Split out CmdRepl and editorFor

The REPL itself and the `nix repl` CLI are conceptually different
things, and thus deserve to be in different files.

src/libcmd/repl.hh

@@ -0,0 +1,39 @@
+#pragma once
+
+#include "eval.hh"
+
+#if HAVE_BOEHMGC
+#define GC_INCLUDE_NEW
+#include <gc/gc_cpp.h>
+#endif
+
+namespace nix {
+
+struct AbstractNixRepl
+{
+    ref<EvalState> state;
+    Bindings * autoArgs;
+
+    AbstractNixRepl(ref<EvalState> state)
+        : state(state)
+    { }
+
+    virtual ~AbstractNixRepl()
+    { }
+
+    typedef std::vector<std::pair<Value*,std::string>> AnnotatedValues;
+
+    static std::unique_ptr<AbstractNixRepl> create(
+        const Strings & searchPath, nix::ref<Store> store, ref<EvalState> state,
+        std::function<AnnotatedValues()> getValues);
+
+    static void runSimple(
+        ref<EvalState> evalState,
+        const ValMap & extraEnv);
+
+    virtual void initEnv() = 0;
+
+    virtual void mainLoop() = 0;
+};
+
+}