Split out all code into modules.

frontend/build.gradle.kts

@@ -0,0 +1,10 @@
+plugins {
+  pork_module
+}
+
+dependencies {
+  api(project(":ast"))
+  api(project(":parser"))
+
+  implementation(project(":common"))
+}

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

@@ -0,0 +1,8 @@
+package gay.pizza.pork.frontend
+
+import gay.pizza.pork.parser.CharSource
+
+interface ContentSource {
+  fun loadAsCharSource(path: String): CharSource
+  fun stableContentIdentity(path: String): String
+}

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

@@ -0,0 +1,23 @@
+package gay.pizza.pork.frontend
+
+import gay.pizza.pork.parser.StringCharSource
+import java.nio.file.Path
+import kotlin.io.path.absolutePathString
+import kotlin.io.path.readText
+
+class FsContentSource(val root: Path) : ContentSource {
+  override fun loadAsCharSource(path: String): gay.pizza.pork.parser.CharSource =
+    StringCharSource(asFsPath(path).readText())
+
+  override fun stableContentIdentity(path: String): String =
+    asFsPath(path).absolutePathString()
+
+  private fun asFsPath(path: String): Path {
+    val fsPath = root.resolve(path)
+    val absoluteRootPath = root.absolutePathString() + root.fileSystem.separator
+    if (!fsPath.absolutePathString().startsWith(absoluteRootPath)) {
+      throw RuntimeException("Unable to load path outside of the root: $fsPath (root is ${root})")
+    }
+    return fsPath
+  }
+}

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

@@ -0,0 +1,41 @@
+package gay.pizza.pork.frontend
+
+import gay.pizza.pork.ast.CompilationUnit
+import gay.pizza.pork.ast.ImportDeclaration
+import gay.pizza.pork.parser.Parser
+import gay.pizza.pork.parser.TokenStreamSource
+import gay.pizza.pork.parser.Tokenizer
+
+class World(val contentSource: ContentSource) {
+  private val units = mutableMapOf<String, CompilationUnit>()
+
+  private fun loadOneUnit(path: String): CompilationUnit {
+    val stableIdentity = contentSource.stableContentIdentity(path)
+    val cached = units[stableIdentity]
+    if (cached != null) {
+      return cached
+    }
+    val charSource = contentSource.loadAsCharSource(path)
+    val tokenizer = Tokenizer(charSource)
+    val tokenStream = tokenizer.tokenize()
+    val parser = Parser(TokenStreamSource(tokenStream), gay.pizza.pork.parser.DiscardNodeAttribution)
+    return parser.readCompilationUnit()
+  }
+
+  private fun resolveAllImports(unit: CompilationUnit): Set<CompilationUnit> {
+    val units = mutableSetOf<CompilationUnit>()
+    for (declaration in unit.declarations.filterIsInstance<ImportDeclaration>()) {
+      val importedUnit = loadOneUnit(declaration.path.text)
+      units.add(importedUnit)
+    }
+    return units
+  }
+
+  fun load(path: String): CompilationUnit {
+    val unit = loadOneUnit(path)
+    resolveAllImports(unit)
+    return unit
+  }
+
+  fun units(path: String): Set<CompilationUnit> = resolveAllImports(loadOneUnit(path))
+}