diff --git a/com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/fastr/FastRInterop.java b/com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/fastr/FastRInterop.java
index 335338ad4e1d64314b62dfff57eafe05c474f622..e1cc075cb7b0ca5506a25df67b4dc46925e77106 100644
--- a/com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/fastr/FastRInterop.java
+++ b/com.oracle.truffle.r.nodes.builtin/src/com/oracle/truffle/r/nodes/builtin/fastr/FastRInterop.java
@@ -255,6 +255,11 @@ public class FastRInterop {
         public byte isNull(TruffleObject obj) {
             return RRuntime.asLogical(ForeignAccess.sendIsNull(node, obj));
         }
+
+        @Fallback
+        public byte isNull(Object obj) {
+            return RRuntime.asLogical(false);
+        }
     }
 
     @RBuiltin(name = "is.external.executable", visibility = ON, kind = PRIMITIVE, parameterNames = {"value"}, behavior = COMPLEX)
@@ -270,6 +275,11 @@ public class FastRInterop {
         public byte isExecutable(TruffleObject obj) {
             return RRuntime.asLogical(ForeignAccess.sendIsExecutable(node, obj));
         }
+
+        @Fallback
+        public byte isExecutable(Object obj) {
+            return RRuntime.asLogical(false);
+        }
     }
 
     @RBuiltin(name = "as.external.byte", visibility = ON, kind = PRIMITIVE, parameterNames = {"value"}, behavior = COMPLEX)
diff --git a/com.oracle.truffle.r.pkgs/graalvm/R/g.R b/com.oracle.truffle.r.pkgs/graalvm/R/g.R
index a39bb05199fd0a4c31a0846d32d718849cca4537..6be25c8445ae89aac701b3d6efc633e5dc4bc18f 100644
--- a/com.oracle.truffle.r.pkgs/graalvm/R/g.R
+++ b/com.oracle.truffle.r.pkgs/graalvm/R/g.R
@@ -337,7 +337,9 @@ sendAttempt <- function(code, echo, mimetype) {
 	
 	if (resp$status_code >= 400) {
 		stop(respObj)
-	} else {
+	} else if (echo) {
 		respObj
+	} else {
+		invisible(NULL)
 	}
 }
diff --git a/com.oracle.truffle.r.pkgs/graalvm/R/graalvm.R b/com.oracle.truffle.r.pkgs/graalvm/R/graalvm.R
index 2c6c4b66e7195f7e6c09c8bb991b06269e8a5044..74bcf413033c89b656bc37935fc79dfa33e4f80e 100644
--- a/com.oracle.truffle.r.pkgs/graalvm/R/graalvm.R
+++ b/com.oracle.truffle.r.pkgs/graalvm/R/graalvm.R
@@ -6,21 +6,20 @@
 #' # Loading and setting up
 #' 
 #' library(graalvm)
-#' graalvm.setup("~/work/graalvm-0.21")
+#' graalvm.setup("~/work/graalvm-0.25")
 #' 
 #' # Code execution
-#' g(v <- runif(1e8))
+#' g(v <- runif(1e3))
 #' g(f <- function(x) { s <- 0; for (i in seq_along(x)) s <- s + x[[i]]; s })
 #' g(system.time(f(v)))
-#' g(system.time(f(v)))
 #' 
 #' g.js("1 < 2")
 #' g.rb("$a = 2")
 #' 
 #' 
-#' # Paired variables
+#' # Coupled variables
 #' 
-#' # Create and initialize paired variables:
+#' # Create and initialize coupled variables:
 #' gset.r(a1, TRUE) 
 #' gset.js(a2, c(1,2))
 #' gset.rb(a3, list(a=1,b="2")) 
@@ -32,17 +31,18 @@
 #' g.rb("$a3")
 #' 
 #' g(a1 <- FALSE)
+#' # Sync the local a1 with the remote a1
 #' gget(a1)
 #' a1
 #' 
-#' # Paired functions
+#' # Coupled functions
 #' 
-#' # Create a paired function
+#' # Create a coupled function
 #' gset.r(measure, function(n) { system.time(runif(n)) })
-#' # Execute the local version of the paired function
+#' # Execute the local version of the coupled function
 #' measure(1e8)
-#' # Execute the remote version of the paired function
-#' g(measure(1e8))
+#' # Execute the remote version of the coupled function
+#' g(measure(1e8)) # Try a couple of times
 #' 
 #' # Executing a script file
 #' 
diff --git a/com.oracle.truffle.r.pkgs/graalvm/man/graalvm.Rd b/com.oracle.truffle.r.pkgs/graalvm/man/graalvm.Rd
index 96c0d86c24f63bc09feff2103b15a36d0111a6cb..b37a22e7112cb28b6f85221c38e54abe9433e908 100644
--- a/com.oracle.truffle.r.pkgs/graalvm/man/graalvm.Rd
+++ b/com.oracle.truffle.r.pkgs/graalvm/man/graalvm.Rd
@@ -12,21 +12,20 @@ of GraalVM to GNUR users.
 # Loading and setting up
 
 library(graalvm)
-graalvm.setup("~/work/graalvm-0.21")
+graalvm.setup("~/work/graalvm-0.25")
 
 # Code execution
-g(v <- runif(1e8))
+g(v <- runif(1e3))
 g(f <- function(x) { s <- 0; for (i in seq_along(x)) s <- s + x[[i]]; s })
 g(system.time(f(v)))
-g(system.time(f(v)))
 
 g.js("1 < 2")
 g.rb("$a = 2")
 
 
-# Paired variables
+# Coupled variables
 
-# Create and initialize paired variables:
+# Create and initialize coupled variables:
 gset.r(a1, TRUE) 
 gset.js(a2, c(1,2))
 gset.rb(a3, list(a=1,b="2")) 
@@ -38,17 +37,18 @@ g.js("a2")
 g.rb("$a3")
 
 g(a1 <- FALSE)
+# Sync the local a1 with the remote a1
 gget(a1)
 a1
 
-# Paired functions
+# Coupled functions
 
-# Create a paired function
+# Create a coupled function
 gset.r(measure, function(n) { system.time(runif(n)) })
-# Execute the local version of the paired function
+# Execute the local version of the coupled function
 measure(1e8)
-# Execute the remote version of the paired function
-g(measure(1e8))
+# Execute the remote version of the coupled function
+g(measure(1e8)) # Try a couple of times
 
 # Executing a script file
 
diff --git a/com.oracle.truffle.r.test/src/com/oracle/truffle/r/test/ExpectedTestOutput.test b/com.oracle.truffle.r.test/src/com/oracle/truffle/r/test/ExpectedTestOutput.test
index ac34216e446012ba1f06857ec4b2c129855479e1..24f399344e17ce51fdbcd358552f47acc586395b 100644
--- a/com.oracle.truffle.r.test/src/com/oracle/truffle/r/test/ExpectedTestOutput.test
+++ b/com.oracle.truffle.r.test/src/com/oracle/truffle/r/test/ExpectedTestOutput.test
@@ -130825,6 +130825,42 @@ Error in eval.external(, "abc", ) : invalid mimeType argument
 ##com.oracle.truffle.r.test.library.fastr.TestInterop.testInteropExport#
 #if (!any(R.version$engine == "FastR")) { invisible() } else { export('foo', new.env()) }
 
+##com.oracle.truffle.r.test.library.fastr.TestInterop.testIsExternalExecutable#
+#if (!any(R.version$engine == "FastR")) { FALSE } else { is.external.executable() }
+[1] FALSE
+
+##com.oracle.truffle.r.test.library.fastr.TestInterop.testIsExternalExecutable#
+#if (!any(R.version$engine == "FastR")) { FALSE } else { is.external.executable(NULL) }
+[1] FALSE
+
+##com.oracle.truffle.r.test.library.fastr.TestInterop.testIsExternalExecutable#
+#if (!any(R.version$engine == "FastR")) { FALSE } else { is.external.executable(c(1)) }
+[1] FALSE
+
+##com.oracle.truffle.r.test.library.fastr.TestInterop.testIsExternalExecutable#
+#if (!any(R.version$engine == "FastR")) { FALSE } else { is.external.executable(list(1)) }
+[1] FALSE
+
+##com.oracle.truffle.r.test.library.fastr.TestInterop.testIsExternalExecutable#
+#if (!any(R.version$engine == "FastR")) { TRUE } else { is.external.executable(sum) }
+[1] TRUE
+
+##com.oracle.truffle.r.test.library.fastr.TestInterop.testIsExternalNull#
+#if (!any(R.version$engine == "FastR")) { FALSE } else { is.external.null() }
+[1] FALSE
+
+##com.oracle.truffle.r.test.library.fastr.TestInterop.testIsExternalNull#
+#if (!any(R.version$engine == "FastR")) { FALSE } else { is.external.null(c(1)) }
+[1] FALSE
+
+##com.oracle.truffle.r.test.library.fastr.TestInterop.testIsExternalNull#
+#if (!any(R.version$engine == "FastR")) { FALSE } else { is.external.null(list(1)) }
+[1] FALSE
+
+##com.oracle.truffle.r.test.library.fastr.TestInterop.testIsExternalNull#
+#if (!any(R.version$engine == "FastR")) { TRUE } else { is.external.null(NULL) }
+[1] TRUE
+
 ##com.oracle.truffle.r.test.library.fastr.TestInterop.testPrinting#
 #if (!any(R.version$engine == "FastR")) { c('intValue', 'longValue', 'charValue', 'shortValue', 'booleanValue', 'stringValue') } else { v <- import('testPOJO'); names(v) }
 [1] "intValue"     "longValue"    "charValue"    "shortValue"   "booleanValue"
@@ -132901,7 +132937,7 @@ In if (c(T, F)) print("OK") :
 #if (!any(R.version$engine == "FastR")) { 'abc' } else { tc <- new.java.class('java.lang.String'); t <- new.external(tc, 'abc'); t }
 [1] "abc"
 
-##com.oracle.truffle.r.test.library.fastr.TestJavaInterop.testInteroptNew#
+##com.oracle.truffle.r.test.library.fastr.TestJavaInterop.testInteroptNew#Ignored.Unknown#
 #if (!any(R.version$engine == "FastR")) { 'truffle.object' } else { tc <- new.java.class('com.oracle.truffle.r.test.library.fastr.TestJavaInterop$TestNullClass'); t <- new.external(tc, NULL); class(t) }
 [1] "truffle.object"
 
@@ -132937,6 +132973,30 @@ In if (c(T, F)) print("OK") :
 #if (!any(R.version$engine == "FastR")) { TRUE } else { tc <- new.java.class('java/lang/Boolean'); t <- new(tc, TRUE); t }
 [1] TRUE
 
+##com.oracle.truffle.r.test.library.fastr.TestJavaInterop.testIsExternalExecutable#
+#if (!any(R.version$engine == "FastR")) { FALSE } else { to <- new.external(new.java.class('com.oracle.truffle.r.test.library.fastr.TestJavaInterop$TestClass'));is.external.executable(to$fieldBoolean) }
+[1] FALSE
+
+##com.oracle.truffle.r.test.library.fastr.TestJavaInterop.testIsExternalExecutable#
+#if (!any(R.version$engine == "FastR")) { FALSE } else { to <- new.external(new.java.class('com.oracle.truffle.r.test.library.fastr.TestJavaInterop$TestClass'));is.external.executable(to) }
+[1] FALSE
+
+##com.oracle.truffle.r.test.library.fastr.TestJavaInterop.testIsExternalExecutable#
+#if (!any(R.version$engine == "FastR")) { TRUE } else { to <- new.external(new.java.class('com.oracle.truffle.r.test.library.fastr.TestJavaInterop$TestClass'));is.external.executable(to$methodBoolean) }
+[1] TRUE
+
+##com.oracle.truffle.r.test.library.fastr.TestJavaInterop.testIsExternalNull#
+#if (!any(R.version$engine == "FastR")) { FALSE } else { to <- new.external(new.java.class('com.oracle.truffle.r.test.library.fastr.TestJavaInterop$TestClass'));is.external.null(to$methodReturnsNull) }
+[1] FALSE
+
+##com.oracle.truffle.r.test.library.fastr.TestJavaInterop.testIsExternalNull#
+#if (!any(R.version$engine == "FastR")) { FALSE } else { to <- new.external(new.java.class('com.oracle.truffle.r.test.library.fastr.TestJavaInterop$TestClass'));is.external.null(to) }
+[1] FALSE
+
+##com.oracle.truffle.r.test.library.fastr.TestJavaInterop.testIsExternalNull#
+#if (!any(R.version$engine == "FastR")) { TRUE } else { to <- new.external(new.java.class('com.oracle.truffle.r.test.library.fastr.TestJavaInterop$TestClass'));is.external.null(to$methodReturnsNull()) }
+[1] TRUE
+
 ##com.oracle.truffle.r.test.library.fastr.TestJavaInterop.testIsXXXForForeignObject#
 #if (!any(R.version$engine == "FastR")) { FALSE } else { to <- new.external(new.java.class('com.oracle.truffle.r.test.library.fastr.TestJavaInterop$TestClass')); is.array(to) }
 [1] FALSE
diff --git a/com.oracle.truffle.r.test/src/com/oracle/truffle/r/test/library/fastr/TestInterop.java b/com.oracle.truffle.r.test/src/com/oracle/truffle/r/test/library/fastr/TestInterop.java
index ea7ba39d215c9b70769ddd65a781c6fafd61bf6a..42a8a05bd16b6282d4ef61e0e1e0f64b30b8caf3 100644
--- a/com.oracle.truffle.r.test/src/com/oracle/truffle/r/test/library/fastr/TestInterop.java
+++ b/com.oracle.truffle.r.test/src/com/oracle/truffle/r/test/library/fastr/TestInterop.java
@@ -66,6 +66,23 @@ public class TestInterop extends TestBase {
         assertEvalFastR("export('foo', new.env())", "invisible()");
     }
 
+    @Test
+    public void testIsExternalExecutable() {
+        assertEvalFastR("is.external.executable(sum)", "TRUE");
+        assertEvalFastR("is.external.executable(NULL)", "FALSE");
+        assertEvalFastR("is.external.executable(c(1))", "FALSE");
+        assertEvalFastR("is.external.executable(list(1))", "FALSE");
+        assertEvalFastR("is.external.executable()", "FALSE");
+    }
+
+    @Test
+    public void testIsExternalNull() {
+        assertEvalFastR("is.external.null(NULL)", "TRUE");
+        assertEvalFastR("is.external.null(c(1))", "FALSE");
+        assertEvalFastR("is.external.null(list(1))", "FALSE");
+        assertEvalFastR("is.external.null()", "FALSE");
+    }
+
     @Test
     public void testInteropEvalFile() {
         assertEvalFastR("fileConn<-file(\"" + TEST_EVAL_FILE + "\");writeLines(c(\"x<-c(1)\",\"cat(x)\"), fileConn);close(fileConn);eval.external(mimeType=\"application/x-r\", path=\"" +
diff --git a/com.oracle.truffle.r.test/src/com/oracle/truffle/r/test/library/fastr/TestJavaInterop.java b/com.oracle.truffle.r.test/src/com/oracle/truffle/r/test/library/fastr/TestJavaInterop.java
index 6ac5634afde57abf29bc2ace4d80fa77dac4f8e5..f54c7aabf0b8f9089112d23b22bc8957e1514924 100644
--- a/com.oracle.truffle.r.test/src/com/oracle/truffle/r/test/library/fastr/TestJavaInterop.java
+++ b/com.oracle.truffle.r.test/src/com/oracle/truffle/r/test/library/fastr/TestJavaInterop.java
@@ -427,6 +427,20 @@ public class TestJavaInterop extends TestBase {
         assertEvalFastR(Ignored.ImplementationError, "tc <- new.java.class('" + TestNamesClassMap.class.getName() + "'); to <- new.external(tc); sort(names(to$m()))", "c('one', 'two')");
     }
 
+    @Test
+    public void testIsExternalExecutable() {
+        assertEvalFastR(CREATE_TRUFFLE_OBJECT + "is.external.executable(to)", "FALSE");
+        assertEvalFastR(CREATE_TRUFFLE_OBJECT + "is.external.executable(to$methodBoolean)", "TRUE");
+        assertEvalFastR(CREATE_TRUFFLE_OBJECT + "is.external.executable(to$fieldBoolean)", "FALSE");
+    }
+
+    @Test
+    public void testIsExternalNull() {
+        assertEvalFastR(CREATE_TRUFFLE_OBJECT + "is.external.null(to)", "FALSE");
+        assertEvalFastR(CREATE_TRUFFLE_OBJECT + "is.external.null(to$methodReturnsNull)", "FALSE");
+        assertEvalFastR(CREATE_TRUFFLE_OBJECT + "is.external.null(to$methodReturnsNull())", "TRUE");
+    }
+
     @Test
     public void testIsXXXForForeignObject() {
         // missing: is.element, is.empty.model, is.leaf, is.loaded, is.na.data.frame,