diff --git a/src/main/java/org/rumbledb/api/Item.java b/src/main/java/org/rumbledb/api/Item.java
index 01d5f3f270..c1e790e7be 100644
--- a/src/main/java/org/rumbledb/api/Item.java
+++ b/src/main/java/org/rumbledb/api/Item.java
@@ -439,6 +439,15 @@ default public RuntimeIterator getBodyIterator() {
         throw new UnsupportedOperationException("Operation not defined for type " + this.getDynamicType());
     }
 
+    /**
+     * Returns the body iterator, if it is a function item.
+     * 
+     * @return the function signature.
+     */
+    default public Map<Long, RuntimeIterator> getBodyIterators() {
+        throw new UnsupportedOperationException("Operation not defined for type " + this.getDynamicType());
+    }
+
     /**
      * Returns the local variable bindings, if it is a function item.
      * 
diff --git a/src/main/java/org/rumbledb/compiler/RuntimeIteratorVisitor.java b/src/main/java/org/rumbledb/compiler/RuntimeIteratorVisitor.java
index 35417fd49d..876d9f6c2f 100644
--- a/src/main/java/org/rumbledb/compiler/RuntimeIteratorVisitor.java
+++ b/src/main/java/org/rumbledb/compiler/RuntimeIteratorVisitor.java
@@ -142,6 +142,7 @@
 import org.rumbledb.types.SequenceType;
 
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
@@ -497,12 +498,15 @@ public RuntimeIterator visitInlineFunctionExpr(InlineFunctionExpression expressi
             paramNameToSequenceTypes.put(paramEntry.getKey(), paramEntry.getValue());
         }
         SequenceType returnType = expression.getReturnType();
-        RuntimeIterator bodyIterator = this.visit(expression.getBody(), argument);
+        Map<Long, RuntimeIterator> bodyIterators = new HashMap<>();
+        for (long l : expression.getBodies().keySet()) {
+            bodyIterators.put(l, this.visit(expression.getBodies().get(l), argument));
+        }
         RuntimeIterator runtimeIterator = new FunctionRuntimeIterator(
                 expression.getName(),
                 paramNameToSequenceTypes,
                 returnType,
-                bodyIterator,
+                bodyIterators,
                 expression.getHighestExecutionMode(this.visitorConfig),
                 expression.getMetadata()
         );
diff --git a/src/main/java/org/rumbledb/compiler/StaticContextVisitor.java b/src/main/java/org/rumbledb/compiler/StaticContextVisitor.java
index 3d95657546..bb87b2ea12 100644
--- a/src/main/java/org/rumbledb/compiler/StaticContextVisitor.java
+++ b/src/main/java/org/rumbledb/compiler/StaticContextVisitor.java
@@ -24,6 +24,7 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Map.Entry;
 
 import org.rumbledb.context.BuiltinFunctionCatalogue;
 import org.rumbledb.context.FunctionIdentifier;
@@ -191,23 +192,45 @@ public StaticContext visitFunctionDeclaration(FunctionDeclaration declaration, S
     @Override
     public StaticContext visitInlineFunctionExpr(InlineFunctionExpression expression, StaticContext argument) {
         // define a static context for the function body, add params to the context and visit the body expression
-        StaticContext functionDeclarationContext = new StaticContext(argument);
-        expression.getParams()
-            .forEach(
-                (paramName, sequenceType) -> functionDeclarationContext.addVariable(
-                    paramName,
-                    sequenceType,
-                    expression.getMetadata(),
-                    ExecutionMode.LOCAL
-                )
+        StaticContext functionDeclarationContextLocal = new StaticContext(argument);
+        for (Entry<Name, SequenceType> entry : expression.getParams().entrySet()) {
+            functionDeclarationContextLocal.addVariable(
+                entry.getKey(),
+                entry.getValue(),
+                expression.getMetadata(),
+                ExecutionMode.LOCAL
             );
+        }
         // visit the body first to make its execution mode available while adding the function to the catalog
-        this.visit(expression.getBody(), functionDeclarationContext);
+        this.visit(expression.getBodies().get(0L), functionDeclarationContextLocal);
+
+        StaticContext functionDeclarationContextRDD = new StaticContext(argument);
+        boolean first = true;
+        for (Entry<Name, SequenceType> entry : expression.getParams().entrySet()) {
+            if (first) {
+                functionDeclarationContextRDD.addVariable(
+                    entry.getKey(),
+                    entry.getValue(),
+                    expression.getMetadata(),
+                    ExecutionMode.DATAFRAME
+                );
+                first = false;
+            } else {
+                functionDeclarationContextRDD.addVariable(
+                    entry.getKey(),
+                    entry.getValue(),
+                    expression.getMetadata(),
+                    ExecutionMode.LOCAL
+                );
+            }
+        }
+        StaticContext functionDeclarationContextDF = new StaticContext(argument);
+        this.visit(expression.getBodies().get(1L), functionDeclarationContextDF);
         expression.initHighestExecutionMode(this.visitorConfig);
         expression.registerUserDefinedFunctionExecutionMode(
             this.visitorConfig
         );
-        return functionDeclarationContext;
+        return argument;
     }
 
     @Override
diff --git a/src/main/java/org/rumbledb/compiler/TranslationVisitor.java b/src/main/java/org/rumbledb/compiler/TranslationVisitor.java
index f39e9e2ed7..b7037fbcd6 100644
--- a/src/main/java/org/rumbledb/compiler/TranslationVisitor.java
+++ b/src/main/java/org/rumbledb/compiler/TranslationVisitor.java
@@ -396,7 +396,7 @@ public Name parseName(JsoniqParser.QnameContext ctx, boolean isFunction, boolean
     @Override
     public Node visitFunctionDecl(JsoniqParser.FunctionDeclContext ctx) {
         Name name = parseName(ctx.qname(), true, false);
-        Map<Name, SequenceType> fnParams = new LinkedHashMap<>();
+        LinkedHashMap<Name, SequenceType> fnParams = new LinkedHashMap<>();
         SequenceType fnReturnType = null;
         Name paramName;
         SequenceType paramType;
@@ -1371,7 +1371,7 @@ public Node visitNamedFunctionRef(JsoniqParser.NamedFunctionRefContext ctx) {
 
     @Override
     public Node visitInlineFunctionExpr(JsoniqParser.InlineFunctionExprContext ctx) {
-        Map<Name, SequenceType> fnParams = new LinkedHashMap<>();
+        LinkedHashMap<Name, SequenceType> fnParams = new LinkedHashMap<>();
         SequenceType fnReturnType = SequenceType.MOST_GENERAL_SEQUENCE_TYPE;
         Name paramName;
         SequenceType paramType;
diff --git a/src/main/java/org/rumbledb/compiler/VariableDependenciesVisitor.java b/src/main/java/org/rumbledb/compiler/VariableDependenciesVisitor.java
index 5b3cf524b5..e0dd59a8d7 100644
--- a/src/main/java/org/rumbledb/compiler/VariableDependenciesVisitor.java
+++ b/src/main/java/org/rumbledb/compiler/VariableDependenciesVisitor.java
@@ -352,7 +352,9 @@ public Void visitContextExpr(ContextItemExpression expression, Void argument) {
 
     @Override
     public Void visitInlineFunctionExpr(InlineFunctionExpression expression, Void argument) {
-        visit(expression.getBody(), null);
+        for (long l : expression.getBodies().keySet()) {
+            visit(expression.getBodies().get(l), null);
+        }
         addInputVariableDependencies(expression, getInputVariableDependencies(expression.getBody()));
         removeInputVariableDependencies(expression, expression.getParams().keySet());
         return null;
diff --git a/src/main/java/org/rumbledb/compiler/XQueryTranslationVisitor.java b/src/main/java/org/rumbledb/compiler/XQueryTranslationVisitor.java
index 37b20ce65d..c76066b4c4 100644
--- a/src/main/java/org/rumbledb/compiler/XQueryTranslationVisitor.java
+++ b/src/main/java/org/rumbledb/compiler/XQueryTranslationVisitor.java
@@ -371,7 +371,7 @@ private void processAnnotations(XQueryParser.AnnotationsContext annotations) {
     @Override
     public Node visitFunctionDecl(XQueryParser.FunctionDeclContext ctx) {
         Name name = parseName(ctx.eqName(), true, false);
-        Map<Name, SequenceType> fnParams = new LinkedHashMap<>();
+        LinkedHashMap<Name, SequenceType> fnParams = new LinkedHashMap<>();
         SequenceType fnReturnType = MOST_GENERAL_SEQUENCE_TYPE;
         Name paramName;
         SequenceType paramType;
@@ -1279,7 +1279,7 @@ public Node visitNamedFunctionRef(XQueryParser.NamedFunctionRefContext ctx) {
 
     @Override
     public Node visitInlineFunctionRef(XQueryParser.InlineFunctionRefContext ctx) {
-        Map<Name, SequenceType> fnParams = new LinkedHashMap<>();
+        LinkedHashMap<Name, SequenceType> fnParams = new LinkedHashMap<>();
         SequenceType fnReturnType = SequenceType.MOST_GENERAL_SEQUENCE_TYPE;
         Name paramName;
         SequenceType paramType;
diff --git a/src/main/java/org/rumbledb/expressions/CommaExpression.java b/src/main/java/org/rumbledb/expressions/CommaExpression.java
index 8bebe5e981..8143244050 100644
--- a/src/main/java/org/rumbledb/expressions/CommaExpression.java
+++ b/src/main/java/org/rumbledb/expressions/CommaExpression.java
@@ -29,6 +29,8 @@
 
 public class CommaExpression extends Expression {
 
+    private static final long serialVersionUID = 1L;
+
     private final List<Expression> expressions;
 
     public CommaExpression(List<Expression> expressions, ExceptionMetadata metadata) {
diff --git a/src/main/java/org/rumbledb/expressions/Expression.java b/src/main/java/org/rumbledb/expressions/Expression.java
index 9cc6c5529d..c4d5d2700e 100644
--- a/src/main/java/org/rumbledb/expressions/Expression.java
+++ b/src/main/java/org/rumbledb/expressions/Expression.java
@@ -36,7 +36,8 @@
  */
 public abstract class Expression extends Node {
 
-    protected StaticContext staticContext;
+    private static final long serialVersionUID = 1L;
+    protected transient StaticContext staticContext;
 
     protected SequenceType inferredSequenceType;
 
diff --git a/src/main/java/org/rumbledb/expressions/Node.java b/src/main/java/org/rumbledb/expressions/Node.java
index 4105b8b561..6a1d5f839f 100644
--- a/src/main/java/org/rumbledb/expressions/Node.java
+++ b/src/main/java/org/rumbledb/expressions/Node.java
@@ -24,6 +24,7 @@
 import org.rumbledb.exceptions.ExceptionMetadata;
 import org.rumbledb.exceptions.OurBadException;
 
+import java.io.Serializable;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.function.Predicate;
@@ -32,8 +33,9 @@
  * This is the top-level class for nodes in the intermediate representation of a
  * JSONiq query. Nodes include expressions, clauses, function declarations, etc.
  */
-public abstract class Node {
+public abstract class Node implements Serializable {
 
+    private static final long serialVersionUID = 1L;
     private ExceptionMetadata metadata;
 
     protected ExecutionMode highestExecutionMode = ExecutionMode.UNSET;
diff --git a/src/main/java/org/rumbledb/expressions/arithmetic/AdditiveExpression.java b/src/main/java/org/rumbledb/expressions/arithmetic/AdditiveExpression.java
index c99b7c2f85..babb758e19 100644
--- a/src/main/java/org/rumbledb/expressions/arithmetic/AdditiveExpression.java
+++ b/src/main/java/org/rumbledb/expressions/arithmetic/AdditiveExpression.java
@@ -30,6 +30,8 @@
 import java.util.List;
 
 public class AdditiveExpression extends Expression {
+    private static final long serialVersionUID = 1L;
+
     private Expression leftExpression;
     private Expression rightExpression;
     private boolean isMinus;
diff --git a/src/main/java/org/rumbledb/expressions/arithmetic/MultiplicativeExpression.java b/src/main/java/org/rumbledb/expressions/arithmetic/MultiplicativeExpression.java
index 16423c5a59..50ea315305 100644
--- a/src/main/java/org/rumbledb/expressions/arithmetic/MultiplicativeExpression.java
+++ b/src/main/java/org/rumbledb/expressions/arithmetic/MultiplicativeExpression.java
@@ -31,6 +31,7 @@
 import java.util.List;
 
 public class MultiplicativeExpression extends Expression {
+    private static final long serialVersionUID = 1L;
 
     public static enum MultiplicativeOperator {
         MUL("*"),
diff --git a/src/main/java/org/rumbledb/expressions/comparison/ComparisonExpression.java b/src/main/java/org/rumbledb/expressions/comparison/ComparisonExpression.java
index 4525c5d4a0..b507ba8c2e 100644
--- a/src/main/java/org/rumbledb/expressions/comparison/ComparisonExpression.java
+++ b/src/main/java/org/rumbledb/expressions/comparison/ComparisonExpression.java
@@ -31,6 +31,8 @@
 
 public class ComparisonExpression extends Expression {
 
+    private static final long serialVersionUID = 1L;
+
     public static enum ComparisonOperator {
         VC_EQ("eq"),
         VC_NE("ne"),
diff --git a/src/main/java/org/rumbledb/expressions/control/ConditionalExpression.java b/src/main/java/org/rumbledb/expressions/control/ConditionalExpression.java
index 81247b76ac..58fab4c5ac 100644
--- a/src/main/java/org/rumbledb/expressions/control/ConditionalExpression.java
+++ b/src/main/java/org/rumbledb/expressions/control/ConditionalExpression.java
@@ -33,6 +33,7 @@
 
 public class ConditionalExpression extends Expression {
 
+    private static final long serialVersionUID = 1L;
     private final Expression conditionExpression;
     private final Expression thenExpression;
     private final Expression elseExpression;
diff --git a/src/main/java/org/rumbledb/expressions/flowr/Clause.java b/src/main/java/org/rumbledb/expressions/flowr/Clause.java
index 6a35d1d897..12014636eb 100644
--- a/src/main/java/org/rumbledb/expressions/flowr/Clause.java
+++ b/src/main/java/org/rumbledb/expressions/flowr/Clause.java
@@ -34,6 +34,8 @@
 public abstract class Clause extends Node {
 
     /* Clauses are organized in doubly-linked lists */
+    private static final long serialVersionUID = 1L;
+
     protected Clause previousClause;
     protected Clause nextClause;
     protected FLWOR_CLAUSES clauseType;
diff --git a/src/main/java/org/rumbledb/expressions/flowr/CountClause.java b/src/main/java/org/rumbledb/expressions/flowr/CountClause.java
index 3392464788..3edd67d359 100644
--- a/src/main/java/org/rumbledb/expressions/flowr/CountClause.java
+++ b/src/main/java/org/rumbledb/expressions/flowr/CountClause.java
@@ -30,6 +30,7 @@
 
 
 public class CountClause extends Clause {
+    private static final long serialVersionUID = 1L;
     private VariableReferenceExpression countClauseVar;
 
     public CountClause(VariableReferenceExpression countClauseVar, ExceptionMetadata metadata) {
diff --git a/src/main/java/org/rumbledb/expressions/flowr/FlworExpression.java b/src/main/java/org/rumbledb/expressions/flowr/FlworExpression.java
index f728b0a023..73c930e8d6 100644
--- a/src/main/java/org/rumbledb/expressions/flowr/FlworExpression.java
+++ b/src/main/java/org/rumbledb/expressions/flowr/FlworExpression.java
@@ -32,6 +32,7 @@
 
 public class FlworExpression extends Expression {
 
+    private static final long serialVersionUID = 1L;
     private ReturnClause returnClause;
 
     public FlworExpression(
diff --git a/src/main/java/org/rumbledb/expressions/flowr/ForClause.java b/src/main/java/org/rumbledb/expressions/flowr/ForClause.java
index 31a3373a17..bc686114af 100644
--- a/src/main/java/org/rumbledb/expressions/flowr/ForClause.java
+++ b/src/main/java/org/rumbledb/expressions/flowr/ForClause.java
@@ -36,6 +36,7 @@
 
 public class ForClause extends Clause {
 
+    private static final long serialVersionUID = 1L;
     private final Name variableName;
     private final boolean allowingEmpty;
     private final Name positionalVariableName;
diff --git a/src/main/java/org/rumbledb/expressions/flowr/GroupByClause.java b/src/main/java/org/rumbledb/expressions/flowr/GroupByClause.java
index d4fb0ccd63..3eb1cb3ee7 100644
--- a/src/main/java/org/rumbledb/expressions/flowr/GroupByClause.java
+++ b/src/main/java/org/rumbledb/expressions/flowr/GroupByClause.java
@@ -32,6 +32,7 @@
 
 public class GroupByClause extends Clause {
 
+    private static final long serialVersionUID = 1L;
     private final List<GroupByVariableDeclaration> variables;
 
     public GroupByClause(List<GroupByVariableDeclaration> variables, ExceptionMetadata metadata) {
diff --git a/src/main/java/org/rumbledb/expressions/flowr/LetClause.java b/src/main/java/org/rumbledb/expressions/flowr/LetClause.java
index 8be7d8545d..ec8eebff98 100644
--- a/src/main/java/org/rumbledb/expressions/flowr/LetClause.java
+++ b/src/main/java/org/rumbledb/expressions/flowr/LetClause.java
@@ -36,6 +36,7 @@
 
 public class LetClause extends Clause {
 
+    private static final long serialVersionUID = 1L;
     private final Name variableName;
     protected SequenceType sequenceType;
     protected Expression expression;
diff --git a/src/main/java/org/rumbledb/expressions/flowr/OrderByClause.java b/src/main/java/org/rumbledb/expressions/flowr/OrderByClause.java
index 5d892a177f..b5bb218af1 100644
--- a/src/main/java/org/rumbledb/expressions/flowr/OrderByClause.java
+++ b/src/main/java/org/rumbledb/expressions/flowr/OrderByClause.java
@@ -31,6 +31,7 @@
 
 public class OrderByClause extends Clause {
 
+    private static final long serialVersionUID = 1L;
 
     private final List<OrderByClauseSortingKey> sortingKeys;
     private final boolean isStable;
diff --git a/src/main/java/org/rumbledb/expressions/flowr/ReturnClause.java b/src/main/java/org/rumbledb/expressions/flowr/ReturnClause.java
index 5753a05840..f03e2420b9 100644
--- a/src/main/java/org/rumbledb/expressions/flowr/ReturnClause.java
+++ b/src/main/java/org/rumbledb/expressions/flowr/ReturnClause.java
@@ -32,6 +32,7 @@
 
 public class ReturnClause extends Clause {
 
+    private static final long serialVersionUID = 1L;
 
     private final Expression returnExpr;
 
diff --git a/src/main/java/org/rumbledb/expressions/flowr/SimpleMapExpression.java b/src/main/java/org/rumbledb/expressions/flowr/SimpleMapExpression.java
index 91ef9bc425..9d5a6ffc2f 100644
--- a/src/main/java/org/rumbledb/expressions/flowr/SimpleMapExpression.java
+++ b/src/main/java/org/rumbledb/expressions/flowr/SimpleMapExpression.java
@@ -31,6 +31,7 @@
 import java.util.List;
 
 public class SimpleMapExpression extends Expression {
+    private static final long serialVersionUID = 1L;
     private Expression leftExpression;
     private Expression rightExpression;
 
diff --git a/src/main/java/org/rumbledb/expressions/logic/AndExpression.java b/src/main/java/org/rumbledb/expressions/logic/AndExpression.java
index 82e8759ea9..74999d6960 100644
--- a/src/main/java/org/rumbledb/expressions/logic/AndExpression.java
+++ b/src/main/java/org/rumbledb/expressions/logic/AndExpression.java
@@ -29,6 +29,8 @@
 import java.util.List;
 
 public class AndExpression extends Expression {
+    private static final long serialVersionUID = 1L;
+
     private Expression leftExpression;
     private Expression rightExpression;
 
diff --git a/src/main/java/org/rumbledb/expressions/logic/NotExpression.java b/src/main/java/org/rumbledb/expressions/logic/NotExpression.java
index 89a1d3a849..bea2dfe51e 100644
--- a/src/main/java/org/rumbledb/expressions/logic/NotExpression.java
+++ b/src/main/java/org/rumbledb/expressions/logic/NotExpression.java
@@ -32,6 +32,7 @@
 
 public class NotExpression extends Expression {
 
+    private static final long serialVersionUID = 1L;
     private Expression mainExpression;
 
     public NotExpression(Expression mainExpression, ExceptionMetadata metadata) {
diff --git a/src/main/java/org/rumbledb/expressions/logic/OrExpression.java b/src/main/java/org/rumbledb/expressions/logic/OrExpression.java
index 253815c7e5..28bc1340f6 100644
--- a/src/main/java/org/rumbledb/expressions/logic/OrExpression.java
+++ b/src/main/java/org/rumbledb/expressions/logic/OrExpression.java
@@ -29,6 +29,7 @@
 import java.util.List;
 
 public class OrExpression extends Expression {
+    private static final long serialVersionUID = 1L;
     private Expression leftExpression;
     private Expression rightExpression;
 
diff --git a/src/main/java/org/rumbledb/expressions/miscellaneous/RangeExpression.java b/src/main/java/org/rumbledb/expressions/miscellaneous/RangeExpression.java
index c8b0a71ee4..d22ac08070 100644
--- a/src/main/java/org/rumbledb/expressions/miscellaneous/RangeExpression.java
+++ b/src/main/java/org/rumbledb/expressions/miscellaneous/RangeExpression.java
@@ -31,6 +31,7 @@
 
 public class RangeExpression extends Expression {
 
+    private static final long serialVersionUID = 1L;
     private Expression leftExpression;
     private Expression rightExpression;
 
diff --git a/src/main/java/org/rumbledb/expressions/miscellaneous/StringConcatExpression.java b/src/main/java/org/rumbledb/expressions/miscellaneous/StringConcatExpression.java
index e9b19573c0..ae23b440e6 100644
--- a/src/main/java/org/rumbledb/expressions/miscellaneous/StringConcatExpression.java
+++ b/src/main/java/org/rumbledb/expressions/miscellaneous/StringConcatExpression.java
@@ -30,6 +30,7 @@
 import java.util.List;
 
 public class StringConcatExpression extends Expression {
+    private static final long serialVersionUID = 1L;
     private Expression leftExpression;
     private Expression rightExpression;
 
diff --git a/src/main/java/org/rumbledb/expressions/module/FunctionDeclaration.java b/src/main/java/org/rumbledb/expressions/module/FunctionDeclaration.java
index 0eace7ff8d..851ea75f9f 100644
--- a/src/main/java/org/rumbledb/expressions/module/FunctionDeclaration.java
+++ b/src/main/java/org/rumbledb/expressions/module/FunctionDeclaration.java
@@ -34,6 +34,7 @@
 
 public class FunctionDeclaration extends Node {
 
+    private static final long serialVersionUID = 1L;
     private final InlineFunctionExpression functionExpression;
 
     public FunctionDeclaration(
diff --git a/src/main/java/org/rumbledb/expressions/module/LibraryModule.java b/src/main/java/org/rumbledb/expressions/module/LibraryModule.java
index 08c4ca62e2..3c4c12bf89 100644
--- a/src/main/java/org/rumbledb/expressions/module/LibraryModule.java
+++ b/src/main/java/org/rumbledb/expressions/module/LibraryModule.java
@@ -31,6 +31,7 @@
 
 public class LibraryModule extends Module {
 
+    private static final long serialVersionUID = 1L;
     protected StaticContext staticContext;
     private String namespace;
     private final Prolog prolog;
diff --git a/src/main/java/org/rumbledb/expressions/module/MainModule.java b/src/main/java/org/rumbledb/expressions/module/MainModule.java
index 5e1904ad39..892a8aed4f 100644
--- a/src/main/java/org/rumbledb/expressions/module/MainModule.java
+++ b/src/main/java/org/rumbledb/expressions/module/MainModule.java
@@ -33,6 +33,7 @@
 
 public class MainModule extends Module {
 
+    private static final long serialVersionUID = 1L;
     protected StaticContext staticContext;
     private final Prolog prolog;
     private final Expression expression;
diff --git a/src/main/java/org/rumbledb/expressions/module/Module.java b/src/main/java/org/rumbledb/expressions/module/Module.java
index c35d1ae1a4..3213f21ebb 100644
--- a/src/main/java/org/rumbledb/expressions/module/Module.java
+++ b/src/main/java/org/rumbledb/expressions/module/Module.java
@@ -5,6 +5,8 @@
 import org.rumbledb.expressions.Node;
 
 public abstract class Module extends Node {
+    private static final long serialVersionUID = 1L;
+
     public Module(ExceptionMetadata metadata) {
         super(metadata);
     }
diff --git a/src/main/java/org/rumbledb/expressions/module/Prolog.java b/src/main/java/org/rumbledb/expressions/module/Prolog.java
index 1004b1367e..81331be346 100644
--- a/src/main/java/org/rumbledb/expressions/module/Prolog.java
+++ b/src/main/java/org/rumbledb/expressions/module/Prolog.java
@@ -31,6 +31,7 @@
 
 public class Prolog extends Node {
 
+    private static final long serialVersionUID = 1L;
     private List<Node> declarations;
     private List<LibraryModule> importedModules;
 
diff --git a/src/main/java/org/rumbledb/expressions/postfix/ArrayLookupExpression.java b/src/main/java/org/rumbledb/expressions/postfix/ArrayLookupExpression.java
index 64257cbf2d..9cf5a2e1fd 100644
--- a/src/main/java/org/rumbledb/expressions/postfix/ArrayLookupExpression.java
+++ b/src/main/java/org/rumbledb/expressions/postfix/ArrayLookupExpression.java
@@ -33,6 +33,8 @@
 
 public class ArrayLookupExpression extends Expression {
 
+    private static final long serialVersionUID = 1L;
+
     private Expression mainExpression;
     private Expression lookupExpression;
 
diff --git a/src/main/java/org/rumbledb/expressions/postfix/ArrayUnboxingExpression.java b/src/main/java/org/rumbledb/expressions/postfix/ArrayUnboxingExpression.java
index 1997befd7e..f71b499c82 100644
--- a/src/main/java/org/rumbledb/expressions/postfix/ArrayUnboxingExpression.java
+++ b/src/main/java/org/rumbledb/expressions/postfix/ArrayUnboxingExpression.java
@@ -33,6 +33,8 @@
 
 public class ArrayUnboxingExpression extends Expression {
 
+    private static final long serialVersionUID = 1L;
+
     private Expression mainExpression;
 
     public ArrayUnboxingExpression(Expression mainExpression, ExceptionMetadata metadata) {
diff --git a/src/main/java/org/rumbledb/expressions/postfix/DynamicFunctionCallExpression.java b/src/main/java/org/rumbledb/expressions/postfix/DynamicFunctionCallExpression.java
index d2aa9cf11e..a36afa3132 100644
--- a/src/main/java/org/rumbledb/expressions/postfix/DynamicFunctionCallExpression.java
+++ b/src/main/java/org/rumbledb/expressions/postfix/DynamicFunctionCallExpression.java
@@ -20,9 +20,11 @@
 
 package org.rumbledb.expressions.postfix;
 
+import org.rumbledb.compiler.VisitorConfig;
 import org.rumbledb.exceptions.ExceptionMetadata;
 import org.rumbledb.exceptions.OurBadException;
 import org.rumbledb.expressions.AbstractNodeVisitor;
+import org.rumbledb.expressions.ExecutionMode;
 import org.rumbledb.expressions.Expression;
 import org.rumbledb.expressions.Node;
 import java.util.ArrayList;
@@ -31,6 +33,7 @@
 
 public class DynamicFunctionCallExpression extends Expression {
 
+    private static final long serialVersionUID = 1L;
     private Expression mainExpression;
     private List<Expression> arguments;
 
@@ -115,4 +118,13 @@ public void serializeToJSONiq(StringBuffer sb, int indent) {
         }
         sb.append(")\n");
     }
+
+    @Override
+    public void initHighestExecutionMode(VisitorConfig visitorConfig) {
+        if (this.arguments.size() == 0) {
+            this.highestExecutionMode = ExecutionMode.LOCAL;
+            return;
+        }
+        this.highestExecutionMode = this.arguments.get(0).getHighestExecutionMode(visitorConfig);
+    }
 }
diff --git a/src/main/java/org/rumbledb/expressions/postfix/FilterExpression.java b/src/main/java/org/rumbledb/expressions/postfix/FilterExpression.java
index 0c700186d2..52b72abe36 100644
--- a/src/main/java/org/rumbledb/expressions/postfix/FilterExpression.java
+++ b/src/main/java/org/rumbledb/expressions/postfix/FilterExpression.java
@@ -37,6 +37,7 @@
 
 public class FilterExpression extends Expression {
 
+    private static final long serialVersionUID = 1L;
     private Expression mainExpression;
     private Expression predicateExpression;
 
diff --git a/src/main/java/org/rumbledb/expressions/postfix/ObjectLookupExpression.java b/src/main/java/org/rumbledb/expressions/postfix/ObjectLookupExpression.java
index 6e17c5eaec..02cc16461c 100644
--- a/src/main/java/org/rumbledb/expressions/postfix/ObjectLookupExpression.java
+++ b/src/main/java/org/rumbledb/expressions/postfix/ObjectLookupExpression.java
@@ -33,6 +33,7 @@
 
 public class ObjectLookupExpression extends Expression {
 
+    private static final long serialVersionUID = 1L;
     private Expression mainExpression;
     private Expression lookupExpression;
 
diff --git a/src/main/java/org/rumbledb/expressions/primary/ArrayConstructorExpression.java b/src/main/java/org/rumbledb/expressions/primary/ArrayConstructorExpression.java
index b6da96d490..51eb88cdf0 100644
--- a/src/main/java/org/rumbledb/expressions/primary/ArrayConstructorExpression.java
+++ b/src/main/java/org/rumbledb/expressions/primary/ArrayConstructorExpression.java
@@ -31,6 +31,8 @@
 
 public class ArrayConstructorExpression extends Expression {
 
+    private static final long serialVersionUID = 1L;
+
     private Expression expression;
 
     public ArrayConstructorExpression(Expression expression, ExceptionMetadata metadata) {
diff --git a/src/main/java/org/rumbledb/expressions/primary/BooleanLiteralExpression.java b/src/main/java/org/rumbledb/expressions/primary/BooleanLiteralExpression.java
index b276978f98..5e23d7e15f 100644
--- a/src/main/java/org/rumbledb/expressions/primary/BooleanLiteralExpression.java
+++ b/src/main/java/org/rumbledb/expressions/primary/BooleanLiteralExpression.java
@@ -31,6 +31,8 @@
 
 public class BooleanLiteralExpression extends Expression {
 
+    private static final long serialVersionUID = 1L;
+
     private boolean value;
 
     public BooleanLiteralExpression(boolean value, ExceptionMetadata metadata) {
diff --git a/src/main/java/org/rumbledb/expressions/primary/ContextItemExpression.java b/src/main/java/org/rumbledb/expressions/primary/ContextItemExpression.java
index 65e0119283..04a55e54c0 100644
--- a/src/main/java/org/rumbledb/expressions/primary/ContextItemExpression.java
+++ b/src/main/java/org/rumbledb/expressions/primary/ContextItemExpression.java
@@ -30,6 +30,8 @@
 
 public class ContextItemExpression extends Expression {
 
+    private static final long serialVersionUID = 1L;
+
     public ContextItemExpression(ExceptionMetadata metadataFromContext) {
         super(metadataFromContext);
     }
diff --git a/src/main/java/org/rumbledb/expressions/primary/DecimalLiteralExpression.java b/src/main/java/org/rumbledb/expressions/primary/DecimalLiteralExpression.java
index b1c7e35589..94ffdf141a 100644
--- a/src/main/java/org/rumbledb/expressions/primary/DecimalLiteralExpression.java
+++ b/src/main/java/org/rumbledb/expressions/primary/DecimalLiteralExpression.java
@@ -32,6 +32,7 @@
 
 public class DecimalLiteralExpression extends Expression {
 
+    private static final long serialVersionUID = 1L;
     private BigDecimal value;
 
     public DecimalLiteralExpression(BigDecimal value, ExceptionMetadata metadata) {
diff --git a/src/main/java/org/rumbledb/expressions/primary/DoubleLiteralExpression.java b/src/main/java/org/rumbledb/expressions/primary/DoubleLiteralExpression.java
index 3db15cc36a..4f0c24ec2e 100644
--- a/src/main/java/org/rumbledb/expressions/primary/DoubleLiteralExpression.java
+++ b/src/main/java/org/rumbledb/expressions/primary/DoubleLiteralExpression.java
@@ -31,6 +31,7 @@
 
 public class DoubleLiteralExpression extends Expression {
 
+    private static final long serialVersionUID = 1L;
     private double value;
 
     public DoubleLiteralExpression(double value, ExceptionMetadata metadata) {
diff --git a/src/main/java/org/rumbledb/expressions/primary/FunctionCallExpression.java b/src/main/java/org/rumbledb/expressions/primary/FunctionCallExpression.java
index ceb14792fc..e7a15e3401 100644
--- a/src/main/java/org/rumbledb/expressions/primary/FunctionCallExpression.java
+++ b/src/main/java/org/rumbledb/expressions/primary/FunctionCallExpression.java
@@ -40,6 +40,7 @@
 
 public class FunctionCallExpression extends Expression {
 
+    private static final long serialVersionUID = 1L;
     private final FunctionIdentifier identifier;
     private final List<Expression> arguments; // null for placeholder
     private final boolean isPartialApplication;
diff --git a/src/main/java/org/rumbledb/expressions/primary/InlineFunctionExpression.java b/src/main/java/org/rumbledb/expressions/primary/InlineFunctionExpression.java
index e37f19c9dc..384ae1ac5d 100644
--- a/src/main/java/org/rumbledb/expressions/primary/InlineFunctionExpression.java
+++ b/src/main/java/org/rumbledb/expressions/primary/InlineFunctionExpression.java
@@ -21,6 +21,7 @@
 package org.rumbledb.expressions.primary;
 
 
+import org.apache.commons.lang3.SerializationUtils;
 import org.rumbledb.compiler.VisitorConfig;
 import org.rumbledb.context.FunctionIdentifier;
 import org.rumbledb.context.Name;
@@ -30,21 +31,24 @@
 import org.rumbledb.expressions.Node;
 import org.rumbledb.types.SequenceType;
 
-import java.util.Arrays;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 
 public class InlineFunctionExpression extends Expression {
+    private static final long serialVersionUID = 1L;
 
     private final Name name;
     private final FunctionIdentifier functionIdentifier;
-    private final Map<Name, SequenceType> params;
+    private final LinkedHashMap<Name, SequenceType> params;
     private final SequenceType returnType;
-    private final Expression body;
+    private final Map<Long, Expression> bodies;
 
     public InlineFunctionExpression(
             Name name,
-            Map<Name, SequenceType> params,
+            LinkedHashMap<Name, SequenceType> params,
             SequenceType returnType,
             Expression body,
             ExceptionMetadata metadata
@@ -53,7 +57,12 @@ public InlineFunctionExpression(
         this.name = name;
         this.params = params;
         this.returnType = returnType;
-        this.body = body;
+        this.bodies = new HashMap<>();
+        this.bodies.put(0L, body);
+        // for inline functions, we maintain another version for ML models
+        if (this.name == null) {
+            this.bodies.put(1L, (Expression) SerializationUtils.clone(body));
+        }
         this.functionIdentifier = new FunctionIdentifier(name, params.size());
     }
 
@@ -78,12 +87,12 @@ public SequenceType getActualReturnType() {
     }
 
     public Expression getBody() {
-        return this.body;
+        return this.bodies.get(0L);
     }
 
     @Override
     public List<Node> getChildren() {
-        return Arrays.asList(this.body);
+        return new ArrayList<>(this.bodies.values());
     }
 
     public void registerUserDefinedFunctionExecutionMode(
@@ -95,7 +104,7 @@ public void registerUserDefinedFunctionExecutionMode(
             getStaticContext().getUserDefinedFunctionsExecutionModes()
                 .setExecutionMode(
                     identifier,
-                    this.body.getHighestExecutionMode(visitorConfig),
+                    this.bodies.get(0L).getHighestExecutionMode(visitorConfig),
                     visitorConfig.suppressErrorsForFunctionSignatureCollision(),
                     this.getMetadata()
                 );
@@ -124,11 +133,13 @@ public void print(StringBuffer buffer, int indent) {
         buffer.append(" | " + this.highestExecutionMode);
         buffer.append(" | " + (this.inferredSequenceType == null ? "not set" : this.inferredSequenceType));
         buffer.append("\n");
-        for (int i = 0; i < indent + 2; ++i) {
-            buffer.append("  ");
+        for (long l : this.bodies.keySet()) {
+            for (int i = 0; i < indent + 1; ++i) {
+                buffer.append("  ");
+            }
+            buffer.append("Body " + l + ":\n");
+            this.bodies.get(l).print(buffer, indent + 2);
         }
-        buffer.append("Body:\n");
-        this.body.print(buffer, indent + 2);
     }
 
     @Override
@@ -157,10 +168,14 @@ public void serializeToJSONiq(StringBuffer sb, int indent) {
                 sb.append("\n");
             indentIt(sb, indent);
             sb.append("{\n");
-            this.body.serializeToJSONiq(sb, indent + 1);
+            this.bodies.get(0L).serializeToJSONiq(sb, indent + 1);
             indentIt(sb, indent);
             sb.append("}\n");
         }
     }
+
+    public Map<Long, Expression> getBodies() {
+        return this.bodies;
+    }
 }
 
diff --git a/src/main/java/org/rumbledb/expressions/primary/IntegerLiteralExpression.java b/src/main/java/org/rumbledb/expressions/primary/IntegerLiteralExpression.java
index fcbf9a639f..1c507d88d0 100644
--- a/src/main/java/org/rumbledb/expressions/primary/IntegerLiteralExpression.java
+++ b/src/main/java/org/rumbledb/expressions/primary/IntegerLiteralExpression.java
@@ -31,6 +31,7 @@
 
 public class IntegerLiteralExpression extends Expression {
 
+    private static final long serialVersionUID = 1L;
     private String lexicalValue;
 
     public IntegerLiteralExpression(String lexicalValue, ExceptionMetadata metadata) {
diff --git a/src/main/java/org/rumbledb/expressions/primary/NamedFunctionReferenceExpression.java b/src/main/java/org/rumbledb/expressions/primary/NamedFunctionReferenceExpression.java
index b3342992c3..8dae35fb7a 100644
--- a/src/main/java/org/rumbledb/expressions/primary/NamedFunctionReferenceExpression.java
+++ b/src/main/java/org/rumbledb/expressions/primary/NamedFunctionReferenceExpression.java
@@ -32,6 +32,7 @@
 
 public class NamedFunctionReferenceExpression extends Expression {
 
+    private static final long serialVersionUID = 1L;
     private final FunctionIdentifier identifier;
 
     public NamedFunctionReferenceExpression(FunctionIdentifier identifier, ExceptionMetadata metadata) {
diff --git a/src/main/java/org/rumbledb/expressions/primary/NullLiteralExpression.java b/src/main/java/org/rumbledb/expressions/primary/NullLiteralExpression.java
index 0b7a52808e..e508119600 100644
--- a/src/main/java/org/rumbledb/expressions/primary/NullLiteralExpression.java
+++ b/src/main/java/org/rumbledb/expressions/primary/NullLiteralExpression.java
@@ -32,6 +32,8 @@
 
 public class NullLiteralExpression extends Expression {
 
+    private static final long serialVersionUID = 1L;
+
     public NullLiteralExpression(ExceptionMetadata metadata) {
         super(metadata);
     }
diff --git a/src/main/java/org/rumbledb/expressions/primary/ObjectConstructorExpression.java b/src/main/java/org/rumbledb/expressions/primary/ObjectConstructorExpression.java
index 429baf5a63..c148267d47 100644
--- a/src/main/java/org/rumbledb/expressions/primary/ObjectConstructorExpression.java
+++ b/src/main/java/org/rumbledb/expressions/primary/ObjectConstructorExpression.java
@@ -31,6 +31,7 @@
 
 public class ObjectConstructorExpression extends Expression {
 
+    private static final long serialVersionUID = 1L;
     private boolean isMergedConstructor = false;
     private List<Expression> values;
     private List<Expression> keys;
diff --git a/src/main/java/org/rumbledb/expressions/typing/CastExpression.java b/src/main/java/org/rumbledb/expressions/typing/CastExpression.java
index 6dd9e10bbe..5fea4a2e06 100644
--- a/src/main/java/org/rumbledb/expressions/typing/CastExpression.java
+++ b/src/main/java/org/rumbledb/expressions/typing/CastExpression.java
@@ -13,6 +13,8 @@
 
 public class CastExpression extends Expression {
 
+    private static final long serialVersionUID = 1L;
+
     private Expression mainExpression;
     private SequenceType sequenceType;
 
diff --git a/src/main/java/org/rumbledb/expressions/typing/CastableExpression.java b/src/main/java/org/rumbledb/expressions/typing/CastableExpression.java
index d790fa91cf..8b3fe0303c 100644
--- a/src/main/java/org/rumbledb/expressions/typing/CastableExpression.java
+++ b/src/main/java/org/rumbledb/expressions/typing/CastableExpression.java
@@ -13,6 +13,8 @@
 
 public class CastableExpression extends Expression {
 
+    private static final long serialVersionUID = 1L;
+
     protected Expression mainExpression;
     private SequenceType sequenceType;
 
diff --git a/src/main/java/org/rumbledb/expressions/typing/InstanceOfExpression.java b/src/main/java/org/rumbledb/expressions/typing/InstanceOfExpression.java
index ef730359a8..30545cc0a8 100644
--- a/src/main/java/org/rumbledb/expressions/typing/InstanceOfExpression.java
+++ b/src/main/java/org/rumbledb/expressions/typing/InstanceOfExpression.java
@@ -33,6 +33,7 @@
 
 public class InstanceOfExpression extends Expression {
 
+    private static final long serialVersionUID = 1L;
     private Expression mainExpression;
     private SequenceType sequenceType;
 
diff --git a/src/main/java/org/rumbledb/expressions/typing/IsStaticallyExpression.java b/src/main/java/org/rumbledb/expressions/typing/IsStaticallyExpression.java
index cad37ad1d1..449bcbdb03 100644
--- a/src/main/java/org/rumbledb/expressions/typing/IsStaticallyExpression.java
+++ b/src/main/java/org/rumbledb/expressions/typing/IsStaticallyExpression.java
@@ -11,6 +11,7 @@
 import java.util.List;
 
 public class IsStaticallyExpression extends Expression {
+    private static final long serialVersionUID = 1L;
     private Expression mainExpression;
     private SequenceType sequenceType;
 
diff --git a/src/main/java/org/rumbledb/items/FunctionItem.java b/src/main/java/org/rumbledb/items/FunctionItem.java
index 5a219b04c6..2d6a9cd652 100644
--- a/src/main/java/org/rumbledb/items/FunctionItem.java
+++ b/src/main/java/org/rumbledb/items/FunctionItem.java
@@ -58,7 +58,7 @@ public class FunctionItem implements Item {
 
     // signature contains type information for all parameters and the return value
     private FunctionSignature signature;
-    private RuntimeIterator bodyIterator;
+    private Map<Long, RuntimeIterator> bodyIterators;
     private DynamicContext dynamicModuleContext;
     private Map<Name, List<Item>> localVariablesInClosure;
     private Map<Name, JavaRDD<Item>> RDDVariablesInClosure;
@@ -73,12 +73,12 @@ public FunctionItem(
             List<Name> parameterNames,
             FunctionSignature signature,
             DynamicContext dynamicModuleContext,
-            RuntimeIterator bodyIterator
+            Map<Long, RuntimeIterator> bodyIterators
     ) {
         this.identifier = identifier;
         this.parameterNames = parameterNames;
         this.signature = signature;
-        this.bodyIterator = bodyIterator;
+        this.bodyIterators = bodyIterators;
         this.dynamicModuleContext = dynamicModuleContext;
         this.localVariablesInClosure = new HashMap<>();
         this.RDDVariablesInClosure = new HashMap<>();
@@ -90,7 +90,7 @@ public FunctionItem(
             List<Name> parameterNames,
             FunctionSignature signature,
             DynamicContext dynamicModuleContext,
-            RuntimeIterator bodyIterator,
+            Map<Long, RuntimeIterator> bodyIterators,
             Map<Name, List<Item>> localVariablesInClosure,
             Map<Name, JavaRDD<Item>> RDDVariablesInClosure,
             Map<Name, JSoundDataFrame> DFVariablesInClosure
@@ -98,7 +98,7 @@ public FunctionItem(
         this.identifier = identifier;
         this.parameterNames = parameterNames;
         this.signature = signature;
-        this.bodyIterator = bodyIterator;
+        this.bodyIterators = bodyIterators;
         this.dynamicModuleContext = dynamicModuleContext;
         this.localVariablesInClosure = localVariablesInClosure;
         this.RDDVariablesInClosure = RDDVariablesInClosure;
@@ -110,7 +110,7 @@ public FunctionItem(
             Map<Name, SequenceType> paramNameToSequenceTypes,
             SequenceType returnType,
             DynamicContext dynamicModuleContext,
-            RuntimeIterator bodyIterator
+            Map<Long, RuntimeIterator> bodyIterators
     ) {
         List<Name> paramNames = new ArrayList<>();
         List<SequenceType> parameters = new ArrayList<>();
@@ -122,7 +122,7 @@ public FunctionItem(
         this.identifier = new FunctionIdentifier(name, paramNames.size());
         this.parameterNames = paramNames;
         this.signature = new FunctionSignature(parameters, returnType);
-        this.bodyIterator = bodyIterator;
+        this.bodyIterators = bodyIterators;
         this.dynamicModuleContext = dynamicModuleContext;
         this.localVariablesInClosure = new HashMap<>();
         this.RDDVariablesInClosure = new HashMap<>();
@@ -149,7 +149,11 @@ public DynamicContext getModuleDynamicContext() {
     }
 
     public RuntimeIterator getBodyIterator() {
-        return this.bodyIterator;
+        return this.bodyIterators.get(0L);
+    }
+
+    public Map<Long, RuntimeIterator> getBodyIterators() {
+        return this.bodyIterators;
     }
 
     public Map<Name, List<Item>> getLocalVariablesInClosure() {
@@ -200,7 +204,9 @@ public String toString() {
             sb.append(param + " ");
         }
         sb.append("Signature: " + this.signature + "\n");
-        sb.append("Body:\n" + this.bodyIterator + "\n");
+        for (long l : this.bodyIterators.keySet()) {
+            sb.append("Body " + l + ":\n" + this.bodyIterators.get(l) + "\n");
+        }
         sb.append("Closure:\n");
         sb.append("  Local:\n");
         for (Name name : this.localVariablesInClosure.keySet()) {
@@ -243,7 +249,7 @@ public void write(Kryo kryo, Output output) {
         try {
             ByteArrayOutputStream bos = new ByteArrayOutputStream();
             ObjectOutputStream oos = new ObjectOutputStream(bos);
-            oos.writeObject(this.bodyIterator);
+            oos.writeObject(this.bodyIterators);
             oos.flush();
             byte[] data = bos.toByteArray();
             output.writeInt(data.length);
@@ -274,7 +280,7 @@ public void read(Kryo kryo, Input input) {
             byte[] data = input.readBytes(dataLength);
             ByteArrayInputStream bis = new ByteArrayInputStream(data);
             ObjectInputStream ois = new ObjectInputStream(bis);
-            this.bodyIterator = (RuntimeIterator) ois.readObject();
+            this.bodyIterators = (Map<Long, RuntimeIterator>) ois.readObject();
         } catch (Exception e) {
             throw new OurBadException(
                     "Error converting functionItem-bodyRuntimeIterator to functionItem:" + e.getMessage()
diff --git a/src/main/java/org/rumbledb/runtime/functions/DynamicFunctionCallIterator.java b/src/main/java/org/rumbledb/runtime/functions/DynamicFunctionCallIterator.java
index ec07f74a5e..4b5043e945 100644
--- a/src/main/java/org/rumbledb/runtime/functions/DynamicFunctionCallIterator.java
+++ b/src/main/java/org/rumbledb/runtime/functions/DynamicFunctionCallIterator.java
@@ -20,20 +20,23 @@
 
 package org.rumbledb.runtime.functions;
 
+import org.apache.spark.api.java.JavaRDD;
 import org.rumbledb.api.Item;
 import org.rumbledb.context.DynamicContext;
 import org.rumbledb.context.NamedFunctions;
 import org.rumbledb.exceptions.ExceptionMetadata;
 import org.rumbledb.exceptions.IteratorFlowException;
 import org.rumbledb.exceptions.MoreThanOneItemException;
+import org.rumbledb.exceptions.OurBadException;
 import org.rumbledb.exceptions.UnexpectedTypeException;
 import org.rumbledb.expressions.ExecutionMode;
-import org.rumbledb.runtime.LocalRuntimeIterator;
+import org.rumbledb.items.structured.JSoundDataFrame;
+import org.rumbledb.runtime.HybridRuntimeIterator;
 import org.rumbledb.runtime.RuntimeIterator;
 
 import java.util.List;
 
-public class DynamicFunctionCallIterator extends LocalRuntimeIterator {
+public class DynamicFunctionCallIterator extends HybridRuntimeIterator {
     // dynamic: functionIdentifier is not known at compile time
     // it is known only after evaluating postfix expression at runtime
 
@@ -67,15 +70,19 @@ public DynamicFunctionCallIterator(
     }
 
     @Override
-    public void open(DynamicContext context) {
-        super.open(context);
-        setFunctionItemAndIteratorWithCurrentContext();
+    public void openLocal() {
+        setFunctionItemAndIteratorWithCurrentContext(this.currentDynamicContextForLocalExecution);
         this.functionCallIterator.open(this.currentDynamicContextForLocalExecution);
         setNextResult();
     }
 
     @Override
-    public Item next() {
+    protected boolean hasNextLocal() {
+        return this.hasNext;
+    }
+
+    @Override
+    public Item nextLocal() {
         if (this.hasNext) {
             Item result = this.nextResult;
             setNextResult();
@@ -103,11 +110,9 @@ public void setNextResult() {
         }
     }
 
-    private void setFunctionItemAndIteratorWithCurrentContext() {
+    private void setFunctionItemAndIteratorWithCurrentContext(DynamicContext context) {
         try {
-            this.functionItem = this.functionItemIterator.materializeAtMostOneItemOrNull(
-                this.currentDynamicContextForLocalExecution
-            );
+            this.functionItem = this.functionItemIterator.materializeAtMostOneItemOrNull(context);
         } catch (MoreThanOneItemException e) {
             throw new UnexpectedTypeException(
                     "A dynamic function call can not be performed on a sequence of more than one item.",
@@ -120,6 +125,14 @@ private void setFunctionItemAndIteratorWithCurrentContext() {
                     getMetadata()
             );
         }
+        if (!this.functionItem.getBodyIterator().getHighestExecutionMode().equals(this.getHighestExecutionMode())) {
+            throw new OurBadException(
+                    "Execution mode mismatch in dynamic function call: expression expects "
+                        + this.getHighestExecutionMode()
+                        + " but function item expects "
+                        + this.functionItem.getBodyIterator().getHighestExecutionMode()
+            );
+        }
         this.functionCallIterator = NamedFunctions.buildUserDefinedFunctionCallIterator(
             this.functionItem,
             this.functionItem.getBodyIterator().getHighestExecutionMode(),
@@ -129,19 +142,29 @@ private void setFunctionItemAndIteratorWithCurrentContext() {
     }
 
     @Override
-    public void reset(DynamicContext context) {
-        super.reset(context);
+    public void resetLocal() {
         this.functionCallIterator.reset(this.currentDynamicContextForLocalExecution);
         setNextResult();
     }
 
     @Override
-    public void close() {
+    public void closeLocal() {
         // ensure that recursive function calls terminate gracefully
         // the function call in the body of the deepest recursion call is never visited, never opened and never closed
         if (this.isOpen) {
             this.functionCallIterator.close();
         }
-        super.close();
+    }
+
+    @Override
+    public JavaRDD<Item> getRDDAux(DynamicContext dynamicContext) {
+        setFunctionItemAndIteratorWithCurrentContext(dynamicContext);
+        return this.functionCallIterator.getRDD(dynamicContext);
+    }
+
+    @Override
+    public JSoundDataFrame getDataFrame(DynamicContext dynamicContext) {
+        setFunctionItemAndIteratorWithCurrentContext(dynamicContext);
+        return this.functionCallIterator.getDataFrame(dynamicContext);
     }
 }
diff --git a/src/main/java/org/rumbledb/runtime/functions/FunctionItemCallIterator.java b/src/main/java/org/rumbledb/runtime/functions/FunctionItemCallIterator.java
index 88241894dd..92d348079d 100644
--- a/src/main/java/org/rumbledb/runtime/functions/FunctionItemCallIterator.java
+++ b/src/main/java/org/rumbledb/runtime/functions/FunctionItemCallIterator.java
@@ -232,7 +232,7 @@ private RuntimeIterator generatePartiallyAppliedFunction(DynamicContext context)
                         this.functionItem.getSignature().getReturnType()
                 ),
                 this.functionItem.getModuleDynamicContext(),
-                this.functionItem.getBodyIterator(),
+                this.functionItem.getBodyIterators(),
                 localArgumentValues,
                 RDDArgumentValues,
                 DFArgumentValues
diff --git a/src/main/java/org/rumbledb/runtime/functions/FunctionRuntimeIterator.java b/src/main/java/org/rumbledb/runtime/functions/FunctionRuntimeIterator.java
index f57ad0206a..6d5c60fcdc 100644
--- a/src/main/java/org/rumbledb/runtime/functions/FunctionRuntimeIterator.java
+++ b/src/main/java/org/rumbledb/runtime/functions/FunctionRuntimeIterator.java
@@ -20,6 +20,7 @@
 
 package org.rumbledb.runtime.functions;
 
+import java.util.HashMap;
 import java.util.Map;
 
 import org.rumbledb.api.Item;
@@ -38,13 +39,13 @@ public class FunctionRuntimeIterator extends AtMostOneItemLocalRuntimeIterator {
     private Name functionName;
     private Map<Name, SequenceType> paramNameToSequenceTypes;
     SequenceType returnType;
-    RuntimeIterator bodyIterator;
+    Map<Long, RuntimeIterator> bodyIterators;
 
     public FunctionRuntimeIterator(
             Name functionName,
             Map<Name, SequenceType> paramNameToSequenceTypes,
             SequenceType returnType,
-            RuntimeIterator bodyIterator,
+            Map<Long, RuntimeIterator> bodyIterators,
             ExecutionMode executionMode,
             ExceptionMetadata iteratorMetadata
     ) {
@@ -52,18 +53,21 @@ public FunctionRuntimeIterator(
         this.functionName = functionName;
         this.paramNameToSequenceTypes = paramNameToSequenceTypes;
         this.returnType = returnType;
-        this.bodyIterator = bodyIterator;
+        this.bodyIterators = bodyIterators;
     }
 
     @Override
     public Item materializeFirstItemOrNull(DynamicContext dynamicContext) {
-        RuntimeIterator bodyIteratorCopy = ((RuntimeIterator) this.bodyIterator).deepCopy();
+        Map<Long, RuntimeIterator> bodyIteratorsCopy = new HashMap<>();
+        for (long l : this.bodyIterators.keySet()) {
+            bodyIteratorsCopy.put(l, (RuntimeIterator) this.bodyIterators.get(l).deepCopy());
+        }
         FunctionItem function = new FunctionItem(
                 this.functionName,
                 this.paramNameToSequenceTypes,
                 this.returnType,
                 dynamicContext.getModuleContext(),
-                bodyIteratorCopy
+                bodyIteratorsCopy
         );
         function.populateClosureFromDynamicContext(dynamicContext, getMetadata());
         return function;
diff --git a/src/main/java/sparksoniq/spark/ml/ApplyEstimatorRuntimeIterator.java b/src/main/java/sparksoniq/spark/ml/ApplyEstimatorRuntimeIterator.java
index 7df04db024..91b37fc8cd 100644
--- a/src/main/java/sparksoniq/spark/ml/ApplyEstimatorRuntimeIterator.java
+++ b/src/main/java/sparksoniq/spark/ml/ApplyEstimatorRuntimeIterator.java
@@ -27,7 +27,9 @@
 import java.lang.reflect.InvocationTargetException;
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import java.util.NoSuchElementException;
 
 import static sparksoniq.spark.ml.RumbleMLUtils.convertRumbleObjectItemToSparkMLParamMap;
@@ -232,11 +234,24 @@ private void setSparkMLEstimatorParamToValue(String paramName, String value) {
     }
 
     private Item generateTransformerFunctionItem(Transformer fittedModel) {
-        RuntimeIterator bodyIterator = new ApplyTransformerRuntimeIterator(
-                RumbleMLCatalog.getRumbleMLShortName(fittedModel.getClass().getName()),
-                fittedModel,
-                ExecutionMode.DATAFRAME,
-                getMetadata()
+        Map<Long, RuntimeIterator> bodyIterators = new HashMap<>();
+        bodyIterators.put(
+            0L,
+            new ApplyTransformerRuntimeIterator(
+                    RumbleMLCatalog.getRumbleMLShortName(fittedModel.getClass().getName()),
+                    fittedModel,
+                    ExecutionMode.LOCAL,
+                    getMetadata()
+            )
+        );
+        bodyIterators.put(
+            1L,
+            new ApplyTransformerRuntimeIterator(
+                    RumbleMLCatalog.getRumbleMLShortName(fittedModel.getClass().getName()),
+                    fittedModel,
+                    ExecutionMode.DATAFRAME,
+                    getMetadata()
+            )
         );
         List<SequenceType> paramTypes = Collections.unmodifiableList(
             Arrays.asList(
@@ -266,7 +281,7 @@ private Item generateTransformerFunctionItem(Transformer fittedModel) {
                         returnType
                 ),
                 new DynamicContext(this.currentDynamicContextForLocalExecution.getRumbleRuntimeConfiguration()),
-                bodyIterator
+                bodyIterators
         );
     }
 }
diff --git a/src/main/java/sparksoniq/spark/ml/GetEstimatorFunctionIterator.java b/src/main/java/sparksoniq/spark/ml/GetEstimatorFunctionIterator.java
index 011ba47834..33c25dc2aa 100644
--- a/src/main/java/sparksoniq/spark/ml/GetEstimatorFunctionIterator.java
+++ b/src/main/java/sparksoniq/spark/ml/GetEstimatorFunctionIterator.java
@@ -40,7 +40,9 @@
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class GetEstimatorFunctionIterator extends LocalFunctionCallIterator {
 
@@ -107,11 +109,24 @@ public Item next() {
             this.hasNext = false;
             try {
                 Estimator<?> estimator = (Estimator<?>) this.estimatorSparkMLClass.newInstance();
-                RuntimeIterator bodyIterator = new ApplyEstimatorRuntimeIterator(
-                        this.estimatorShortName,
-                        estimator,
-                        ExecutionMode.LOCAL,
-                        getMetadata()
+                Map<Long, RuntimeIterator> bodyIterators = new HashMap<>();
+                bodyIterators.put(
+                    0L,
+                    new ApplyEstimatorRuntimeIterator(
+                            this.estimatorShortName,
+                            estimator,
+                            ExecutionMode.LOCAL,
+                            getMetadata()
+                    )
+                );
+                bodyIterators.put(
+                    1L,
+                    new ApplyEstimatorRuntimeIterator(
+                            this.estimatorShortName,
+                            estimator,
+                            ExecutionMode.DATAFRAME,
+                            getMetadata()
+                    )
                 );
                 List<SequenceType> paramTypes = Collections.unmodifiableList(
                     Arrays.asList(
@@ -143,7 +158,7 @@ public Item next() {
                                 returnType
                         ),
                         new DynamicContext(this.currentDynamicContextForLocalExecution.getRumbleRuntimeConfiguration()),
-                        bodyIterator
+                        bodyIterators
                 );
 
             } catch (InstantiationException | IllegalAccessException e) {
diff --git a/src/main/java/sparksoniq/spark/ml/GetTransformerFunctionIterator.java b/src/main/java/sparksoniq/spark/ml/GetTransformerFunctionIterator.java
index c12ab7b965..7adb46f784 100644
--- a/src/main/java/sparksoniq/spark/ml/GetTransformerFunctionIterator.java
+++ b/src/main/java/sparksoniq/spark/ml/GetTransformerFunctionIterator.java
@@ -40,7 +40,9 @@
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class GetTransformerFunctionIterator extends LocalFunctionCallIterator {
 
@@ -107,11 +109,24 @@ public Item next() {
             this.hasNext = false;
             try {
                 Transformer transformer = (Transformer) this.transformerSparkMLClass.newInstance();
-                RuntimeIterator bodyIterator = new ApplyTransformerRuntimeIterator(
-                        this.transformerShortName,
-                        transformer,
-                        ExecutionMode.DATAFRAME,
-                        getMetadata()
+                Map<Long, RuntimeIterator> bodyIterators = new HashMap<>();
+                bodyIterators.put(
+                    0L,
+                    new ApplyTransformerRuntimeIterator(
+                            this.transformerShortName,
+                            transformer,
+                            ExecutionMode.LOCAL,
+                            getMetadata()
+                    )
+                );
+                bodyIterators.put(
+                    1L,
+                    new ApplyTransformerRuntimeIterator(
+                            this.transformerShortName,
+                            transformer,
+                            ExecutionMode.DATAFRAME,
+                            getMetadata()
+                    )
                 );
                 List<SequenceType> paramTypes = Collections.unmodifiableList(
                     Arrays.asList(
@@ -143,7 +158,7 @@ public Item next() {
                                 returnType
                         ),
                         new DynamicContext(this.currentDynamicContextForLocalExecution.getRumbleRuntimeConfiguration()),
-                        bodyIterator
+                        bodyIterators
                 );
 
             } catch (InstantiationException | IllegalAccessException e) {
diff --git a/src/test/java/iq/base/AnnotationsTestsBase.java b/src/test/java/iq/base/AnnotationsTestsBase.java
index b0447c30c5..9cdc860e15 100644
--- a/src/test/java/iq/base/AnnotationsTestsBase.java
+++ b/src/test/java/iq/base/AnnotationsTestsBase.java
@@ -20,6 +20,7 @@
 
 package iq.base;
 
+import org.apache.commons.lang.exception.ExceptionUtils;
 import org.junit.Assert;
 import org.rumbledb.api.Item;
 import org.rumbledb.api.Rumble;
@@ -175,7 +176,7 @@ protected void testAnnotations(String path, RumbleRuntimeConfiguration configura
                 checkExpectedOutput(this.currentAnnotation.getOutput(), sequence);
             } catch (RumbleException exception) {
                 String errorOutput = exception.getMessage();
-                exception.printStackTrace();
+                errorOutput += "\n" + ExceptionUtils.getStackTrace(exception);
                 Assert.fail("Program did not run when expected to.\nError output: " + errorOutput + "\n");
             }
         } else {