--- a/truffle/com.oracle.truffle.sl.test/src/com/oracle/truffle/sl/test/SLTckTest.java	Wed Sep 09 18:53:14 2015 +0200
+++ b/truffle/com.oracle.truffle.sl.test/src/com/oracle/truffle/sl/test/SLTckTest.java	Wed Sep 09 19:18:44 2015 +0200
@@ -152,4 +152,12 @@
     @Override
     public void testPlusWithFloat() throws Exception {
     }
+
+    @Override
+    public void testPrimitiveReturnTypeDouble() throws Exception {
+    }
+
+    @Override
+    public void testPrimitiveReturnTypeFloat() throws Exception {
+    }
 }

--- a/truffle/com.oracle.truffle.sl/src/com/oracle/truffle/sl/nodes/call/SLInvokeNode.java	Wed Sep 09 18:53:14 2015 +0200
+++ b/truffle/com.oracle.truffle.sl/src/com/oracle/truffle/sl/nodes/call/SLInvokeNode.java	Wed Sep 09 19:18:44 2015 +0200
@@ -110,6 +110,7 @@
         if (crossLanguageCall == null) {
             crossLanguageCall = insert(Message.createExecute(argumentValues.length).createNode());
         }
-        return ForeignAccess.execute(crossLanguageCall, frame, function, argumentValues);
+        Object res = ForeignAccess.execute(crossLanguageCall, frame, function, argumentValues);
+        return SLContext.fromForeignValue(res);
     }
 }

--- a/truffle/com.oracle.truffle.sl/src/com/oracle/truffle/sl/runtime/SLContext.java	Wed Sep 09 18:53:14 2015 +0200
+++ b/truffle/com.oracle.truffle.sl/src/com/oracle/truffle/sl/runtime/SLContext.java	Wed Sep 09 19:18:44 2015 +0200
@@ -53,6 +53,7 @@
 import com.oracle.truffle.sl.nodes.*;
 import com.oracle.truffle.sl.nodes.local.*;
 import com.oracle.truffle.sl.parser.*;
+import java.math.BigInteger;
 
 /**
  * The run-time state of SL during execution. One context is instantiated before any source code is
@@ -198,4 +199,13 @@
     public static DynamicObject castSLObject(Object value) {
         return LAYOUT.getType().cast(value);
     }
+
+    public static Object fromForeignValue(Object a) {
+        if (a instanceof Long || a instanceof BigInteger) {
+            return a;
+        } else if (a instanceof Number) {
+            return ((Number) a).longValue();
+        }
+        return a;
+    }
 }

--- a/truffle/com.oracle.truffle.sl/src/com/oracle/truffle/sl/runtime/SLFunctionForeignAccess.java	Wed Sep 09 18:53:14 2015 +0200
+++ b/truffle/com.oracle.truffle.sl/src/com/oracle/truffle/sl/runtime/SLFunctionForeignAccess.java	Wed Sep 09 19:18:44 2015 +0200
@@ -49,7 +49,7 @@
 import com.oracle.truffle.sl.SLLanguage;
 import com.oracle.truffle.sl.nodes.call.SLDispatchNode;
 import com.oracle.truffle.sl.nodes.call.SLDispatchNodeGen;
-import java.math.BigInteger;
+import static com.oracle.truffle.sl.runtime.SLContext.fromForeignValue;
 import java.util.List;
 
 /**
@@ -102,20 +102,10 @@
                 arr = args.toArray();
             }
             for (int i = 0; i < arr.length; i++) {
-                Object a = arr[i];
-                if (a instanceof Long) {
-                    continue;
-                }
-                if (a instanceof BigInteger) {
-                    continue;
-                }
-                if (a instanceof Number) {
-                    arr[i] = ((Number) a).longValue();
-                }
+                arr[i] = fromForeignValue(arr[i]);
             }
             return dispatch.executeDispatch(frame, function, arr);
         }
-
     }
 
     private static class SLForeignNullCheckNode extends RootNode {

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/truffle/com.oracle.truffle.tck/src/com/oracle/truffle/tck/ConstantFunction.java	Wed Sep 09 19:18:44 2015 +0200
@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2015, 2015, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package com.oracle.truffle.tck;
+
+final class ConstantFunction implements ObjectBinaryOperation {
+    private final Object constant;
+
+    public ConstantFunction(Object constant) {
+        this.constant = constant;
+    }
+
+    @Override
+    public Object compute(Object ignore1, Object ignore2) {
+        return constant;
+    }
+}

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/truffle/com.oracle.truffle.tck/src/com/oracle/truffle/tck/ObjectBinaryOperation.java	Wed Sep 09 19:18:44 2015 +0200
@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2015, 2015, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package com.oracle.truffle.tck;
+
+/**
+ * Binary operation on any objects. Mimics "functional interface" - e.g. has just a single method,
+ * so it should be easily usable with lamdas.
+ */
+public interface ObjectBinaryOperation {
+    Object compute(Object a, Object b);
+}

--- a/truffle/com.oracle.truffle.tck/src/com/oracle/truffle/tck/TruffleTCK.java	Wed Sep 09 18:53:14 2015 +0200
+++ b/truffle/com.oracle.truffle.tck/src/com/oracle/truffle/tck/TruffleTCK.java	Wed Sep 09 19:18:44 2015 +0200
@@ -347,6 +347,72 @@
     }
 
     @Test
+    public void testPrimitiveReturnTypeByte() throws Exception {
+        TruffleVM.Symbol apply = findGlobalSymbol(applyNumbers());
+
+        byte value = (byte) RANDOM.nextInt(100);
+
+        TruffleObject fn = JavaInterop.asTruffleFunction(ObjectBinaryOperation.class, new ConstantFunction(value));
+        Number n = apply.invoke(null, fn).as(Number.class);
+        assertEquals("The same value returned", value + 10, n.byteValue());
+    }
+
+    @Test
+    public void testPrimitiveReturnTypeShort() throws Exception {
+        TruffleVM.Symbol apply = findGlobalSymbol(applyNumbers());
+
+        short value = (short) RANDOM.nextInt(100);
+
+        TruffleObject fn = JavaInterop.asTruffleFunction(ObjectBinaryOperation.class, new ConstantFunction(value));
+        Number n = apply.invoke(null, fn).as(Number.class);
+        assertEquals("The same value returned", value + 10, n.shortValue());
+    }
+
+    @Test
+    public void testPrimitiveReturnTypeInt() throws Exception {
+        TruffleVM.Symbol apply = findGlobalSymbol(applyNumbers());
+
+        int value = RANDOM.nextInt(100);
+
+        TruffleObject fn = JavaInterop.asTruffleFunction(ObjectBinaryOperation.class, new ConstantFunction(value));
+        Number n = apply.invoke(null, fn).as(Number.class);
+        assertEquals("The same value returned", value + 10, n.intValue());
+    }
+
+    @Test
+    public void testPrimitiveReturnTypeLong() throws Exception {
+        TruffleVM.Symbol apply = findGlobalSymbol(applyNumbers());
+
+        long value = RANDOM.nextInt(1000);
+
+        TruffleObject fn = JavaInterop.asTruffleFunction(ObjectBinaryOperation.class, new ConstantFunction(value));
+        Number n = apply.invoke(null, fn).as(Number.class);
+        assertEquals("The same value returned", value + 10, n.longValue());
+    }
+
+    @Test
+    public void testPrimitiveReturnTypeFloat() throws Exception {
+        TruffleVM.Symbol apply = findGlobalSymbol(applyNumbers());
+
+        float value = RANDOM.nextInt(1000) + RANDOM.nextFloat();
+
+        TruffleObject fn = JavaInterop.asTruffleFunction(ObjectBinaryOperation.class, new ConstantFunction(value));
+        Number n = apply.invoke(null, fn).as(Number.class);
+        assertEquals("The same value returned", value + 10, n.floatValue(), 0.01);
+    }
+
+    @Test
+    public void testPrimitiveReturnTypeDouble() throws Exception {
+        TruffleVM.Symbol apply = findGlobalSymbol(applyNumbers());
+
+        double value = RANDOM.nextInt(1000) + RANDOM.nextDouble();
+
+        TruffleObject fn = JavaInterop.asTruffleFunction(ObjectBinaryOperation.class, new ConstantFunction(value));
+        Number n = apply.invoke(null, fn).as(Number.class);
+        assertEquals("The same value returned", value + 10, n.doubleValue(), 0.01);
+    }
+
+    @Test
     public void testCoExistanceOfMultipleLanguageInstances() throws Exception {
         final String countMethod = countInvocations();
         TruffleVM.Symbol count1 = findGlobalSymbol(countMethod);