0,0 +1,12 @@
+package gay.pizza.pork.ast.nodes
+
+import gay.pizza.pork.ast.NodeType
+import gay.pizza.pork.ast.Printer
+import gay.pizza.pork.ast.NodeVisitor
+
+abstract class Node {
+  abstract val type: NodeType
+  open fun <T> visitChildren(visitor: NodeVisitor<T>): List<T> = emptyList()
+
+  override fun toString(): String = let { node -> buildString { Printer(this).visit(node) } }
+}

src/main/kotlin/gay/pizza/pork/ast/nodes/Parentheses.kt

@@ -0,0 +1,11 @@
+package gay.pizza.pork.ast.nodes
+
+import gay.pizza.pork.ast.NodeType
+import gay.pizza.pork.ast.NodeVisitor
+
+class Parentheses(val expression: Expression) : Expression() {
+  override val type: NodeType = NodeType.Parentheses
+
+  override fun <T> visitChildren(visitor: NodeVisitor<T>): List<T> =
+    visitor.visitNodes(expression)
+}

src/main/kotlin/gay/pizza/pork/ast/nodes/PrefixOperation.kt

@@ -1,4 +1,6 @@
-package gay.pizza.pork.ast
+package gay.pizza.pork.ast.nodes
+
+import gay.pizza.pork.ast.NodeType
 
 class PrefixOperation(val op: PrefixOperator, val expression: Expression) : Expression() {
   override val type: NodeType = NodeType.PrefixOperation

src/main/kotlin/gay/pizza/pork/ast/nodes/PrefixOperator.kt

@@ -1,4 +1,4 @@
-package gay.pizza.pork.ast
+package gay.pizza.pork.ast.nodes
 
 enum class PrefixOperator(val token: String) {
   Negate("!")

src/main/kotlin/gay/pizza/pork/ast/nodes/Program.kt

@@ -0,0 +1,11 @@
+package gay.pizza.pork.ast.nodes
+
+import gay.pizza.pork.ast.NodeType
+import gay.pizza.pork.ast.NodeVisitor
+
+class Program(val expressions: List<Expression>) : Node() {
+  override val type: NodeType = NodeType.Program
+
+  override fun <T> visitChildren(visitor: NodeVisitor<T>): List<T> =
+    visitor.visitAll(expressions)
+}

src/main/kotlin/gay/pizza/pork/ast/nodes/Symbol.kt

@@ -1,4 +1,6 @@
-package gay.pizza.pork.ast
+package gay.pizza.pork.ast.nodes
+
+import gay.pizza.pork.ast.NodeType
 
 class Symbol(val id: String) : Node() {
   override val type: NodeType = NodeType.Symbol

src/main/kotlin/gay/pizza/pork/ast/nodes/SymbolReference.kt

@@ -0,0 +1,11 @@
+package gay.pizza.pork.ast.nodes
+
+import gay.pizza.pork.ast.NodeType
+import gay.pizza.pork.ast.NodeVisitor
+
+class SymbolReference(val symbol: Symbol) : Expression() {
+  override val type: NodeType = NodeType.SymbolReference
+
+  override fun <T> visitChildren(visitor: NodeVisitor<T>): List<T> =
+    visitor.visitNodes(symbol)
+}

src/main/kotlin/gay/pizza/pork/compiler/KotlinCompiler.kt

@@ -1,8 +1,9 @@
 package gay.pizza.pork.compiler
 
 import gay.pizza.pork.ast.*
+import gay.pizza.pork.ast.nodes.*
 
-class KotlinCompiler : Visitor<String> {
+class KotlinCompiler : NodeVisitor<String> {
   override fun visitDefine(node: Define): String =
     "val ${visit(node.symbol)} = ${visit(node.value)}"
 

src/main/kotlin/gay/pizza/pork/eval/PorkEvaluator.kt

@@ -1,8 +1,9 @@
 package gay.pizza.pork.eval
 
 import gay.pizza.pork.ast.*
+import gay.pizza.pork.ast.nodes.*
 
-class PorkEvaluator(root: Scope) : Visitor<Any> {
+class PorkEvaluator(root: Scope) : NodeVisitor<Any> {
   private var currentScope: Scope = root
 
   override fun visitDefine(node: Define): Any {

src/main/kotlin/gay/pizza/pork/main.kt

@@ -1,6 +1,7 @@
 package gay.pizza.pork
 
-import gay.pizza.pork.ast.Program
+import gay.pizza.pork.ast.Printer
+import gay.pizza.pork.ast.nodes.Program
 import gay.pizza.pork.eval.Arguments
 import gay.pizza.pork.eval.PorkEvaluator
 import gay.pizza.pork.eval.Scope
@@ -39,9 +40,14 @@ fun main(args: Array<String>) {
   eval(program)
 
   val exactCode = stream.tokens.joinToString("") { it.text }
-  println(exactCode)
-  println(code == exactCode)
   validateTokenSoundness(code, stream)
+  if (exactCode != code) {
+    throw RuntimeException("Token reconstruction didn't succeed.")
+  }
+
+  val generated = buildString { Printer(this).visit(program) }
+  parse(tokenize(generated))
+  println(generated)
 }
 
 fun tokenize(input: String): TokenStream =

src/main/kotlin/gay/pizza/pork/parse/PorkParser.kt

@@ -1,6 +1,6 @@
 package gay.pizza.pork.parse
 
-import gay.pizza.pork.ast.*
+import gay.pizza.pork.ast.nodes.*
 
 class PorkParser(source: PeekableSource<Token>) {
   private val whitespaceIncludedSource = source