Merge pull request #7 from kevinvandervlist/jline

Add Jline ('readline') to the REPL for convenience

Author: kevinvandervlist

README.md

@@ -7,7 +7,7 @@ This provides a parser and interpreter and REPL for the untyped lambda calculus.
 The REPL has tracing capabilities to show all intermediate reduction steps.
 Among others, the following features are supported:
 
-* Lambda is either a `λ` or a `\ `, so `\x.x` and `λx.x` are identical.
+* Lambda is either a `λ` or a `\\ `, so `\\x.x` and `λx.x` are identical.
 * There is a shorthand available for nesting, so `λx y z.x y z` is equal to `λx.λy.λz.x y z`.
 * The parser is fully left-associative, so `x y z` is `(x y) z`.
 * The REPL can toggle between a normal and a *tracing* mode, showing all intermediate reduction steps.

build.sbt

@@ -57,7 +57,8 @@ lazy val repl = (project in file("repl")).
     libraryDependencies ++= Seq(
       "org.scala-lang.modules" %% "scala-parser-combinators" % sParSecVersion,
       "org.typelevel" %% "cats" % catsVersion,
-      "org.typelevel" %% "cats-free" % catsVersion
+      "org.typelevel" %% "cats-free" % catsVersion,
+      "org.jline" % "jline" % "3.1.2"
     ),
     mainClass in assembly := Some("nl.soqua.lcpi.repl.Main")
   ).dependsOn(ast, parser, interpreter % "test->test;compile->compile")

repl/src/main/scala/nl/soqua/lcpi/repl/Main.scala

@@ -6,46 +6,48 @@ import nl.soqua.lcpi.interpreter.Context
 import nl.soqua.lcpi.repl.lib.{CombinatorLibrary, DiskIO}
 import nl.soqua.lcpi.repl.monad.{ReplCompiler, ReplState}
 import nl.soqua.lcpi.repl.parser.StdInParser
+import org.jline.reader.LineReaderBuilder
+import org.jline.terminal.TerminalBuilder
 
 import scala.io.Source
 import scala.util.Try
 
 object Main extends App {
   var ctx = CombinatorLibrary loadIn Context()
 
-  def drawShell(): Unit = print("lcpi λ> ")
+  val prompt = "lcpi λ> "
 
   println(
     """
       |A λ-calculus interpreter. Type `help` for usage information.
     """.stripMargin
   )
 
-  drawShell()
-
   var state = ReplState.empty
   var effect: Any = _
 
+  val terminal = TerminalBuilder.builder()
+    .system(true)
+    .build()
+
+  val lineReader = LineReaderBuilder.builder()
+    .terminal(terminal)
+    .build()
+
   val compiler = new DiskIO() with ReplCompiler {
     override def readFile(path: String): Try[Stream[String]] = Try {
       Source.fromFile(new File(path)).getLines().toStream
     }
   }
 
-  for (ln <- io.Source.stdin.getLines) {
-    StdInParser(ln) match {
+  while (!state.terminated) {
+    val line = Try(lineReader.readLine(prompt)).getOrElse("quit")
+    StdInParser(line) match {
       case Left(e) => println(e)
-      case Right(cmd) => cmd.foldMap(compiler.compile).run(state).value match {
-        case (s: ReplState, _) if s.terminated =>
-          System.exit(0)
-        case (s: ReplState, effect: String) =>
-          state = s
-          println(effect)
-        case (s: ReplState, _) =>
-          state = s
-        case _ =>
+      case Right(cmd) => state = cmd.foldMap(compiler.compile).run(state).value match {
+        case (s: ReplState, effect: String) => println(effect); s
+        case (s: ReplState, _) => s
       }
     }
-    drawShell()
   }
 }

repl/src/main/scala/nl/soqua/lcpi/repl/Messages.scala

@@ -13,7 +13,7 @@ object Messages {
   val help: String =
     s"""
       |Notation:
-      |* λ is either a λ or a \\. So both \\x.x and λx.x are allowed.
+      |* λ is either a λ or a \\\\. So both \\\\x.x and λx.x are allowed.
       |* You can assign variables; `I := λx.x` stores the identity function to the variable `I`.
       |  These have to be capitalized.
       |