vm: very basic virtual machine

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

@@ -0,0 +1,42 @@
+package gay.pizza.pork.ast
+
+import gay.pizza.pork.ast.gen.*
+
+abstract class FunctionLevelVisitor<T> : NodeVisitor<T> {
+  override fun visitForInItem(node: ForInItem): T =
+    throw RuntimeException("Visiting ForInItem is not supported.")
+
+  override fun visitSymbol(node: Symbol): T =
+    throw RuntimeException("Visiting Symbol is not supported.")
+
+  override fun visitLetDefinition(node: LetDefinition): T {
+    topLevelUsedError("LetDefinition")
+  }
+
+  override fun visitArgumentSpec(node: ArgumentSpec): T =
+    throw RuntimeException("Visiting ArgumentSpec is not supported.")
+
+  override fun visitFunctionDefinition(node: FunctionDefinition): T {
+    topLevelUsedError("FunctionDefinition")
+  }
+
+  override fun visitImportDeclaration(node: ImportDeclaration): T {
+    topLevelUsedError("ImportDeclaration")
+  }
+
+  override fun visitImportPath(node: ImportPath): T {
+    topLevelUsedError("ImportPath")
+  }
+
+  override fun visitCompilationUnit(node: CompilationUnit): T {
+    topLevelUsedError("CompilationUnit")
+  }
+
+  override fun visitNativeFunctionDescriptor(node: NativeFunctionDescriptor): T {
+    topLevelUsedError("NativeFunctionDescriptor")
+  }
+
+  private fun topLevelUsedError(name: String): Nothing {
+    throw RuntimeException("$name cannot be visited in a FunctionVisitor.")
+  }
+}

bytecode/build.gradle.kts

@@ -0,0 +1,7 @@
+plugins {
+  id("gay.pizza.pork.module")
+}
+
+dependencies {
+  implementation(project(":common"))
+}

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

@@ -0,0 +1,10 @@
+package gay.pizza.pork.bytecode
+
+import kotlinx.serialization.Serializable
+
+@Serializable
+data class CompiledWorld(
+  val constantPool: ConstantPool,
+  val symbolTable: SymbolTable,
+  val code: List<Op>
+)

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

@@ -0,0 +1,3 @@
+package gay.pizza.pork.bytecode
+
+class Constant(val id: UInt, val value: ByteArray)

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

@@ -0,0 +1,6 @@
+package gay.pizza.pork.bytecode
+
+import kotlinx.serialization.Serializable
+
+@Serializable
+data class ConstantPool(val constants: List<ByteArray>)

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

@@ -0,0 +1,18 @@
+package gay.pizza.pork.bytecode
+
+class MutableConstantPool {
+  private val pool = mutableListOf<Constant>()
+
+  fun assign(content: ByteArray): UInt {
+    for (constant in pool) {
+      if (constant.value.contentEquals(content)) {
+        return constant.id
+      }
+    }
+    val id = pool.size.toUInt()
+    pool.add(Constant(id, content))
+    return id
+  }
+
+  fun all(): List<Constant> = pool
+}

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

@@ -0,0 +1,3 @@
+package gay.pizza.pork.bytecode
+
+class MutableRel(var rel: UInt)

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

@@ -0,0 +1,6 @@
+package gay.pizza.pork.bytecode
+
+import kotlinx.serialization.Serializable
+
+@Serializable
+data class Op(val code: Opcode, val args: List<UInt>)

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

@@ -0,0 +1,43 @@
+package gay.pizza.pork.bytecode
+
+enum class Opcode(val id: UByte) {
+  Constant(1u),
+  None(2u),
+  False(3u),
+  True(4u),
+  Pop(5u),
+  Jump(6u),
+  JumpIf(7u),
+  Not(8u),
+  UnaryPlus(9u),
+  UnaryMinus(10u),
+  BinaryNot(11u),
+  And(20u),
+  Native(24u),
+  Return(10u),
+  StoreLocal(16u),
+  LoadLocal(17u),
+  Add(18u),
+  Subtract(19u),
+  Multiply(20u),
+  Divide(21u),
+  CompareEqual(22u),
+  CompareLesser(23u),
+  CompareGreater(24u),
+  CompareLesserEqual(25u),
+  CompareGreaterEqual(26u),
+  Or(27u),
+  BinaryAnd(28u),
+  BinaryOr(29u),
+  BinaryXor(30u),
+  List(31u),
+  Integer(32u),
+  Double(33u),
+  Call(34u),
+  EuclideanModulo(35u),
+  Remainder(36u),
+  Index(37u),
+  ScopeIn(38u),
+  ScopeOut(39u),
+  End(255u),
+}

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

@@ -0,0 +1,3 @@
+package gay.pizza.pork.bytecode
+
+class Ops(val ops: List<Op>)

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

@@ -0,0 +1,10 @@
+package gay.pizza.pork.bytecode
+
+import kotlinx.serialization.Serializable
+
+@Serializable
+data class SymbolInfo(
+  val id: String,
+  val offset: UInt,
+  val size: UInt
+)

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

@@ -0,0 +1,8 @@
+package gay.pizza.pork.bytecode
+
+import kotlinx.serialization.Serializable
+
+@Serializable
+data class SymbolTable(
+  val symbols: List<SymbolInfo>
+)

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

@@ -0,0 +1,40 @@
+package gay.pizza.pork.common
+
+object ByteRepresentation {
+  fun encode(value: Int): ByteArray {
+    val buffer = ByteArray(4)
+    encode(value, buffer, 0)
+    return buffer
+  }
+
+  fun encode(value: Long): ByteArray {
+    val buffer = ByteArray(8)
+    encode(value, buffer, 0)
+    return buffer
+  }
+
+  fun encode(value: Double): ByteArray =
+    encode(value.toRawBits())
+
+  fun encode(value: Int, buffer: ByteArray, offset: Int) {
+    buffer[offset + 0] = (value shr 0).toByte()
+    buffer[offset + 1] = (value shr 8).toByte()
+    buffer[offset + 2] = (value shr 16).toByte()
+    buffer[offset + 3] = (value shr 24).toByte()
+  }
+
+  fun encode(value: Long, buffer: ByteArray, offset: Int) {
+    buffer[offset + 0] = (value shr 0).toByte()
+    buffer[offset + 1] = (value shr 8).toByte()
+    buffer[offset + 2] = (value shr 16).toByte()
+    buffer[offset + 3] = (value shr 24).toByte()
+    buffer[offset + 4] = (value shr 32).toByte()
+    buffer[offset + 5] = (value shr 40).toByte()
+    buffer[offset + 6] = (value shr 48).toByte()
+    buffer[offset + 7] = (value shr 56).toByte()
+  }
+
+  fun encode(value: Double, buffer: ByteArray, offset: Int) {
+    encode(value.toRawBits(), buffer, offset)
+  }
+}

compiler/build.gradle.kts

@@ -0,0 +1,11 @@
+plugins {
+  id("gay.pizza.pork.module")
+}
+
+dependencies {
+  api(project(":ast"))
+  api(project(":bytecode"))
+  api(project(":parser"))
+  api(project(":frontend"))
+  implementation(project(":common"))
+}

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

@@ -0,0 +1,16 @@
+package gay.pizza.pork.compiler
+
+import gay.pizza.pork.ast.gen.Symbol
+import gay.pizza.pork.frontend.Slab
+
+class CompilableSlab(val compiler: Compiler, val slab: Slab) {
+  val compilableSymbols: List<CompilableSymbol> by lazy {
+    slab.scope.internalSymbols.map { symbol ->
+      CompilableSymbol(this, symbol)
+    }
+  }
+
+  fun compilableSymbolOf(symbol: Symbol): CompilableSymbol? = compilableSymbols.firstOrNull {
+    it.scopeSymbol.symbol == symbol
+  }
+}

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

@@ -0,0 +1,34 @@
+package gay.pizza.pork.compiler
+
+import gay.pizza.pork.ast.gen.FunctionDefinition
+import gay.pizza.pork.ast.gen.LetDefinition
+import gay.pizza.pork.ast.gen.visit
+import gay.pizza.pork.frontend.scope.ScopeSymbol
+
+class CompilableSymbol(val compilableSlab: CompilableSlab, val scopeSymbol: ScopeSymbol) {
+  val compiledStubOps: List<StubOp> by lazy { compile() }
+
+  val usedSymbols: List<ScopeSymbol>
+    get() = scopeSymbol.scope.usedSymbols
+
+  private fun compile(): List<StubOp> {
+    val emitter = StubOpEmitter(compilableSlab.compiler, this)
+    emitter.enter()
+    val what = if (scopeSymbol.definition is FunctionDefinition) {
+      val functionDefinition = scopeSymbol.definition as FunctionDefinition
+      emitter.allocateOuterScope(functionDefinition)
+      functionDefinition.block ?: functionDefinition.nativeFunctionDescriptor!!
+    } else {
+      val letDefinition = scopeSymbol.definition as LetDefinition
+      letDefinition.value
+    }
+    emitter.visit(what)
+    emitter.exit()
+    return emitter.ops()
+  }
+
+  val id: String
+    get() = "${compilableSlab.slab.location.commonFriendlyName} ${scopeSymbol.symbol.id}"
+
+  override fun toString(): String = "${compilableSlab.slab.location.commonFriendlyName} ${scopeSymbol.symbol.id}"
+}

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

@@ -0,0 +1,38 @@
+package gay.pizza.pork.compiler
+
+import gay.pizza.pork.bytecode.*
+
+class CompiledWorldLayout(val compiler: Compiler) : StubResolutionContext {
+  private val allStubOps = mutableListOf<StubOp>()
+  private val symbolTable = mutableMapOf<CompilableSymbol, SymbolInfo>()
+
+  fun add(symbol: CompilableSymbol) {
+    val start = allStubOps.size
+    val stubOps = symbol.compiledStubOps
+    symbolTable[symbol] = SymbolInfo(symbol.id, start.toUInt(), stubOps.size.toUInt())
+    allStubOps.addAll(stubOps)
+  }
+
+  private fun patch(): List<Op> {
+    val ops = mutableListOf<Op>()
+    for (stub in allStubOps) {
+      val actualArguments = stub.op.args.toMutableList()
+      stub.patch(this, actualArguments)
+      ops.add(Op(stub.op.code, actualArguments))
+    }
+    return ops
+  }
+
+  override fun resolveJumpTarget(symbol: CompilableSymbol): UInt {
+    return symbolTable[symbol]?.offset ?:
+      throw RuntimeException("Unable to resolve jump target: ${symbol.scopeSymbol.symbol.id}")
+  }
+
+  fun layoutCompiledWorld(): CompiledWorld {
+    val constantPool = mutableListOf<ByteArray>()
+    for (item in compiler.constantPool.all()) {
+      constantPool.add(item.value)
+    }
+    return CompiledWorld(ConstantPool(constantPool), SymbolTable(symbolTable.values.toList()), patch())
+  }
+}

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

@@ -0,0 +1,47 @@
+package gay.pizza.pork.compiler
+
+import gay.pizza.pork.bytecode.CompiledWorld
+import gay.pizza.pork.bytecode.MutableConstantPool
+import gay.pizza.pork.frontend.Slab
+import gay.pizza.pork.frontend.scope.ScopeSymbol
+
+class Compiler {
+  val constantPool: MutableConstantPool = MutableConstantPool()
+  val compilableSlabs: ComputableState<Slab, CompilableSlab> = ComputableState { slab ->
+    CompilableSlab(this, slab)
+  }
+
+  fun resolveOrNull(scopeSymbol: ScopeSymbol): CompilableSymbol? {
+    val compiledSlab = compilableSlabs.of(scopeSymbol.slabScope.slab)
+    return compiledSlab.compilableSymbolOf(scopeSymbol.symbol)
+  }
+
+  fun resolve(scopeSymbol: ScopeSymbol): CompilableSymbol = resolveOrNull(scopeSymbol) ?:
+    throw RuntimeException(
+      "Unable to resolve scope symbol: " +
+      "${scopeSymbol.slabScope.slab.location.commonFriendlyName} ${scopeSymbol.symbol.id}")
+
+  fun contributeCompiledSymbols(
+    into: MutableSet<CompilableSymbol>,
+    symbol: ScopeSymbol,
+    resolved: CompilableSymbol = resolve(symbol)
+  ) {
+    if (!into.add(resolved)) {
+      return
+    }
+
+    for (used in resolved.usedSymbols) {
+      contributeCompiledSymbols(into, used)
+    }
+  }
+
+  fun compile(entryPointSymbol: CompilableSymbol): CompiledWorld {
+    val usedSymbolSet = mutableSetOf<CompilableSymbol>()
+    contributeCompiledSymbols(usedSymbolSet, entryPointSymbol.scopeSymbol, entryPointSymbol)
+    val layout = CompiledWorldLayout(this)
+    for (used in usedSymbolSet) {
+      layout.add(used)
+    }
+    return layout.layoutCompiledWorld()
+  }
+}

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

@@ -0,0 +1,7 @@
+package gay.pizza.pork.compiler
+
+class ComputableState<X, T>(val computation: (X) -> T) {
+  private val state = StoredState<X, T>()
+
+  fun of(key: X): T = state.computeIfAbsent(key, computation)
+}

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

@@ -0,0 +1,11 @@
+package gay.pizza.pork.compiler
+
+import gay.pizza.pork.bytecode.MutableRel
+
+class LoopState(
+  val startOfLoop: UInt,
+  val exitJumpTarget: MutableRel,
+  val body: MutableRel,
+  val scopeDepth: Int,
+  val enclosing: LoopState? = null
+)

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

@@ -0,0 +1,12 @@
+package gay.pizza.pork.compiler
+
+import gay.pizza.pork.bytecode.MutableRel
+import gay.pizza.pork.bytecode.Op
+
+class PatchRelOp(op: Op, val index: Int, val symbol: CompilableSymbol, val rel: MutableRel) : StubOp(op) {
+  override fun patch(context: StubResolutionContext, arguments: MutableList<UInt>) {
+    arguments[index] = context.resolveJumpTarget(symbol) + rel.rel
+  }
+
+  override fun toString(): String = "PatchRelOp(${op}, ${index}, ${symbol}, ${rel})"
+}

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

@@ -0,0 +1,13 @@
+package gay.pizza.pork.compiler
+
+import gay.pizza.pork.bytecode.Op
+
+class PatchSymOp(op: Op, val patches: Map<Int, CompilableSymbol>) : StubOp(op) {
+  override fun patch(context: StubResolutionContext, arguments: MutableList<UInt>) {
+    for ((index, symbol) in patches) {
+      arguments[index] = context.resolveJumpTarget(symbol)
+    }
+  }
+
+  override fun toString(): String = "PatchSymOp(${op}, ${patches})"
+}

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

@@ -0,0 +1,7 @@
+package gay.pizza.pork.compiler
+
+import gay.pizza.pork.bytecode.Op
+
+class StaticOp(op: Op) : StubOp(op) {
+  override fun toString(): String = "StaticOp(${op})"
+}

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

@@ -0,0 +1,11 @@
+package gay.pizza.pork.compiler
+
+class StoredState<X, T> {
+  private val state = mutableMapOf<X, T>()
+
+  fun computeIfAbsent(key: X, computation: (X) -> T): T = state.computeIfAbsent(key, computation)
+  fun of(key: X): T? = state[key]
+  fun put(key: X, value: T) {
+    state[key] = value
+  }
+}

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

@@ -0,0 +1,7 @@
+package gay.pizza.pork.compiler
+
+import gay.pizza.pork.bytecode.Op
+
+abstract class StubOp(val op: Op) {
+  open fun patch(context: StubResolutionContext, arguments: MutableList<UInt>) {}
+}

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

@@ -0,0 +1,336 @@
+package gay.pizza.pork.compiler
+
+import gay.pizza.pork.ast.FunctionLevelVisitor
+import gay.pizza.pork.ast.gen.*
+import gay.pizza.pork.bytecode.MutableRel
+import gay.pizza.pork.bytecode.Op
+import gay.pizza.pork.bytecode.Opcode
+
+class StubOpEmitter(val compiler: Compiler, val symbol: CompilableSymbol) : FunctionLevelVisitor<Unit>() {
+  private val ops = mutableListOf<StubOp>()
+
+  private var loopState: LoopState? = null
+  private val localVariables = mutableListOf<MutableList<StubVar>>()
+  private var localVarIndex = 0u
+
+  private val requiredLoopState: LoopState
+    get() {
+      if (loopState != null) {
+        return loopState!!
+      }
+      throw RuntimeException("loopState expected but was not found.")
+    }
+
+  private fun allocateLocalVariable(symbol: Symbol): StubVar {
+    val scope = localVariables.last()
+    val variable = StubVar(localVarIndex++, symbol)
+    scope.add(variable)
+    return variable
+  }
+
+  private fun resolveSymbol(symbol: Symbol): CallOrStubVar {
+    for (scope in localVariables.reversed()) {
+      val found = scope.firstOrNull { it.symbol == symbol }
+      if (found != null) {
+        return CallOrStubVar(stubVar = found)
+      }
+    }
+    val found = this.symbol.compilableSlab.compilableSymbolOf(symbol)
+    if (found != null) {
+      return CallOrStubVar(call = found)
+    }
+    throw RuntimeException("Unable to resolve symbol: ${symbol.id}")
+  }
+
+  private fun pushScope() {
+    emit(Opcode.ScopeIn)
+    localVariables.add(mutableListOf())
+  }
+
+  private fun popScope() {
+    emit(Opcode.ScopeOut)
+    localVariables.removeLast()
+  }
+
+  fun enter() {
+    pushScope()
+  }
+
+  fun allocateOuterScope(definition: FunctionDefinition) {
+    val allNormalArguments = definition.arguments.takeWhile { !it.multiple }
+    val varArgument = definition.arguments.firstOrNull { it.multiple }
+
+    for (arg in allNormalArguments.reversed()) {
+      val functionLocal = allocateLocalVariable(arg.symbol)
+      emit(Opcode.StoreLocal, listOf(functionLocal.index))
+    }
+
+    if (varArgument != null) {
+      val functionLocal = allocateLocalVariable(varArgument.symbol)
+      emit(Opcode.StoreLocal, listOf(functionLocal.index))
+    }
+  }
+
+  fun exit() {
+    popScope()
+    emit(Opcode.Return)
+  }
+
+  override fun visitBlock(node: Block) {
+    pushScope()
+    node.visitChildren(this)
+    popScope()
+  }
+
+  override fun visitBooleanLiteral(node: BooleanLiteral) {
+    emit(if (node.value) Opcode.True else Opcode.False)
+  }
+
+  override fun visitBreak(node: Break) {
+    patch(Opcode.Jump, listOf(0u), 0, symbol, requiredLoopState.exitJumpTarget)
+  }
+
+  override fun visitContinue(node: Continue) {
+    patch(Opcode.Jump, listOf(0u), 0, symbol, requiredLoopState.startOfLoop)
+  }
+
+  override fun visitDoubleLiteral(node: DoubleLiteral) {
+    emit(Opcode.Integer, listOf(node.value.toUInt()))
+  }
+
+  override fun visitForIn(node: ForIn) {
+    TODO("ForIn is currently unsupported")
+  }
+
+  override fun visitFunctionCall(node: FunctionCall) {
+    val targetScopeSymbol = symbol.scopeSymbol.scope.resolve(node.symbol) ?:
+      throw RuntimeException("Unable to resolve symbol: ${node.symbol.id}")
+    val targetSymbol = compiler.resolve(targetScopeSymbol)
+    val functionDefinition = targetSymbol.scopeSymbol.definition as FunctionDefinition
+    val retRel = MutableRel(0u)
+    patch(Opcode.Integer, listOf(0u), 0, symbol, retRel)
+
+    val normalArguments = mutableListOf<Expression>()
+    var variableArguments: List<Expression>? = null
+    for ((index, item) in functionDefinition.arguments.zip(node.arguments).withIndex()) {
+      val (spec, value) = item
+      if (spec.multiple) {
+        val remaining = node.arguments.drop(index)
+        variableArguments = remaining
+        break
+      } else {
+        normalArguments.add(value)
+      }
+    }
+
+    if (variableArguments != null) {
+      for (item in variableArguments.reversed()) {
+        item.visit(this)
+      }
+      emit(Opcode.List, listOf(variableArguments.size.toUInt()))
+    }
+
+    for (item in normalArguments.reversed()) {
+      visit(item)
+    }
+
+    retRel.rel = (ops.size + 1).toUInt()
+    patch(Opcode.Call, listOf(0u), mapOf(0 to targetSymbol))
+  }
+
+  override fun visitIf(node: If) {
+    val thenRel = MutableRel(0u)
+    val endRel = MutableRel(0u)
+    node.condition.visit(this)
+    patch(Opcode.JumpIf, listOf(0u), 0, symbol, thenRel)
+    node.elseBlock?.visit(this)
+    patch(Opcode.Jump, listOf(0u), 0, symbol, endRel)
+    thenRel.rel = ops.size.toUInt()
+    node.thenBlock.visit(this)
+    endRel.rel = ops.size.toUInt()
+  }
+
+  override fun visitIndexedBy(node: IndexedBy) {
+    node.expression.visit(this)
+    node.index.visit(this)
+    emit(Opcode.Index)
+  }
+
+  override fun visitInfixOperation(node: InfixOperation) {
+    node.left.visit(this)
+    node.right.visit(this)
+    when (node.op) {
+      InfixOperator.Plus -> emit(Opcode.Add)
+      InfixOperator.Minus -> emit(Opcode.Subtract)
+      InfixOperator.Multiply -> emit(Opcode.Multiply)
+      InfixOperator.Divide -> emit(Opcode.Divide)
+      InfixOperator.Equals -> emit(Opcode.CompareEqual)
+      InfixOperator.NotEquals -> {
+        emit(Opcode.CompareEqual)
+        emit(Opcode.Not)
+      }
+      InfixOperator.EuclideanModulo -> emit(Opcode.EuclideanModulo)
+      InfixOperator.Remainder -> emit(Opcode.Remainder)
+      InfixOperator.Lesser -> emit(Opcode.CompareLesser)
+      InfixOperator.Greater -> emit(Opcode.CompareGreater)
+      InfixOperator.GreaterEqual -> emit(Opcode.CompareGreaterEqual)
+      InfixOperator.LesserEqual -> emit(Opcode.CompareLesserEqual)
+      InfixOperator.BooleanAnd -> emit(Opcode.And)
+      InfixOperator.BooleanOr -> emit(Opcode.Or)
+      InfixOperator.BinaryAnd -> emit(Opcode.BinaryAnd)
+      InfixOperator.BinaryOr -> emit(Opcode.BinaryOr)
+      InfixOperator.BinaryExclusiveOr -> emit(Opcode.BinaryXor)
+    }
+  }
+
+  override fun visitIntegerLiteral(node: IntegerLiteral) {
+    emit(Opcode.Integer, listOf(node.value.toUInt()))
+  }
+
+  override fun visitLetAssignment(node: LetAssignment) {
+    val variable = allocateLocalVariable(node.symbol)
+    node.value.visit(this)
+    emit(Opcode.StoreLocal, listOf(variable.index))
+  }
+
+  override fun visitListLiteral(node: ListLiteral) {
+    val count = node.items.size
+    for (item in node.items) {
+      item.visit(this)
+    }
+    emit(Opcode.List, listOf(count.toUInt()))
+  }
+
+  override fun visitLongLiteral(node: LongLiteral) {
+    emit(Opcode.Integer, listOf(node.value.toUInt()))
+  }
+
+  override fun visitNoneLiteral(node: NoneLiteral) {
+    emit(Opcode.None)
+  }
+
+  override fun visitParentheses(node: Parentheses) {
+    node.expression.visit(this)
+  }
+
+  override fun visitPrefixOperation(node: PrefixOperation) {
+    node.expression.visit(this)
+    when (node.op) {
+      PrefixOperator.BooleanNot -> emit(Opcode.Not)
+      PrefixOperator.UnaryPlus -> emit(Opcode.UnaryPlus)
+      PrefixOperator.UnaryMinus -> emit(Opcode.UnaryMinus)
+      PrefixOperator.BinaryNot -> emit(Opcode.BinaryNot)
+    }
+  }
+
+  override fun visitSetAssignment(node: SetAssignment) {
+    val stubVarOrCall = resolveSymbol(node.symbol)
+    if (stubVarOrCall.stubVar == null) {
+      throw RuntimeException("Invalid set assignment.")
+    }
+    node.value.visit(this)
+    emit(Opcode.StoreLocal, listOf(stubVarOrCall.stubVar.index))
+  }
+
+  override fun visitStringLiteral(node: StringLiteral) {
+    val bytes = node.text.toByteArray()
+    val constant = compiler.constantPool.assign(bytes)
+    emit(Opcode.Constant, listOf(constant))
+  }
+
+  override fun visitSuffixOperation(node: SuffixOperation) {
+    val stubVarOrCall = resolveSymbol(node.reference.symbol)
+    if (stubVarOrCall.stubVar == null) {
+      throw RuntimeException("Invalid suffix operation.")
+    }
+    load(stubVarOrCall)
+    when (node.op) {
+      SuffixOperator.Increment -> {
+        emit(Opcode.Integer, listOf(1u))
+        emit(Opcode.Add, emptyList())
+        emit(Opcode.StoreLocal, listOf(stubVarOrCall.stubVar.index))
+      }
+      SuffixOperator.Decrement -> {
+        emit(Opcode.Integer, listOf(1u))
+        emit(Opcode.Subtract, emptyList())
+        emit(Opcode.StoreLocal, listOf(stubVarOrCall.stubVar.index))
+      }
+    }
+  }
+
+  override fun visitSymbolReference(node: SymbolReference) {
+    val variable = resolveSymbol(node.symbol)
+    load(variable)
+  }
+
+  override fun visitVarAssignment(node: VarAssignment) {
+    val variable = allocateLocalVariable(node.symbol)
+    node.value.visit(this)
+    emit(Opcode.StoreLocal, listOf(variable.index))
+  }
+
+  override fun visitWhile(node: While) {
+    val startOfBody = MutableRel(0u)
+    val endOfLoop = MutableRel(0u)
+    val currentLoopState = LoopState(
+      startOfLoop = ops.size.toUInt(),
+      exitJumpTarget = endOfLoop,
+      body = startOfBody,
+      scopeDepth = (loopState?.scopeDepth ?: 0) + 1,
+      enclosing = loopState
+    )
+    loopState = currentLoopState
+    node.condition.visit(this)
+    patch(Opcode.JumpIf, listOf(0u), 0, symbol, startOfBody)
+    patch(Opcode.Jump, listOf(0u), 0, symbol, endOfLoop)
+    startOfBody.rel = ops.size.toUInt()
+    node.block.visit(this)
+    patch(Opcode.Jump, listOf(0u), 0, symbol, currentLoopState.startOfLoop)
+    endOfLoop.rel = ops.size.toUInt()
+  }
+
+  override fun visitNativeFunctionDescriptor(node: NativeFunctionDescriptor) {
+    for (def in node.definitions) {
+      val defConstant = compiler.constantPool.assign(def.text.toByteArray())
+      emit(Opcode.Constant, listOf(defConstant))
+    }
+    val formConstant = compiler.constantPool.assign(node.form.id.toByteArray())
+    emit(Opcode.Native, listOf(formConstant, node.definitions.size.toUInt()))
+  }
+
+  private fun emit(code: Opcode) {
+    emit(code, emptyList())
+  }
+
+  private fun emit(code: Opcode, arguments: List<UInt>) {
+    ops.add(StaticOp(Op(code, arguments)))
+  }
+
+  private fun patch(code: Opcode, arguments: List<UInt>, index: Int, symbol: CompilableSymbol, rel: MutableRel) {
+    ops.add(PatchRelOp(Op(code, arguments), index, symbol, rel))
+  }
+
+  private fun patch(code: Opcode, arguments: List<UInt>, index: Int, symbol: CompilableSymbol, rel: UInt) {
+    ops.add(PatchRelOp(Op(code, arguments), index, symbol, MutableRel(rel)))
+  }
+
+  private fun patch(code: Opcode, arguments: List<UInt>, patches: Map<Int, CompilableSymbol>) {
+    ops.add(PatchSymOp(Op(code, arguments), patches))
+  }
+
+  fun ops(): List<StubOp> = ops
+
+  private fun load(callOrStubVar: CallOrStubVar) {
+    if (callOrStubVar.stubVar != null) {
+      emit(Opcode.LoadLocal, listOf(callOrStubVar.stubVar.index))
+    } else {
+      emit(Opcode.Integer, listOf(ops.size.toUInt() + 2u))
+      patch(Opcode.Call, listOf(0u), mapOf(0 to callOrStubVar.call!!))
+    }
+  }
+
+  private class CallOrStubVar(
+    val call: CompilableSymbol? = null,
+    val stubVar: StubVar? = null
+  )
+}

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

@@ -0,0 +1,5 @@
+package gay.pizza.pork.compiler
+
+interface StubResolutionContext {
+  fun resolveJumpTarget(symbol: CompilableSymbol): UInt
+}

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

@@ -0,0 +1,8 @@
+package gay.pizza.pork.compiler
+
+import gay.pizza.pork.ast.gen.Symbol
+
+class StubVar(
+  val index: UInt,
+  val symbol: Symbol
+)

evaluator/build.gradle.kts

@@ -4,6 +4,7 @@ plugins {
 
 dependencies {
   api(project(":ast"))
+  api(project(":execution"))
   api(project(":frontend"))
 
   implementation(project(":common"))

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

@@ -1,78 +0,0 @@
-package gay.pizza.pork.evaluator
-
-import gay.pizza.pork.ast.gen.*
-import gay.pizza.pork.frontend.ImportLocator
-
-class CompilationUnitContext(
-  val compilationUnit: CompilationUnit,
-  val evaluator: Evaluator,
-  rootScope: Scope,
-  val name: String = "unknown"
-) {
-  val internalScope = rootScope.fork("internal $name")
-  val externalScope = rootScope.fork("external $name")
-
-  private var initialized = false
-
-  fun initIfNeeded() {
-    if (initialized) {
-      return
-    }
-    initialized = true
-    processAllImports()
-    processAllDefinitions()
-  }
-
-  private fun processAllDefinitions() {
-    for (definition in compilationUnit.definitions) {
-      processDefinition(definition)
-    }
-  }
-
-  private fun processDefinition(definition: Definition) {
-    val internalValue = definitionValue(definition)
-    internalScope.define(definition.symbol.id, internalValue)
-    if (definition.modifiers.export) {
-      externalScope.define(definition.symbol.id, internalValue)
-    }
-  }
-
-  private fun definitionValue(definition: Definition): Any = when (definition) {
-    is FunctionDefinition -> FunctionContext(this, definition)
-    is LetDefinition -> {
-      EvaluationVisitor(internalScope.fork("let ${definition.symbol.id}"), CallStack())
-        .visit(definition.value)
-    }
-  }
-
-  private fun processAllImports() {
-    processPreludeImport()
-    val imports = compilationUnit.declarations.filterIsInstance<ImportDeclaration>()
-    for (import in imports) {
-      processImport(import)
-    }
-  }
-
-  private fun processImport(import: ImportDeclaration) {
-    val importPath = import.path.components.joinToString("/") { it.id } + ".pork"
-    val importLocator = ImportLocator(import.form.id, importPath)
-    val evaluationContext = evaluator.context(importLocator)
-    internalScope.inherit(evaluationContext.externalScope)
-  }
-
-  private fun processPreludeImport() {
-    processImport(preludeImport)
-  }
-
-  companion object {
-    private val preludeImport = ImportDeclaration(
-      Symbol("std"),
-      ImportPath(
-        listOf(
-          Symbol("lang"),
-          Symbol("prelude")
-        )
-      )
-    )
-  }
-}

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

@@ -1,10 +1,11 @@
 package gay.pizza.pork.evaluator
 
+import gay.pizza.pork.ast.FunctionLevelVisitor
 import gay.pizza.pork.ast.gen.*
 import kotlin.math.abs
 
 @Suppress("JavaIoSerializableObjectMustHaveReadResolve")
-class EvaluationVisitor(root: Scope, val stack: CallStack) : NodeVisitor<Any> {
+class EvaluationVisitor(root: Scope, val stack: CallStack) : FunctionLevelVisitor<Any>() {
   private var currentScope: Scope = root
 
   override fun visitIntegerLiteral(node: IntegerLiteral): Any = node.value
@@ -66,10 +67,6 @@ class EvaluationVisitor(root: Scope, val stack: CallStack) : NodeVisitor<Any> {
     return value
   }
 
-  override fun visitLetDefinition(node: LetDefinition): Any {
-    topLevelUsedError("LetDefinition", "CompilationUnitContext")
-  }
-
   override fun visitSymbolReference(node: SymbolReference): Any =
     currentScope.value(node.symbol.id)
 
@@ -383,18 +380,6 @@ class EvaluationVisitor(root: Scope, val stack: CallStack) : NodeVisitor<Any> {
     }
   }
 
-  override fun visitFunctionDefinition(node: FunctionDefinition): Any {
-    topLevelUsedError("FunctionDefinition", "FunctionContext")
-  }
-
-  override fun visitImportDeclaration(node: ImportDeclaration): Any {
-    topLevelUsedError("ImportDeclaration", "CompilationUnitContext")
-  }
-
-  override fun visitImportPath(node: ImportPath): Any {
-    topLevelUsedError("ImportPath", "CompilationUnitContext")
-  }
-
   override fun visitIndexedBy(node: IndexedBy): Any {
     val value = node.expression.visit(this)
     val index = node.index.visit(this)
@@ -410,14 +395,6 @@ class EvaluationVisitor(root: Scope, val stack: CallStack) : NodeVisitor<Any> {
     throw RuntimeException("Failed to index '${value}' by '${index}': Unsupported types used.")
   }
 
-  override fun visitCompilationUnit(node: CompilationUnit): Any {
-    topLevelUsedError("CompilationUnit", "CompilationUnitContext")
-  }
-
-  override fun visitNativeFunctionDescriptor(node: NativeFunctionDescriptor): Any {
-    topLevelUsedError("NativeFunctionDescriptor", "FunctionContext")
-  }
-
   override fun visitNoneLiteral(node: NoneLiteral): Any = None
 
   override fun visitContinue(node: Continue): Any = ContinueMarker
@@ -445,13 +422,6 @@ class EvaluationVisitor(root: Scope, val stack: CallStack) : NodeVisitor<Any> {
     throw RuntimeException("Can't perform $operation between floating point types")
   }
 
-  private fun topLevelUsedError(name: String, alternative: String): Nothing {
-    throw RuntimeException(
-      "$name cannot be visited in an EvaluationVisitor. " +
-        "Utilize an $alternative instead."
-    )
-  }
-
   private object BreakMarker : RuntimeException("Break Marker")
   private object ContinueMarker: RuntimeException("Continue Marker")
 }

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

@@ -1,25 +1,33 @@
 package gay.pizza.pork.evaluator
 
+import gay.pizza.pork.ast.gen.Symbol
+import gay.pizza.pork.execution.ExecutionContext
+import gay.pizza.pork.execution.ExecutionContextProvider
 import gay.pizza.pork.frontend.ImportLocator
+import gay.pizza.pork.frontend.Slab
 import gay.pizza.pork.frontend.World
 
-class Evaluator(val world: World, val scope: Scope) {
-  private val contexts = mutableMapOf<String, CompilationUnitContext>()
+class Evaluator(val world: World) : ExecutionContextProvider {
+  private val scope = Scope.root()
+  private val contexts = mutableMapOf<Slab, SlabContext>()
   private val nativeProviders = mutableMapOf<String, NativeProvider>()
 
-  fun evaluate(locator: ImportLocator): Scope =
-    context(locator).externalScope
-
-  fun context(locator: ImportLocator): CompilationUnitContext {
-    val unit = world.load(locator)
-    val identity = world.stableIdentity(locator)
-    val context = contexts.computeIfAbsent(identity) {
-      CompilationUnitContext(unit, this, scope, name = "${locator.form} ${locator.path}")
-    }
-    context.initIfNeeded()
-    return context
+  fun evaluate(locator: ImportLocator): Scope {
+    val slabContext = context(locator)
+    slabContext.finalizeScope()
+    return slabContext.externalScope
   }
 
+  fun context(slab: Slab): SlabContext {
+    val slabContext = contexts.computeIfAbsent(slab) {
+      SlabContext(slab, this, scope)
+    }
+    slabContext.ensureImportedContextsExist()
+    return slabContext
+  }
+
+  fun context(locator: ImportLocator): SlabContext = context(world.load(locator))
+
   fun nativeFunctionProvider(form: String): NativeProvider {
     return nativeProviders[form] ?:
       throw RuntimeException("Unknown native function form: $form")
@@ -28,4 +36,10 @@ class Evaluator(val world: World, val scope: Scope) {
   fun addNativeProvider(form: String, nativeProvider: NativeProvider) {
     nativeProviders[form] = nativeProvider
   }
+
+  override fun prepare(importLocator: ImportLocator, entryPointSymbol: Symbol): ExecutionContext {
+    val slab = context(importLocator)
+    slab.finalizeScope()
+    return EvaluatorExecutionContext(this, slab, entryPointSymbol)
+  }
 }

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

@@ -0,0 +1,18 @@
+package gay.pizza.pork.evaluator
+
+import gay.pizza.pork.ast.gen.Symbol
+import gay.pizza.pork.execution.ExecutionContext
+
+class EvaluatorExecutionContext(val evaluator: Evaluator, val slab: SlabContext, val entryPointSymbol: Symbol) : ExecutionContext {
+  private val function: CallableFunction by lazy {
+    val value = slab.externalScope.value(entryPointSymbol.id)
+    if (value !is CallableFunction) {
+      throw RuntimeException("Symbol '${entryPointSymbol.id}' resolves to a non-function.")
+    }
+    value
+  }
+
+  override fun execute() {
+    function.call(emptyList(), CallStack())
+  }
+}

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

@@ -2,16 +2,16 @@ package gay.pizza.pork.evaluator
 
 import gay.pizza.pork.ast.gen.FunctionDefinition
 
-class FunctionContext(val compilationUnitContext: CompilationUnitContext, val node: FunctionDefinition) : CallableFunction {
-  val name: String = "${compilationUnitContext.name} ${node.symbol.id}"
+class FunctionContext(val slabContext: SlabContext, val node: FunctionDefinition) : CallableFunction {
+  val name: String by lazy { "${slabContext.slab.location.commonFriendlyName} ${node.symbol.id}" }
 
   private fun resolveMaybeNative(): CallableFunction? = if (node.nativeFunctionDescriptor == null) {
     null
   } else {
     val native = node.nativeFunctionDescriptor!!
     val nativeFunctionProvider =
-      compilationUnitContext.evaluator.nativeFunctionProvider(native.form.id)
-    nativeFunctionProvider.provideNativeFunction(native.definitions.map { it.text }, node.arguments, compilationUnitContext)
+      slabContext.evaluator.nativeFunctionProvider(native.form.id)
+    nativeFunctionProvider.provideNativeFunction(native.definitions.map { it.text }, node.arguments, slabContext)
   }
 
   private val nativeCached by lazy { resolveMaybeNative() }
@@ -21,7 +21,7 @@ class FunctionContext(val compilationUnitContext: CompilationUnitContext, val no
       return nativeCached!!.call(arguments, stack)
     }
 
-    val scope = compilationUnitContext.internalScope.fork(node.symbol.id)
+    val scope = slabContext.internalScope.fork(node.symbol.id)
     for ((index, spec) in node.arguments.withIndex()) {
       if (spec.multiple) {
         val list = arguments.subList(index, arguments.size - 1)

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

@@ -18,7 +18,7 @@ class InternalNativeProvider(val quiet: Boolean = false) : NativeProvider {
   override fun provideNativeFunction(
     definitions: List<String>,
     arguments: List<ArgumentSpec>,
-    inside: CompilationUnitContext
+    inside: SlabContext
   ): CallableFunction {
     val definition = definitions[0]
     return functions[definition] ?: throw RuntimeException("Unknown Internal Function: $definition")

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

@@ -3,5 +3,5 @@ package gay.pizza.pork.evaluator
 import gay.pizza.pork.ast.gen.ArgumentSpec
 
 interface NativeProvider {
-  fun provideNativeFunction(definitions: List<String>, arguments: List<ArgumentSpec>, inside: CompilationUnitContext): CallableFunction
+  fun provideNativeFunction(definitions: List<String>, arguments: List<ArgumentSpec>, inside: SlabContext): CallableFunction
 }

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

@@ -0,0 +1,62 @@
+package gay.pizza.pork.evaluator
+
+import gay.pizza.pork.ast.gen.Definition
+import gay.pizza.pork.ast.gen.FunctionDefinition
+import gay.pizza.pork.ast.gen.LetDefinition
+import gay.pizza.pork.ast.gen.visit
+import gay.pizza.pork.frontend.Slab
+
+class SlabContext(val slab: Slab, val evaluator: Evaluator, rootScope: Scope) {
+  val internalScope = rootScope.fork("internal ${slab.location.commonFriendlyName}")
+  val externalScope = rootScope.fork("external ${slab.location.commonFriendlyName}")
+
+  init {
+    processAllDefinitions()
+  }
+
+  fun ensureImportedContextsExist() {
+    for (importedSlab in slab.importedSlabs) {
+      evaluator.context(importedSlab)
+    }
+  }
+
+  private var initializedFinalScope = false
+
+  fun finalizeScope() {
+    if (initializedFinalScope) {
+      return
+    }
+    initializedFinalScope = true
+    processFinalImportScopes()
+  }
+
+  private fun processAllDefinitions() {
+    for (definition in slab.compilationUnit.definitions) {
+      processDefinition(definition)
+    }
+  }
+
+  private fun processDefinition(definition: Definition) {
+    val internalValue = definitionValue(definition)
+    internalScope.define(definition.symbol.id, internalValue)
+    if (definition.modifiers.export) {
+      externalScope.define(definition.symbol.id, internalValue)
+    }
+  }
+
+  private fun definitionValue(definition: Definition): Any = when (definition) {
+    is FunctionDefinition -> FunctionContext(this, definition)
+    is LetDefinition -> {
+      EvaluationVisitor(internalScope.fork("let ${definition.symbol.id}"), CallStack())
+        .visit(definition.value)
+    }
+  }
+
+  private fun processFinalImportScopes() {
+    for (importedSlab in slab.importedSlabs) {
+      val importedSlabContext = evaluator.context(importedSlab)
+      importedSlabContext.processFinalImportScopes()
+      internalScope.inherit(importedSlabContext.externalScope)
+    }
+  }
+}

examples/count.pork

@@ -1,9 +1,11 @@
-let count = 5
-
 export func main() {
   var x = 1
-  while x <= count {
-    println(x)
+  while x <= 5 {
+    if x == 3 {
+      println("The value is 3")
+    } else {
+      println("The value is not 3")
+    }
     x++
   }
 }

execution/build.gradle.kts

@@ -0,0 +1,8 @@
+plugins {
+  id("gay.pizza.pork.module")
+}
+
+dependencies {
+  api(project(":frontend"))
+  implementation(project(":common"))
+}

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

@@ -0,0 +1,5 @@
+package gay.pizza.pork.execution
+
+interface ExecutionContext {
+  fun execute()
+}

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

@@ -0,0 +1,8 @@
+package gay.pizza.pork.execution
+
+import gay.pizza.pork.ast.gen.Symbol
+import gay.pizza.pork.frontend.ImportLocator
+
+interface ExecutionContextProvider {
+  fun prepare(importLocator: ImportLocator, entryPointSymbol: Symbol): ExecutionContext
+}

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

@@ -25,7 +25,7 @@ class FfiNativeProvider : NativeProvider {
   override fun provideNativeFunction(
     definitions: List<String>,
     arguments: List<ArgumentSpec>,
-    inside: CompilationUnitContext
+    inside: SlabContext
   ): CallableFunction {
     if (definitions[0] == "internal") {
       val internal = internalFunctions[definitions[1]] ?:
@@ -73,7 +73,7 @@ class FfiNativeProvider : NativeProvider {
     }
   }
 
-  private fun addStructDefs(ffiTypeRegistry: FfiTypeRegistry, types: List<String>, inside: CompilationUnitContext) {
+  private fun addStructDefs(ffiTypeRegistry: FfiTypeRegistry, types: List<String>, inside: SlabContext) {
     for (parameter in types) {
       if (!parameter.startsWith("struct ")) {
         continue

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

@@ -15,5 +15,5 @@ object JavaAutogenContentSource : ContentSource {
     return StringCharSource(content)
   }
 
-  override fun stableContentIdentity(path: String): String = path
+  override fun stableContentPath(path: String): String = path
 }

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

@@ -2,7 +2,7 @@ package gay.pizza.pork.ffi
 
 import gay.pizza.pork.ast.gen.ArgumentSpec
 import gay.pizza.pork.evaluator.CallableFunction
-import gay.pizza.pork.evaluator.CompilationUnitContext
+import gay.pizza.pork.evaluator.SlabContext
 import gay.pizza.pork.evaluator.NativeProvider
 import gay.pizza.pork.evaluator.None
 import java.lang.invoke.MethodHandles
@@ -14,7 +14,7 @@ class JavaNativeProvider : NativeProvider {
   override fun provideNativeFunction(
     definitions: List<String>,
     arguments: List<ArgumentSpec>,
-    inside: CompilationUnitContext
+    inside: SlabContext
   ): CallableFunction {
     val functionDefinition = JavaFunctionDefinition.parse(definitions)
     val javaClass = lookupClass(functionDefinition.type)

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

@@ -4,5 +4,5 @@ import gay.pizza.pork.tokenizer.CharSource
 
 interface ContentSource {
   fun loadAsCharSource(path: String): CharSource
-  fun stableContentIdentity(path: String): String
+  fun stableContentPath(path: String): String
 }

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

@@ -1,7 +1,7 @@
 package gay.pizza.pork.frontend
 
 class DynamicImportSource : ImportSource {
-  private val providers = mutableMapOf<String,ContentSource>()
+  private val providers = mutableMapOf<String, ContentSource>()
 
   override fun provideContentSource(form: String): ContentSource {
     return providers[form] ?:

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

@@ -10,7 +10,7 @@ class FsContentSource(val root: FsPath) : ContentSource {
   override fun loadAsCharSource(path: String): CharSource =
     StringCharSource(asFsPath(path).readString())
 
-  override fun stableContentIdentity(path: String): String =
+  override fun stableContentPath(path: String): String =
     asFsPath(path).fullPathString
 
   private fun asFsPath(path: String): FsPath {

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

@@ -0,0 +1,12 @@
+package gay.pizza.pork.frontend
+
+import gay.pizza.pork.ast.gen.CompilationUnit
+import gay.pizza.pork.frontend.scope.SlabScope
+
+class Slab(val world: World, val location: SourceLocation, val compilationUnit: CompilationUnit) {
+  val importedSlabs: List<Slab> by lazy {
+    world.resolveAllImports(this)
+  }
+
+  val scope: SlabScope by lazy { world.scope.index(this) }
+}

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

@@ -0,0 +1,10 @@
+package gay.pizza.pork.frontend
+
+import gay.pizza.pork.tokenizer.SourceIndex
+
+data class SourceLocation(val form: String, val filePath: String, val index: SourceIndex? = null) {
+  val commonFriendlyName: String by lazy { "$form $filePath" }
+
+  fun withSourceIndex(index: SourceIndex): SourceLocation =
+    SourceLocation(form, filePath, index)
+}

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

@@ -0,0 +1,5 @@
+package gay.pizza.pork.frontend
+
+data class StableSourceKey(val form: String, val path: String) {
+  fun asSourceLocation(): SourceLocation = SourceLocation(form, path)
+}

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

@@ -1,22 +1,25 @@
 package gay.pizza.pork.frontend
 
-import gay.pizza.pork.ast.gen.CompilationUnit
 import gay.pizza.pork.ast.gen.ImportDeclaration
+import gay.pizza.pork.frontend.scope.WorldScope
 import gay.pizza.pork.parser.DiscardNodeAttribution
 import gay.pizza.pork.parser.Parser
 import gay.pizza.pork.tokenizer.Tokenizer
 
 class World(val importSource: ImportSource) {
-  private val internalUnits = mutableMapOf<String, CompilationUnit>()
-  private val importedUnits = mutableMapOf<CompilationUnit, Set<CompilationUnit>>()
+  private val preludeImportLocator = ImportLocator("std", "lang/prelude.pork")
 
-  val units: List<CompilationUnit>
-    get() = internalUnits.values.toList()
+  private val internalSlabs = mutableMapOf<StableSourceKey, Slab>()
 
-  private fun loadOneUnit(importLocator: ImportLocator): CompilationUnit {
+  val slabs: List<Slab>
+    get() = internalSlabs.values.toList()
+
+  val scope: WorldScope by lazy { WorldScope(this) }
+
+  private fun loadOneSlab(importLocator: ImportLocator): Slab {
     val contentSource = pickContentSource(importLocator.form)
-    val stableKey = stableIdentity(importLocator, contentSource = contentSource)
-    val cached = internalUnits[stableKey]
+    val stableKey = stableSourceKey(importLocator, contentSource = contentSource)
+    val cached = internalSlabs[stableKey]
     if (cached != null) {
       return cached
     }
@@ -24,40 +27,39 @@ class World(val importSource: ImportSource) {
     val tokenizer = Tokenizer(charSource)
     val parser = Parser(tokenizer, DiscardNodeAttribution)
     val unit = parser.parseCompilationUnit()
-    internalUnits[stableKey] = unit
-    return unit
+    val slab = Slab(world = this, location = stableKey.asSourceLocation(), compilationUnit = unit)
+    internalSlabs[stableKey] = slab
+    return slab
   }
 
-  private fun resolveAllImports(unit: CompilationUnit): Set<CompilationUnit> {
-    val units = mutableSetOf<CompilationUnit>()
-    for (declaration in unit.declarations.filterIsInstance<ImportDeclaration>()) {
+  internal fun resolveAllImports(slab: Slab): List<Slab> {
+    val slabs = mutableListOf<Slab>()
+    if (slab.location.form != preludeImportLocator.form &&
+      slab.location.filePath != preludeImportLocator.path) {
+      slabs.add(loadOneSlab(preludeImportLocator))
+    }
+    for (declaration in slab.compilationUnit.declarations.filterIsInstance<ImportDeclaration>()) {
       val importPath = declaration.path.components.joinToString("/") { it.id } + ".pork"
       val importLocator = ImportLocator(declaration.form.id, importPath)
-      val importedUnit = loadOneUnit(importLocator)
-      units.add(importedUnit)
+      val importedModule = loadOneSlab(importLocator)
+      slabs.add(importedModule)
     }
-    importedUnits[unit] = units
-    return units
+    return slabs
   }
 
-  fun load(importLocator: ImportLocator): CompilationUnit {
-    val unit = loadOneUnit(importLocator)
-    resolveAllImports(unit)
-    return unit
+  fun load(importLocator: ImportLocator): Slab {
+    return loadOneSlab(importLocator)
   }
 
-  fun importedBy(unit: CompilationUnit): Set<CompilationUnit> =
-    importedUnits[unit] ?: emptySet()
-
   private fun pickContentSource(form: String): ContentSource =
     importSource.provideContentSource(form)
 
-  fun stableIdentity(
+  fun stableSourceKey(
     importLocator: ImportLocator,
     contentSource: ContentSource = pickContentSource(importLocator.form)
-  ): String {
+  ): StableSourceKey {
     val formKey = importLocator.form
-    val stableIdentity = contentSource.stableContentIdentity(importLocator.path)
-    return "[${formKey}][${stableIdentity}]"
+    val stableContentPath = contentSource.stableContentPath(importLocator.path)
+    return StableSourceKey(formKey, stableContentPath)
   }
 }

frontend/src/main/kotlin/gay/pizza/pork/frontend/scope/CompilationUnitScope.kt

@@ -1,36 +0,0 @@
-package gay.pizza.pork.frontend.scope
-
-import gay.pizza.pork.ast.gen.CompilationUnit
-import gay.pizza.pork.ast.gen.Symbol
-
-class CompilationUnitScope(val worldScope: WorldScope, val unit: CompilationUnit) {
-  val externalSymbols = mutableSetOf<ScopeSymbol>()
-  val internalSymbols = mutableSetOf<ScopeSymbol>()
-
-  fun index() {
-    for (definition in unit.definitions) {
-      val scopeSymbol = ScopeSymbol(unit, definition)
-      if (definition.modifiers.export) {
-        externalSymbols.add(scopeSymbol)
-      }
-      internalSymbols.add(scopeSymbol)
-    }
-  }
-
-  fun findInternallyVisibleSymbols(): Set<VisibleScopeSymbol> {
-    val allSymbols = mutableMapOf<Symbol, VisibleScopeSymbol>()
-    val imports = worldScope.world.importedBy(unit)
-    for (import in imports) {
-      val scope = worldScope.index(import)
-      for (importedSymbol in scope.externalSymbols) {
-        allSymbols[importedSymbol.symbol] = VisibleScopeSymbol(unit, importedSymbol)
-      }
-    }
-
-    for (internalSymbol in internalSymbols) {
-      allSymbols[internalSymbol.symbol] = VisibleScopeSymbol(unit, internalSymbol)
-    }
-
-    return allSymbols.values.toSet()
-  }
-}

frontend/src/main/kotlin/gay/pizza/pork/frontend/scope/DefinitionScope.kt

@@ -0,0 +1,21 @@
+package gay.pizza.pork.frontend.scope
+
+import gay.pizza.pork.ast.gen.Definition
+import gay.pizza.pork.ast.gen.Symbol
+import gay.pizza.pork.ast.gen.visit
+
+class DefinitionScope(val slabScope: SlabScope, val definition: Definition) {
+  val usedSymbols: List<ScopeSymbol> by lazy {
+    val symbols = mutableListOf<ScopeSymbol>()
+    val analyzer = ExternalSymbolUsageAnalyzer()
+    analyzer.visit(definition)
+    for (symbol in analyzer.usedSymbols) {
+      val resolved = slabScope.resolve(symbol)
+        ?: throw RuntimeException("Unable to resolve symbol: ${symbol.id}")
+      symbols.add(resolved)
+    }
+    symbols
+  }
+
+  fun resolve(symbol: Symbol): ScopeSymbol? = slabScope.resolve(symbol)
+}

frontend/src/main/kotlin/gay/pizza/pork/frontend/scope/ExternalSymbolUsageAnalyzer.kt

@@ -0,0 +1,135 @@
+package gay.pizza.pork.frontend.scope
+
+import gay.pizza.pork.ast.FunctionLevelVisitor
+import gay.pizza.pork.ast.gen.*
+
+class ExternalSymbolUsageAnalyzer : FunctionLevelVisitor<Unit>() {
+  private val symbols = mutableSetOf<Symbol>()
+  private val internalSymbols = mutableListOf<MutableSet<Symbol>>()
+
+  val usedSymbols: Set<Symbol>
+    get() = symbols
+
+  override fun visitFunctionDefinition(node: FunctionDefinition) {
+    internalSymbols.add(node.arguments.map { it.symbol }.toMutableSet())
+    node.block?.visit(this)
+    internalSymbols.removeLast()
+  }
+
+  override fun visitLetDefinition(node: LetDefinition) {
+    node.value.visit(this)
+  }
+
+  override fun visitBlock(node: Block) {
+    internalSymbols.add(mutableSetOf())
+    node.visitChildren(this)
+    internalSymbols.removeLast()
+  }
+
+  override fun visitBooleanLiteral(node: BooleanLiteral) {
+    node.visitChildren(this)
+  }
+
+  override fun visitBreak(node: Break) {
+    node.visitChildren(this)
+  }
+
+  override fun visitContinue(node: Continue) {
+    node.visitChildren(this)
+  }
+
+  override fun visitDoubleLiteral(node: DoubleLiteral) {
+    node.visitChildren(this)
+  }
+
+  override fun visitForIn(node: ForIn) {
+    node.expression.visit(this)
+    internalSymbols.add(mutableSetOf(node.item.symbol))
+    node.block.visit(this)
+    internalSymbols.removeLast()
+  }
+
+  override fun visitFunctionCall(node: FunctionCall) {
+    checkAndContribute(node.symbol)
+    for (argument in node.arguments) {
+      visit(argument)
+    }
+  }
+
+  override fun visitIf(node: If) {
+    node.condition.visit(this)
+    node.thenBlock.visit(this)
+    node.elseBlock?.visit(this)
+  }
+
+  override fun visitIndexedBy(node: IndexedBy) {
+    node.visitChildren(this)
+  }
+
+  override fun visitInfixOperation(node: InfixOperation) {
+    node.visitChildren(this)
+  }
+
+  override fun visitIntegerLiteral(node: IntegerLiteral) {
+    node.visitChildren(this)
+  }
+
+  override fun visitLetAssignment(node: LetAssignment) {
+    internalSymbols.last().add(node.symbol)
+    node.value.visit(this)
+  }
+
+  override fun visitListLiteral(node: ListLiteral) {
+    node.visitChildren(this)
+  }
+
+  override fun visitLongLiteral(node: LongLiteral) {
+    node.visitChildren(this)
+  }
+
+  override fun visitNoneLiteral(node: NoneLiteral) {
+    node.visitChildren(this)
+  }
+
+  override fun visitParentheses(node: Parentheses) {
+    node.visitChildren(this)
+  }
+
+  override fun visitPrefixOperation(node: PrefixOperation) {
+    node.visitChildren(this)
+  }
+
+  override fun visitSetAssignment(node: SetAssignment) {
+    node.visitChildren(this)
+  }
+
+  override fun visitStringLiteral(node: StringLiteral) {
+    node.visitChildren(this)
+  }
+
+  override fun visitSuffixOperation(node: SuffixOperation) {
+    node.visitChildren(this)
+  }
+
+  override fun visitSymbolReference(node: SymbolReference) {
+    checkAndContribute(node.symbol)
+  }
+
+  override fun visitVarAssignment(node: VarAssignment) {
+    internalSymbols.last().add(node.symbol)
+    node.value.visit(this)
+  }
+
+  override fun visitWhile(node: While) {
+    node.condition.visit(this)
+    internalSymbols.add(mutableSetOf())
+    node.block.visit(this)
+    internalSymbols.removeLast()
+  }
+
+  private fun checkAndContribute(symbol: Symbol) {
+    if (internalSymbols.none { it.contains(symbol) }) {
+      symbols.add(symbol)
+    }
+  }
+}

frontend/src/main/kotlin/gay/pizza/pork/frontend/scope/ScopeSymbol.kt

@@ -1,11 +1,9 @@
 package gay.pizza.pork.frontend.scope
 
 import gay.pizza.pork.ast.gen.Definition
-import gay.pizza.pork.ast.gen.Node
+import gay.pizza.pork.ast.gen.Symbol
 
-class ScopeSymbol(
-  val compilationUnit: Node,
-  val definition: Definition
-) {
-  val symbol = definition.symbol
+class ScopeSymbol(val slabScope: SlabScope, val definition: Definition) {
+  val symbol: Symbol = definition.symbol
+  val scope: DefinitionScope by lazy { DefinitionScope(slabScope, definition) }
 }

frontend/src/main/kotlin/gay/pizza/pork/frontend/scope/SlabScope.kt

@@ -0,0 +1,48 @@
+package gay.pizza.pork.frontend.scope
+
+import gay.pizza.pork.ast.gen.Symbol
+import gay.pizza.pork.frontend.Slab
+
+class SlabScope(val worldScope: WorldScope, val slab: Slab) {
+  private val externalSymbolsList = mutableSetOf<ScopeSymbol>()
+  private val internalSymbolsList = mutableSetOf<ScopeSymbol>()
+
+  val externalSymbols: Set<ScopeSymbol>
+    get() = externalSymbolsList
+
+  val internalSymbols: Set<ScopeSymbol>
+    get() = internalSymbolsList
+
+  val internallyVisibleSymbols: List<VisibleScopeSymbol> by lazy { findInternallyVisibleSymbols() }
+
+  fun index() {
+    for (definition in slab.compilationUnit.definitions) {
+      val scopeSymbol = ScopeSymbol(this, definition)
+      if (definition.modifiers.export) {
+        externalSymbolsList.add(scopeSymbol)
+      }
+      internalSymbolsList.add(scopeSymbol)
+    }
+  }
+
+  private fun findInternallyVisibleSymbols(): List<VisibleScopeSymbol> {
+    val allSymbols = mutableMapOf<Symbol, VisibleScopeSymbol>()
+    val imports = slab.importedSlabs
+    for (import in imports) {
+      val scope = worldScope.index(import)
+      for (importedSymbol in scope.externalSymbols) {
+        allSymbols[importedSymbol.symbol] = VisibleScopeSymbol(slab, importedSymbol)
+      }
+    }
+
+    for (internalSymbol in internalSymbols) {
+      allSymbols[internalSymbol.symbol] = VisibleScopeSymbol(slab, internalSymbol)
+    }
+
+    return allSymbols.values.toList()
+  }
+
+  fun resolve(symbol: Symbol): ScopeSymbol? = internallyVisibleSymbols.firstOrNull {
+    it.scopeSymbol.symbol == symbol
+  }?.scopeSymbol
+}

frontend/src/main/kotlin/gay/pizza/pork/frontend/scope/VisibleScopeSymbol.kt

@@ -1,8 +1,8 @@
 package gay.pizza.pork.frontend.scope
 
-import gay.pizza.pork.ast.gen.CompilationUnit
+import gay.pizza.pork.frontend.Slab
 
-class VisibleScopeSymbol(val visibleToUnit: CompilationUnit, val scopeSymbol: ScopeSymbol) {
+class VisibleScopeSymbol(val visibleToSlab: Slab, val scopeSymbol: ScopeSymbol) {
   val isInternalSymbol: Boolean
-    get() = visibleToUnit == scopeSymbol.compilationUnit
+    get() = visibleToSlab == scopeSymbol.slabScope.slab
 }

frontend/src/main/kotlin/gay/pizza/pork/frontend/scope/WorldScope.kt

@@ -1,24 +1,24 @@
 package gay.pizza.pork.frontend.scope
 
-import gay.pizza.pork.ast.gen.CompilationUnit
 import gay.pizza.pork.frontend.World
+import gay.pizza.pork.frontend.Slab
 
 class WorldScope(val world: World) {
-  private val compilationUnitScopes = mutableMapOf<CompilationUnit, CompilationUnitScope>()
+  private val slabScopes = mutableMapOf<Slab, SlabScope>()
 
   fun indexAll() {
-    for (unit in world.units) {
-      index(unit)
+    for (module in world.slabs) {
+      index(module)
     }
   }
 
-  fun index(unit: CompilationUnit): CompilationUnitScope =
-    scope(unit).apply {
+  fun index(slab: Slab): SlabScope =
+    scope(slab).apply {
       index()
     }
 
-  fun scope(unit: CompilationUnit): CompilationUnitScope =
-    compilationUnitScopes.computeIfAbsent(unit) {
-      CompilationUnitScope(this, unit)
+  fun scope(slab: Slab): SlabScope =
+    slabScopes.computeIfAbsent(slab) {
+      SlabScope(this, slab)
     }
 }

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

@@ -36,16 +36,16 @@ abstract class Tool {
 
   fun <T> visit(visitor: NodeVisitor<T>): T = visitor.visit(parse())
 
-  fun loadMainFunction(scope: Scope, setupEvaluator: Evaluator.() -> Unit = {}): CallableFunction {
+  fun loadMainFunction(setupEvaluator: Evaluator.() -> Unit = {}): CallableFunction {
     val world = buildWorld()
-    val evaluator = Evaluator(world, scope)
+    val evaluator = Evaluator(world)
     setupEvaluator(evaluator)
     val resultingScope = evaluator.evaluate(rootImportLocator)
     return resultingScope.value("main") as CallableFunction
   }
 
-  fun loadMainFunctionStandard(scope: Scope, quiet: Boolean = false): CallableFunction =
-    loadMainFunction(scope, setupEvaluator = {
+  fun loadMainFunctionStandard(quiet: Boolean = false): CallableFunction =
+    loadMainFunction(setupEvaluator = {
       addNativeProvider("internal", InternalNativeProvider(quiet = quiet))
       addNativeProvider("ffi", FfiNativeProvider())
       addNativeProvider("java", JavaNativeProvider())
@@ -60,8 +60,8 @@ abstract class Tool {
     return World(dynamicImportSource)
   }
 
-  fun run(scope: Scope, quiet: Boolean = false) {
-    val main = loadMainFunctionStandard(scope, quiet = quiet)
+  fun run(quiet: Boolean = false) {
+    val main = loadMainFunctionStandard(quiet = quiet)
     main.call(emptyList(), CallStack())
   }
 }

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

@@ -11,5 +11,5 @@ fun main(args: Array<String>) {
   }
   val path = PlatformFsProvider.resolve(args[0])
   val tool = FileTool(path)
-  tool.run(Scope.root())
+  tool.run()
 }

settings.gradle.kts

@@ -6,8 +6,12 @@ include(
   ":common",
   ":tokenizer",
   ":ast",
+  ":bytecode",
   ":parser",
   ":frontend",
+  ":compiler",
+  ":execution",
+  ":vm",
   ":evaluator",
   ":stdlib",
   ":ffi",

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

@@ -34,7 +34,7 @@ object PorkStdlib : ContentSource {
     return StringCharSource(readPorkFile(path))
   }
 
-  override fun stableContentIdentity(path: String): String {
+  override fun stableContentPath(path: String): String {
     return path
   }
 }

stdlib/src/main/pork/ffi/struct.pork

@@ -1,7 +1,7 @@
 export func ffiStructDefine(items...)
   native ffi "internal" "ffiStructDefine"
 
-export func ffiStructAllocate(struct)
+export func ffiStructAllocate(def)
   native ffi "internal" "ffiStructAllocate"
 
 export func ffiStructValue(def, field, value)

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

@@ -76,7 +76,6 @@ enum class TokenType(vararg val properties: TokenTypeProperty) {
   ))),
   BlockComment(CharConsume(MatchedCharConsumer("/*", "*/")), CommentFamily),
   LineComment(CharConsume(MatchedCharConsumer("//", "\n", AllowEofTermination)), CommentFamily),
-  Struct(ManyChars("struct"), KeywordFamily),
   EndOfFile;
 
   val promotions: List<Promotion> =

tool/build.gradle.kts

@@ -7,6 +7,8 @@ plugins {
 
 dependencies {
   api(project(":minimal"))
+  api(project(":compiler"))
+  api(project(":vm"))
   api("com.github.ajalt.clikt:clikt:4.2.0")
 
   implementation(project(":common"))

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

@@ -0,0 +1,33 @@
+package gay.pizza.pork.tool
+
+import com.github.ajalt.clikt.core.CliktCommand
+import com.github.ajalt.clikt.parameters.arguments.argument
+import gay.pizza.dough.fs.PlatformFsProvider
+import gay.pizza.pork.ast.gen.Symbol
+import gay.pizza.pork.compiler.Compiler
+import gay.pizza.pork.minimal.FileTool
+import gay.pizza.pork.vm.VirtualMachine
+
+class CompileCommand : CliktCommand(help = "Compile Pork to Bytecode", name = "compile") {
+  val path by argument("file")
+
+  override fun run() {
+    val tool = FileTool(PlatformFsProvider.resolve(path))
+    val world = tool.buildWorld()
+    val compiler = Compiler()
+    val slab = world.load(tool.rootImportLocator)
+    val compiledSlab = compiler.compilableSlabs.of(slab)
+    val compiledMain = compiledSlab.compilableSymbolOf(Symbol("main"))
+      ?: throw RuntimeException("'main' function not found.")
+    val compiledWorld = compiler.compile(compiledMain)
+    for (symbol in compiledWorld.symbolTable.symbols) {
+      val code = compiledWorld.code.subList(symbol.offset.toInt(), (symbol.offset + symbol.size).toInt())
+      println(symbol.id)
+      for ((index, op) in code.withIndex()) {
+        println("  ${symbol.offset + index.toUInt()} ${op.code.name} ${op.args.joinToString(" ")}")
+      }
+    }
+    val vm = VirtualMachine(compiledWorld)
+    vm.execute()
+  }
+}

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

@@ -17,7 +17,8 @@ class RootCommand : CliktCommand(
       AstCommand(),
       AttributeCommand(),
       ScopeAnalysisCommand(),
-      CopyStdlibCommand()
+      CopyStdlibCommand(),
+      CompileCommand()
     )
   }
 

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

@@ -6,8 +6,6 @@ import com.github.ajalt.clikt.parameters.options.flag
 import com.github.ajalt.clikt.parameters.options.option
 import gay.pizza.dough.fs.PlatformFsProvider
 import gay.pizza.pork.evaluator.*
-import gay.pizza.pork.ffi.FfiNativeProvider
-import gay.pizza.pork.ffi.JavaNativeProvider
 import gay.pizza.pork.minimal.FileTool
 
 class RunCommand : CliktCommand(help = "Run Program", name = "run") {
@@ -19,12 +17,11 @@ class RunCommand : CliktCommand(help = "Run Program", name = "run") {
 
   override fun run() {
     val tool = FileTool(PlatformFsProvider.resolve(path))
-    val scope = Scope.root()
-    val main = tool.loadMainFunctionStandard(scope, quiet = quiet)
+    val main = tool.loadMainFunctionStandard(quiet = quiet)
 
     if (dumpScope) {
       val functionContext = main as FunctionContext
-      val internalScope = functionContext.compilationUnitContext.internalScope
+      val internalScope = functionContext.slabContext.internalScope
       internalScope.crawlScopePath { key, path ->
         println("[scope] $key [${path.joinToString(" -> ")}]")
       }

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

@@ -15,12 +15,12 @@ class ScopeAnalysisCommand : CliktCommand(help = "Run Scope Analysis", name = "s
     val root = world.load(tool.rootImportLocator)
     val scope = WorldScope(world).apply { index(root) }
     val rootScope = scope.scope(root)
-    val visibleScopeSymbols = rootScope.findInternallyVisibleSymbols()
-    for (visibleScopeSymbol in visibleScopeSymbols) {
+    for (visibleScopeSymbol in rootScope.internallyVisibleSymbols) {
       println(
         "symbol ${visibleScopeSymbol.scopeSymbol.symbol.id} " +
         "type=${visibleScopeSymbol.scopeSymbol.definition.type.name} " +
-        "internal=${visibleScopeSymbol.isInternalSymbol}"
+        "internal=${visibleScopeSymbol.isInternalSymbol} " +
+        "slab=${visibleScopeSymbol.scopeSymbol.slab.location.commonFriendlyName}"
       )
     }
   }

vm/build.gradle.kts

@@ -0,0 +1,11 @@
+plugins {
+  id("gay.pizza.pork.module")
+}
+
+dependencies {
+  api(project(":execution"))
+  api(project(":bytecode"))
+  api(project(":compiler"))
+
+  implementation(project(":common"))
+}

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

@@ -0,0 +1,80 @@
+package gay.pizza.pork.vm
+
+import gay.pizza.pork.bytecode.CompiledWorld
+
+class InternalMachine(val world: CompiledWorld, val handlers: List<OpHandler>) {
+  private val inlined = world.code.map { op ->
+    val handler = handlers.firstOrNull { it.code == op.code } ?:
+      throw VirtualMachineException("Opcode ${op.code.name} does not have a handler.")
+    op to handler
+  }
+
+  private var inst: UInt = 0u
+  private val stack = mutableListOf<Any>(EndOfCode)
+  private val locals = mutableListOf<MutableMap<UInt, Any>>(
+    mutableMapOf()
+  )
+  private var autoNextInst = true
+  private var exitFlag = false
+
+  fun step(): Boolean {
+    val (op, handler) = inlined[inst.toInt()]
+    handler.handle(this, op)
+    if (autoNextInst) {
+      inst++
+    }
+    autoNextInst = true
+    return !exitFlag
+  }
+
+  fun pushScope() {
+    locals.add(mutableMapOf())
+  }
+
+  fun popScope() {
+    locals.removeLast()
+  }
+
+  fun loadConstant(id: UInt) {
+    push(world.constantPool.constants[id.toInt()])
+  }
+
+  fun loadLocal(id: UInt) {
+    val localSet = locals.last()
+    val local = localSet[id]
+      ?: throw VirtualMachineException("Attempted to load local $id but it was not stored.")
+    push(local)
+  }
+
+  fun storeLocal(id: UInt) {
+    val localSet = locals.last()
+    val value = pop()
+    localSet[id] = value
+  }
+
+  fun setNextInst(value: UInt) {
+    inst = value
+    autoNextInst = false
+  }
+
+  fun push(item: Any) {
+    stack.add(item)
+  }
+
+  fun pop(): Any = stack.removeLast()
+  fun exit() {
+    exitFlag = true
+  }
+
+  fun reset() {
+    stack.clear()
+    stack.add(EndOfCode)
+    locals.clear()
+    locals.add(mutableMapOf())
+    inst = 0u
+    exitFlag = false
+    autoNextInst = true
+  }
+
+  data object EndOfCode
+}

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

@@ -0,0 +1,8 @@
+package gay.pizza.pork.vm
+
+import gay.pizza.pork.bytecode.Op
+import gay.pizza.pork.bytecode.Opcode
+
+abstract class OpHandler(val code: Opcode) {
+  abstract fun handle(machine: InternalMachine, op: Op)
+}

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

@@ -0,0 +1,45 @@
+package gay.pizza.pork.vm
+
+import gay.pizza.pork.bytecode.CompiledWorld
+import gay.pizza.pork.execution.ExecutionContext
+import gay.pizza.pork.vm.ops.*
+
+class VirtualMachine(world: CompiledWorld) : ExecutionContext {
+  private val internal = InternalMachine(world, listOf(
+    IntegerOpHandler,
+    ConstantOpHandler,
+
+    TrueOpHandler,
+    FalseOpHandler,
+
+    ListOpHandler,
+
+    CompareEqualOpHandler,
+    CompareLesserEqualOpHandler,
+
+    AddOpHandler,
+
+    JumpOpHandler,
+    JumpIfOpHandler,
+
+    LoadLocalOpHandler,
+    StoreLocalOpHandler,
+
+    CallOpHandler,
+    RetOpHandler,
+
+    NativeOpHandler,
+
+    ScopeInOpHandler,
+    ScopeOutOpHandler
+  ))
+
+  override fun execute() {
+    while (true) {
+      if (!internal.step()) {
+        break
+      }
+    }
+    internal.reset()
+  }
+}

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

@@ -0,0 +1,3 @@
+package gay.pizza.pork.vm
+
+class VirtualMachineException(message: String) : RuntimeException(message)

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

@@ -0,0 +1,20 @@
+package gay.pizza.pork.vm
+
+import gay.pizza.pork.ast.gen.Symbol
+import gay.pizza.pork.compiler.Compiler
+import gay.pizza.pork.execution.ExecutionContext
+import gay.pizza.pork.execution.ExecutionContextProvider
+import gay.pizza.pork.frontend.ImportLocator
+import gay.pizza.pork.frontend.World
+
+class VirtualMachineProvider(val world: World) : ExecutionContextProvider {
+  override fun prepare(importLocator: ImportLocator, entryPointSymbol: Symbol): ExecutionContext {
+    val compiler = Compiler()
+    val slab = world.load(importLocator)
+    val compilableSlab = compiler.compilableSlabs.of(slab)
+    val compilableSymbol = compilableSlab.compilableSymbolOf(entryPointSymbol) ?:
+      throw RuntimeException("Unable to find compilable symbol for entry point '${entryPointSymbol.id}'")
+    val compiledWorld = compiler.compile(compilableSymbol)
+    return VirtualMachine(compiledWorld)
+  }
+}

vm/src/main/kotlin/gay/pizza/pork/vm/ops/AddOpHandler.kt

@@ -0,0 +1,19 @@
+package gay.pizza.pork.vm.ops
+
+import gay.pizza.pork.bytecode.Op
+import gay.pizza.pork.bytecode.Opcode
+import gay.pizza.pork.vm.InternalMachine
+import gay.pizza.pork.vm.OpHandler
+import gay.pizza.pork.vm.VirtualMachineException
+
+object AddOpHandler : OpHandler(Opcode.Add) {
+  override fun handle(machine: InternalMachine, op: Op) {
+    val left = machine.pop()
+    val right = machine.pop()
+
+    if (left !is Int || right !is Int) {
+      throw VirtualMachineException("Bad types.")
+    }
+    machine.push(left + right)
+  }
+}

vm/src/main/kotlin/gay/pizza/pork/vm/ops/CallOpHandler.kt

@@ -0,0 +1,13 @@
+package gay.pizza.pork.vm.ops
+
+import gay.pizza.pork.bytecode.Op
+import gay.pizza.pork.bytecode.Opcode
+import gay.pizza.pork.vm.InternalMachine
+import gay.pizza.pork.vm.OpHandler
+
+object CallOpHandler : OpHandler(Opcode.Call) {
+  override fun handle(machine: InternalMachine, op: Op) {
+    machine.setNextInst(op.args[0])
+    machine.pushScope()
+  }
+}

vm/src/main/kotlin/gay/pizza/pork/vm/ops/CompareEqualOpHandler.kt

@@ -0,0 +1,12 @@
+package gay.pizza.pork.vm.ops
+
+import gay.pizza.pork.bytecode.Op
+import gay.pizza.pork.bytecode.Opcode
+import gay.pizza.pork.vm.InternalMachine
+import gay.pizza.pork.vm.OpHandler
+
+object CompareEqualOpHandler : OpHandler(Opcode.CompareEqual) {
+  override fun handle(machine: InternalMachine, op: Op) {
+    machine.push(machine.pop() == machine.pop())
+  }
+}

vm/src/main/kotlin/gay/pizza/pork/vm/ops/CompareLesserEqualOpHandler.kt

@@ -0,0 +1,19 @@
+package gay.pizza.pork.vm.ops
+
+import gay.pizza.pork.bytecode.Op
+import gay.pizza.pork.bytecode.Opcode
+import gay.pizza.pork.vm.InternalMachine
+import gay.pizza.pork.vm.OpHandler
+import gay.pizza.pork.vm.VirtualMachineException
+
+object CompareLesserEqualOpHandler : OpHandler(Opcode.CompareLesserEqual) {
+  override fun handle(machine: InternalMachine, op: Op) {
+    val right = machine.pop()
+    val left = machine.pop()
+
+    if (left !is Int || right !is Int) {
+      throw VirtualMachineException("Bad types.")
+    }
+    machine.push(left <= right)
+  }
+}

vm/src/main/kotlin/gay/pizza/pork/vm/ops/ConstantOpHandler.kt

@@ -0,0 +1,12 @@
+package gay.pizza.pork.vm.ops
+
+import gay.pizza.pork.bytecode.Op
+import gay.pizza.pork.bytecode.Opcode
+import gay.pizza.pork.vm.InternalMachine
+import gay.pizza.pork.vm.OpHandler
+
+object ConstantOpHandler : OpHandler(Opcode.Constant) {
+  override fun handle(machine: InternalMachine, op: Op) {
+    machine.loadConstant(op.args[0])
+  }
+}

vm/src/main/kotlin/gay/pizza/pork/vm/ops/FalseOpHandler.kt

@@ -0,0 +1,12 @@
+package gay.pizza.pork.vm.ops
+
+import gay.pizza.pork.bytecode.Op
+import gay.pizza.pork.bytecode.Opcode
+import gay.pizza.pork.vm.InternalMachine
+import gay.pizza.pork.vm.OpHandler
+
+object FalseOpHandler : OpHandler(Opcode.False) {
+  override fun handle(machine: InternalMachine, op: Op) {
+    machine.push(false)
+  }
+}

vm/src/main/kotlin/gay/pizza/pork/vm/ops/IntegerOpHandler.kt

@@ -0,0 +1,12 @@
+package gay.pizza.pork.vm.ops
+
+import gay.pizza.pork.bytecode.Op
+import gay.pizza.pork.bytecode.Opcode
+import gay.pizza.pork.vm.InternalMachine
+import gay.pizza.pork.vm.OpHandler
+
+object IntegerOpHandler : OpHandler(Opcode.Integer) {
+  override fun handle(machine: InternalMachine, op: Op) {
+    machine.push(op.args[0].toInt())
+  }
+}

vm/src/main/kotlin/gay/pizza/pork/vm/ops/JumpIfOpHandler.kt

@@ -0,0 +1,20 @@
+package gay.pizza.pork.vm.ops
+
+import gay.pizza.pork.bytecode.Op
+import gay.pizza.pork.bytecode.Opcode
+import gay.pizza.pork.vm.InternalMachine
+import gay.pizza.pork.vm.OpHandler
+import gay.pizza.pork.vm.VirtualMachineException
+
+object JumpIfOpHandler : OpHandler(Opcode.JumpIf) {
+  override fun handle(machine: InternalMachine, op: Op) {
+    val value = machine.pop()
+    if (value !is Boolean) {
+      throw VirtualMachineException("JumpIf expects a boolean value on the stack.")
+    }
+
+    if (value) {
+      machine.setNextInst(op.args[0])
+    }
+  }
+}

vm/src/main/kotlin/gay/pizza/pork/vm/ops/JumpOpHandler.kt

@@ -0,0 +1,12 @@
+package gay.pizza.pork.vm.ops
+
+import gay.pizza.pork.bytecode.Op
+import gay.pizza.pork.bytecode.Opcode
+import gay.pizza.pork.vm.InternalMachine
+import gay.pizza.pork.vm.OpHandler
+
+object JumpOpHandler : OpHandler(Opcode.Jump) {
+  override fun handle(machine: InternalMachine, op: Op) {
+    machine.setNextInst(op.args[0])
+  }
+}

vm/src/main/kotlin/gay/pizza/pork/vm/ops/ListOpHandler.kt

@@ -0,0 +1,18 @@
+package gay.pizza.pork.vm.ops
+
+import gay.pizza.pork.bytecode.Op
+import gay.pizza.pork.bytecode.Opcode
+import gay.pizza.pork.vm.InternalMachine
+import gay.pizza.pork.vm.OpHandler
+
+object ListOpHandler : OpHandler(Opcode.List) {
+  override fun handle(machine: InternalMachine, op: Op) {
+    val count = op.args[0]
+    val list = mutableListOf<Any>()
+    for (i in 1u..count) {
+      val item = machine.pop()
+      list.add(item)
+    }
+    machine.push(list.reversed())
+  }
+}

vm/src/main/kotlin/gay/pizza/pork/vm/ops/LoadLocalOpHandler.kt

@@ -0,0 +1,12 @@
+package gay.pizza.pork.vm.ops
+
+import gay.pizza.pork.bytecode.Op
+import gay.pizza.pork.bytecode.Opcode
+import gay.pizza.pork.vm.InternalMachine
+import gay.pizza.pork.vm.OpHandler
+
+object LoadLocalOpHandler : OpHandler(Opcode.LoadLocal) {
+  override fun handle(machine: InternalMachine, op: Op) {
+    machine.loadLocal(op.args[0])
+  }
+}

vm/src/main/kotlin/gay/pizza/pork/vm/ops/NativeOpHandler.kt

@@ -0,0 +1,16 @@
+package gay.pizza.pork.vm.ops
+
+import gay.pizza.pork.bytecode.Op
+import gay.pizza.pork.bytecode.Opcode
+import gay.pizza.pork.vm.InternalMachine
+import gay.pizza.pork.vm.OpHandler
+
+object NativeOpHandler : OpHandler(Opcode.Native) {
+  override fun handle(machine: InternalMachine, op: Op) {
+    val countOfNativeDefs = op.args[1].toInt()
+    val defs = mutableListOf<Any>()
+    for (i in 0 until countOfNativeDefs) {
+      defs.add(String(machine.pop() as ByteArray))
+    }
+  }
+}

vm/src/main/kotlin/gay/pizza/pork/vm/ops/RetOpHandler.kt

@@ -0,0 +1,18 @@
+package gay.pizza.pork.vm.ops
+
+import gay.pizza.pork.bytecode.Op
+import gay.pizza.pork.bytecode.Opcode
+import gay.pizza.pork.vm.InternalMachine
+import gay.pizza.pork.vm.OpHandler
+
+object RetOpHandler : OpHandler(Opcode.Return) {
+  override fun handle(machine: InternalMachine, op: Op) {
+    val last = machine.pop()
+    if (last == InternalMachine.EndOfCode) {
+      machine.exit()
+      return
+    }
+    machine.popScope()
+    machine.setNextInst((last as Int).toUInt())
+  }
+}

vm/src/main/kotlin/gay/pizza/pork/vm/ops/ScopeInOpHandler.kt

@@ -0,0 +1,10 @@
+package gay.pizza.pork.vm.ops
+
+import gay.pizza.pork.bytecode.Op
+import gay.pizza.pork.bytecode.Opcode
+import gay.pizza.pork.vm.InternalMachine
+import gay.pizza.pork.vm.OpHandler
+
+object ScopeInOpHandler : OpHandler(Opcode.ScopeIn) {
+  override fun handle(machine: InternalMachine, op: Op) {}
+}

vm/src/main/kotlin/gay/pizza/pork/vm/ops/ScopeOutOpHandler.kt

@@ -0,0 +1,10 @@
+package gay.pizza.pork.vm.ops
+
+import gay.pizza.pork.bytecode.Op
+import gay.pizza.pork.bytecode.Opcode
+import gay.pizza.pork.vm.InternalMachine
+import gay.pizza.pork.vm.OpHandler
+
+object ScopeOutOpHandler : OpHandler(Opcode.ScopeOut) {
+  override fun handle(machine: InternalMachine, op: Op) {}
+}

vm/src/main/kotlin/gay/pizza/pork/vm/ops/StoreLocalOpHandler.kt

@@ -0,0 +1,12 @@
+package gay.pizza.pork.vm.ops
+
+import gay.pizza.pork.bytecode.Op
+import gay.pizza.pork.bytecode.Opcode
+import gay.pizza.pork.vm.InternalMachine
+import gay.pizza.pork.vm.OpHandler
+
+object StoreLocalOpHandler : OpHandler(Opcode.StoreLocal) {
+  override fun handle(machine: InternalMachine, op: Op) {
+    machine.storeLocal(op.args[0])
+  }
+}

vm/src/main/kotlin/gay/pizza/pork/vm/ops/TrueOpHandler.kt

@@ -0,0 +1,12 @@
+package gay.pizza.pork.vm.ops
+
+import gay.pizza.pork.bytecode.Op
+import gay.pizza.pork.bytecode.Opcode
+import gay.pizza.pork.vm.InternalMachine
+import gay.pizza.pork.vm.OpHandler
+
+object TrueOpHandler : OpHandler(Opcode.True) {
+  override fun handle(machine: InternalMachine, op: Op) {
+    machine.push(true)
+  }
+}