Allow a sequence of function items in dynamic function calls

basex-core/src/main/java/org/basex/query/QueryParser.java

@@ -2506,7 +2506,7 @@ private Expr postfix() throws QueryException {
         } else if(consume("=?>")) {
           expr = methodCall(expr);
         } else if(current('(')) {
-          expr = Functions.dynamic(expr, argumentList(false, null));
+          expr = dynamicFunctionCall(expr);
         } else if(current('?')) {
           expr = lookup(expr);
           if(expr == null) break;
@@ -2557,6 +2557,25 @@ private Expr methodCall(final Expr expr) throws QueryException {
     return gflwor;
   }
 
+  /**
+   * Parses the "DynamicFunctionCall" rule.
+   * @param expr expression
+   * @return query expression
+   * @throws QueryException query exception
+   */
+  private Expr dynamicFunctionCall(final Expr expr) throws QueryException {
+    final InputInfo info = info();
+    final FuncBuilder fb = argumentList(false, null);
+    if(expr.seqType().one()) return Functions.dynamic(expr, fb);
+    final int s = localVars.openScope();
+    final For fr = new For(localVars.add(new Var(new QNm("fn"), null, qc, info)), expr);
+    final VarRef func = new VarRef(info, fr.var);
+    final Expr call = Functions.dynamic(func, fb);
+    final GFLWOR gflwor = new GFLWOR(info, fr, call);
+    localVars.closeScope(s);
+    return gflwor;
+  }
+
   /**
    * Parses the "PrimaryExpr" rule.
    * Parses the "VarRef" rule.

basex-core/src/main/java/org/basex/query/func/DynFuncCall.java

@@ -72,7 +72,14 @@ public Expr optimize(final CompileContext cc) throws QueryException {
     if(ft != null) {
       if(ft.argTypes != null) {
         final int arity = ft.argTypes.length;
-        if(nargs != arity) throw arityError(func, nargs, arity, false, info);
+        if(nargs != arity) {
+          Expr funcItem = func;
+          if(func instanceof VarRef ref) {
+            final Expr expr = ref.var.expr();
+            if(expr instanceof FuncItem) funcItem = expr;
+          }
+          throw arityError(funcItem, nargs, arity, false, info);
+        }
       }
       if(!sc().mixUpdates && !updating && ft.anns.contains(Annotation.UPDATING)) {
         throw FUNCUP_X.get(info, func);

basex-core/src/main/java/org/basex/query/var/Var.java

@@ -93,6 +93,14 @@ public void expr(final Expr expr) {
     ex = expr;
   }
 
+  /**
+   * Returns the input expression.
+   * @return input expression (can be {@code null} if not yet set)
+   */
+  public Expr expr() {
+    return ex;
+  }
+
   /**
    * Returns the result size.
    * @return result size

basex-core/src/test/java/org/basex/query/expr/HigherOrderTest.java

@@ -107,7 +107,8 @@ public final class HigherOrderTest extends SandboxTest {
 
   /**  Test for invalid function expressions. */
   @Test public void invalidFunTest() {
-    error("()()", INVFUNCITEM_X_X);
+    query("()()", "");
+
     error("1()", INVFUNCITEM_X_X);
     error("1.0()", INVFUNCITEM_X_X);
     error("1e0()", INVFUNCITEM_X_X);

basex-core/src/test/java/org/basex/query/simple/SimpleTest.java

@@ -125,8 +125,8 @@ public final class SimpleTest extends QueryTest {
       { "Seq 3", integers(1, 2), "((( 1, 2 )  )    )" },
       { "Seq 4", integers(1, 2, 3), "(1, (( 2,3 )  )    )" },
       { "Seq 5", integers(1, 2, 3, 4), "(1, (( 2,3 )  ),4   )" },
-      { "Seq 6", "()()" },
-      { "Seq 7", "() ()" },
+      { "Seq 6", emptySequence(), "()()" },
+      { "Seq 7", emptySequence(), "() ()" },
 
       { "IntersectExcept 1", emptySequence(), "<a/> intersect <b/>" },
       { "IntersectExcept 2", emptySequence(), "<a/> intersect <b/> except <c/>" },