implement read functions on emptyenv

com.oracle.truffle.r.runtime/src/com/oracle/truffle/r/runtime/env/REnvironment.java

@@ -1037,12 +1037,11 @@ public abstract class REnvironment extends RAttributeStorage implements RTypedVa
     }
 
     /**
-     * The empty environment has no runtime state and so can be allocated statically. TODO Attempts
-     * to assign should cause an R error, if not prevented in caller. TODO check.
+     * The empty environment has no runtime state and so can be allocated statically.
      */
     private static final class Empty extends REnvironment {
 
-        public final static String EMPTY_ENV_NAME = "R_EmptyEnv";
+        public static final String EMPTY_ENV_NAME = "R_EmptyEnv";
 
         private Empty() {
             super(null, EMPTY_ENV_NAME, new REnvEmptyFrameAccess());

com.oracle.truffle.r.runtime/src/com/oracle/truffle/r/runtime/env/frame/REnvEmptyFrameAccess.java

@@ -31,6 +31,7 @@ import com.oracle.truffle.r.runtime.env.*;
 import com.oracle.truffle.r.runtime.env.REnvironment.*;
 
 public final class REnvEmptyFrameAccess extends REnvFrameAccess {
+    private static final RStringVector EMPTY = RDataFactory.createEmptyStringVector();
 
     @Override
     public MaterializedFrame getFrame() {
@@ -39,7 +40,7 @@ public final class REnvEmptyFrameAccess extends REnvFrameAccess {
 
     @Override
     public Object get(String key) {
-        throw RInternalError.shouldNotReachHere();
+        return null;
     }
 
     @Override
@@ -49,12 +50,12 @@ public final class REnvEmptyFrameAccess extends REnvFrameAccess {
 
     @Override
     public void rm(String key) throws PutException {
-        throw RInternalError.shouldNotReachHere();
+        throw new PutException(RError.Message.UNKNOWN_OBJECT, key);
     }
 
     @Override
     public RStringVector ls(boolean allNames, Pattern pattern, boolean sorted) {
-        throw RInternalError.shouldNotReachHere();
+        return EMPTY;
     }
 
     @Override