Start writing the REPL in Wren.

It doesn't actually execute code yet, but it:

- Supports left and right arrow keys for moving the cursor.
- Ctrl-C, Ctrl-D, Ctrl-A, and Ctrl-E for navigating.
- Syntax highlights the line (!).

The next step is to do a rough parse so that we can tell if the line
is an expression, statement, or needs more input. That will tell us
whether we need to interpret it at the top level (statement) and not
worry about a result, evaluate it as an expression and print the result,
or read more lines.

src/cli/modules.c

@@ -5,6 +5,7 @@
 
 #include "io.wren.inc"
 #include "os.wren.inc"
+#include "repl.wren.inc"
 #include "scheduler.wren.inc"
 #include "timer.wren.inc"
 
@@ -162,6 +163,8 @@ static ModuleRegistry modules[] =
       STATIC_METHOD("allArguments", processAllArguments)
     END_CLASS
   END_MODULE
+  MODULE(repl)
+  END_MODULE
   MODULE(scheduler)
     CLASS(Scheduler)
       STATIC_METHOD("captureMethods_()", schedulerCaptureMethods)

src/cli/vm.c

@@ -6,8 +6,6 @@
 #include "scheduler.h"
 #include "vm.h"
 
-#define MAX_LINE_LENGTH 1024 // TODO: Something less arbitrary.
-
 // The single VM instance that the CLI uses.
 static WrenVM* vm;
 
@@ -259,23 +257,9 @@ int runRepl()
   printf("\\\\/\"-\n");
   printf(" \\_/   wren v%s\n", WREN_VERSION_STRING);
 
-  char line[MAX_LINE_LENGTH];
-
-  for (;;)
-  {
-    printf("> ");
-
-    if (!fgets(line, MAX_LINE_LENGTH, stdin))
-    {
-      printf("\n");
-      break;
-    }
-
-    // TODO: Handle failure.
-    wrenInterpret(vm, line);
-
-    // TODO: Automatically print the result of expressions.
-  }
+  wrenInterpret(vm, "import \"repl\"\n");
+  
+  uv_run(loop, UV_RUN_DEFAULT);
 
   freeVM();