Minor cleanup.

src/main/scala/lexi/Compiler.scala

@@ -4,7 +4,7 @@ import lexi.ir.nodes.IrTree
 import lexi.ir.phases.IrAnalysis
 
 case class Compiler(
-  var context: Context = new Context
+  context: Context = new Context
 ) {
   def run(sources: Vector[Source]): Vector[CompilationUnit] =
     sources.map(CompilationUnit(_))

src/main/scala/lexi/Language.scala

@@ -6,9 +6,9 @@ enum Language(value: String) {
 }
 
 object Language {
-  def withFileType(fileType: String): Language =
-    fileType match {
-      case "kt" => Kotlin
-      case "scala" => Scala
-    }
+  def withFileType(fileType: String): Either[Throwable, Language] = fileType match {
+    case "kt" => Right(Kotlin)
+    case "scala" => Right(Scala)
+    case _ => Left(Exception("Unable to determine language for the file type."))
+  }
 }

src/main/scala/lexi/Source.scala

@@ -14,24 +14,24 @@ case class Source(
 
 object Source {
   def fromFile(file: String): Either[Throwable, Source] =
-    Try(Files.readString(Path.of(file))).toEither match {
-      case Right(content) =>
-        Right(
-          Source(
-            file = file,
-            text = content,
-            language = languageFromFile(file)
-          )
-        )
-      case Left(exception) => Left(exception)
-    }
+    for {
+      language <- fileLanguage(file)
+      content  <- readFile(file)
+    } yield Source(
+      file = file,
+      text = content,
+      language = language
+    )
 
   def fromString(source: String, language: Language): Source =
     new Source(file = null, text = source, language = language)
 
-  def languageFromFile(file: String): Language =
+  def fileLanguage(file: String): Either[Throwable, Language] =
     Language.withFileType(getFileExtension(file))
 
+  def readFile(file: String): Either[Throwable, String] =
+    Try(Files.readString(Path.of(file))).toEither
+
   private def getFileExtension(file: String): String =
     file.substring(file.lastIndexOf('.') + 1)
 }