diff --git a/CMakeLists.txt b/CMakeLists.txt
index 52e9d380..869f891d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -124,6 +124,32 @@ xo_add_genfacetimpl(
 
 # ----------------------------------------------------------------
 
+# note: manual target; generated code committed to git
+xo_add_genfacetimpl(
+    TARGET xo-expression2-facetimpl-expression-applyexpr
+    FACET_PKG xo_expression2
+    FACET Expression
+    REPR ApplyExpr
+    INPUT idl/IExpression_DApplyExpr.json5
+    OUTPUT_HPP_DIR include/xo/expression2
+    OUTPUT_IMPL_SUBDIR detail
+    OUTPUT_CPP_DIR src/expression2
+)
+
+# note: manual target; generated code committed to git
+xo_add_genfacetimpl(
+    TARGET xo-expression2-facetimpl-printable-applyexpr
+    FACET_PKG xo_printable2
+    FACET Printable
+    REPR ApplyExpr
+    INPUT idl/IPrintable_DApplyExpr.json5
+    OUTPUT_HPP_DIR include/xo/expression2
+    OUTPUT_IMPL_SUBDIR detail
+    OUTPUT_CPP_DIR src/expression2
+)
+
+# ----------------------------------------------------------------
+
 # note: manual target; generated code committed to git
 xo_add_genfacetimpl(
     TARGET xo-expression2-facetimpl-gcobject-uniquestring
diff --git a/idl/IExpression_DApplyExpr.json5 b/idl/IExpression_DApplyExpr.json5
new file mode 100644
index 00000000..6814547c
--- /dev/null
+++ b/idl/IExpression_DApplyExpr.json5
@@ -0,0 +1,12 @@
+{
+    mode: "implementation",
+    includes: [ "\"Expression.hpp\"" ],
+    local_types: [ ],
+    namespace1: "xo",
+    namespace2: "scm",
+    facet_idl: "idl/Expression.json5",
+    brief: "provide AExpression interface for DApplyExpr state",
+    using_doxygen: true,
+    repr: "DApplyExpr",
+    doc: ["doc for IExpression+DApplyExpr" ],
+}
diff --git a/idl/IPrintable_DApplyExpr.json5 b/idl/IPrintable_DApplyExpr.json5
new file mode 100644
index 00000000..fe743b0b
--- /dev/null
+++ b/idl/IPrintable_DApplyExpr.json5
@@ -0,0 +1,13 @@
+{
+    mode: "implementation",
+    includes: [ "<xo/printable2/Printable.hpp>",
+                "<xo/printable2/detail/IPrintable_Xfer.hpp>" ],
+    local_types: [ ],
+    namespace1: "xo",
+    namespace2: "scm",
+    facet_idl: "idl/Printable.json5",
+    brief: "provide APrintable interface for DApplyExpr",
+    using_doxygen: true,
+    repr: "DApplyExpr",
+    doc: [ "implement APrintable for DApplyExpr" ],
+}
diff --git a/include/xo/expression2/DApplyExpr.hpp b/include/xo/expression2/DApplyExpr.hpp
index 882cf5cd..8502c62a 100644
--- a/include/xo/expression2/DApplyExpr.hpp
+++ b/include/xo/expression2/DApplyExpr.hpp
@@ -20,18 +20,55 @@ namespace xo {
          **/
         class DApplyExpr {
         public:
+            using AAllocator = xo::mm::AAllocator;
             using TypeDescr = xo::reflect::TypeDescr;
             using ppindentinfo = xo::print::ppindentinfo;
-            using size_type = std::size_t;
+            using size_type = std::uint32_t;
 
         public:
+            /** @defgroup scm-applyexpr-constructors **/
+            ///@{
+
+            /** construct empty instance, but with argument expressions empty **/
+            DApplyExpr(TypeRef typeref,
+                       obj<AExpression> fn_expr,
+                       size_type n_args);
+
+            /** create apply for function with 2 arguments **/
+            static obj<AExpression,DApplyExpr> make2(obj<AAllocator> mm,
+                                                     TypeRef typeref,
+                                                     obj<AExpression> fn_expr,
+                                                     obj<AExpression> arg1,
+                                                     obj<AExpression> arg2);
+
+            /** create apply for function with 2 arguments **/
+            static DApplyExpr * _make2(obj<AAllocator> mm,
+                                       TypeRef typeref,
+                                       obj<AExpression> fn_expr,
+                                       obj<AExpression> arg1,
+                                       obj<AExpression> arg2);
+
+            /** scaffold incomplete instance.
+             *  apply-expr using memory from @p mm.
+             *  will construct instance with space for @p n_args arguments
+             *  but expressions left empty.
+             *  use @ref assign_arg for all arguments to complete.
+             **/
+            static DApplyExpr * scaffold(obj<AAllocator> mm,
+                                         TypeRef typeref,
+                                         obj<AExpression> fn_expr,
+                                         size_type n_args);
+            void assign_arg(size_type i_arg, obj<AExpression> expr);
+
+            ///@}
+            /** @defgroup scm-applyexpr-access-methods **/
+            ///@{
 
             obj<AExpression>  fn() const noexcept { return fn_; }
-            const DArray * args() const noexcept { return args_; }
-
-            size_type n_arg() const noexcept { return args_->size(); }
+            size_type n_args() const noexcept { return n_args_; }
             obj<AExpression> arg(size_type i) const;
 
+            ///@}
             /** @defgroup scm-applyexpr-expression-facet **/
             ///@{
 
@@ -40,6 +77,12 @@ namespace xo {
             TypeDescr valuetype() const noexcept { return typeref_.td(); }
             void assign_valuetype(TypeDescr td) noexcept;
 
+            ///@}
+            /** @defgroup scm-applyexpr-gcobject-facet **/
+            ///@{
+
+            // shallow_copy() etc.
+
             ///@}
             /** @defgroup scm-applyexpr-printable-facet **/
             ///@{
@@ -55,8 +98,10 @@ namespace xo {
             TypeRef typeref_;
             /** expression for function/procedure to invoke **/
             obj<AExpression> fn_;
-            /** expression for each argument vector **/
-            const DArray * args_;
+            /** number of arguments (not counting @ref fn_ **/
+            size_type n_args_ = 0;
+            /** args_[i] is expression for i'th argument to @ref fn_ **/
+            obj<AExpression> args_[];
         };
     }
 }
diff --git a/include/xo/expression2/detail/IExpression_DApplyExpr.hpp b/include/xo/expression2/detail/IExpression_DApplyExpr.hpp
new file mode 100644
index 00000000..c8952199
--- /dev/null
+++ b/include/xo/expression2/detail/IExpression_DApplyExpr.hpp
@@ -0,0 +1,66 @@
+/** @file IExpression_DApplyExpr.hpp
+ *
+ *  Generated automagically from ingredients:
+ *  1. code generator:
+ *       [/home/roland/proj/xo-umbrella2-claude1/xo-facet/codegen/genfacet]
+ *     arguments:
+ *       --input [idl/IExpression_DApplyExpr.json5]
+ *  2. jinja2 template for abstract facet .hpp file:
+ *       [iface_facet_repr.hpp.j2]
+ *  3. idl for facet methods
+ *       [idl/IExpression_DApplyExpr.json5]
+ **/
+
+#pragma once
+
+#include "Expression.hpp"
+#include "Expression.hpp"
+#include "DApplyExpr.hpp"
+
+namespace xo { namespace scm { class IExpression_DApplyExpr; } }
+
+namespace xo {
+    namespace facet {
+        template <>
+        struct FacetImplementation<xo::scm::AExpression,
+                                   xo::scm::DApplyExpr>
+        {
+            using ImplType = xo::scm::IExpression_Xfer
+              <xo::scm::DApplyExpr,
+               xo::scm::IExpression_DApplyExpr>;
+        };
+    }
+}
+
+namespace xo {
+    namespace scm {
+        /** @class IExpression_DApplyExpr
+         **/
+        class IExpression_DApplyExpr {
+        public:
+            /** @defgroup scm-expression-dapplyexpr-type-traits **/
+            ///@{
+            using TypeDescr = xo::scm::AExpression::TypeDescr;
+            using Copaque = xo::scm::AExpression::Copaque;
+            using Opaque = xo::scm::AExpression::Opaque;
+            ///@}
+            /** @defgroup scm-expression-dapplyexpr-methods **/
+            ///@{
+            // const methods
+            /** expression type (constant | apply | ..) **/
+            static exprtype extype(const DApplyExpr & self) noexcept;
+            /** placeholder for type giving possible values for this expression **/
+            static TypeRef typeref(const DApplyExpr & self) noexcept;
+            /** type giving possible values for this expression. Maybe null before typecheck **/
+            static TypeDescr valuetype(const DApplyExpr & self) noexcept;
+
+            // non-const methods
+            /** assing to valuetype member. Useful when scaffolding expressions **/
+            static void assign_valuetype(DApplyExpr & self, TypeDescr td) noexcept;
+            ///@}
+        };
+
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end */
\ No newline at end of file
diff --git a/include/xo/expression2/detail/IPrintable_DApplyExpr.hpp b/include/xo/expression2/detail/IPrintable_DApplyExpr.hpp
new file mode 100644
index 00000000..c05e87e2
--- /dev/null
+++ b/include/xo/expression2/detail/IPrintable_DApplyExpr.hpp
@@ -0,0 +1,62 @@
+/** @file IPrintable_DApplyExpr.hpp
+ *
+ *  Generated automagically from ingredients:
+ *  1. code generator:
+ *       [/home/roland/proj/xo-umbrella2-claude1/xo-facet/codegen/genfacet]
+ *     arguments:
+ *       --input [idl/IPrintable_DApplyExpr.json5]
+ *  2. jinja2 template for abstract facet .hpp file:
+ *       [iface_facet_repr.hpp.j2]
+ *  3. idl for facet methods
+ *       [idl/IPrintable_DApplyExpr.json5]
+ **/
+
+#pragma once
+
+#include "Printable.hpp"
+#include <xo/printable2/Printable.hpp>
+#include <xo/printable2/detail/IPrintable_Xfer.hpp>
+#include "DApplyExpr.hpp"
+
+namespace xo { namespace scm { class IPrintable_DApplyExpr; } }
+
+namespace xo {
+    namespace facet {
+        template <>
+        struct FacetImplementation<xo::print::APrintable,
+                                   xo::scm::DApplyExpr>
+        {
+            using ImplType = xo::print::IPrintable_Xfer
+              <xo::scm::DApplyExpr,
+               xo::scm::IPrintable_DApplyExpr>;
+        };
+    }
+}
+
+namespace xo {
+    namespace scm {
+        /** @class IPrintable_DApplyExpr
+         **/
+        class IPrintable_DApplyExpr {
+        public:
+            /** @defgroup scm-printable-dapplyexpr-type-traits **/
+            ///@{
+            using ppindentinfo = xo::print::APrintable::ppindentinfo;
+            using Copaque = xo::print::APrintable::Copaque;
+            using Opaque = xo::print::APrintable::Opaque;
+            ///@}
+            /** @defgroup scm-printable-dapplyexpr-methods **/
+            ///@{
+            // const methods
+            /** Pretty-printing support for this object.
+See [xo-indentlog/xo/indentlog/pretty.hpp] **/
+            static bool pretty(const DApplyExpr & self, const ppindentinfo & ppii);
+
+            // non-const methods
+            ///@}
+        };
+
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end */
\ No newline at end of file
diff --git a/src/expression2/CMakeLists.txt b/src/expression2/CMakeLists.txt
index 9dea6457..b8be9468 100644
--- a/src/expression2/CMakeLists.txt
+++ b/src/expression2/CMakeLists.txt
@@ -22,6 +22,9 @@ set(SELF_SRCS
     IExpression_DDefineExpr.cpp
     IPrintable_DDefineExpr.cpp
 
+    IExpression_DApplyExpr.cpp
+    IPrintable_DApplyExpr.cpp
+
     DLocalSymtab.cpp
     DGlobalSymtab.cpp
 
diff --git a/src/expression2/DApplyExpr.cpp b/src/expression2/DApplyExpr.cpp
index 0c0546f3..ce5e1951 100644
--- a/src/expression2/DApplyExpr.cpp
+++ b/src/expression2/DApplyExpr.cpp
@@ -11,30 +11,62 @@
 namespace xo {
     using xo::print::APrintable;
     using xo::facet::FacetRegistry;
+    using xo::reflect::typeseq;
     using xo::mm::AGCObject;
 
     namespace scm {
+        /* incomplete! */
+        DApplyExpr::DApplyExpr(TypeRef typeref,
+                               obj<AExpression> fn_expr,
+                               size_type n_args) : typeref_{typeref},
+                                                   fn_{fn_expr},
+                                                   n_args_{n_args}
+        {}
+
+        DApplyExpr *
+        DApplyExpr::scaffold(obj<AAllocator> mm,
+                             TypeRef typeref,
+                             obj<AExpression> fn_expr,
+                             size_type n_args)
+        {
+            void * mem = mm.alloc(typeseq::id<DApplyExpr>(),
+                                  sizeof(DApplyExpr) + (n_args * sizeof(obj<AExpression>)));
+
+            DApplyExpr * result = new (mem) DApplyExpr(typeref,
+                                                       fn_expr,
+                                                       n_args);
+
+            return result;
+        }
+
+        void
+        DApplyExpr::assign_arg(size_type i_arg,
+                               obj<AExpression> expr)
+        {
+            if (i_arg < n_args_) {
+                this->args_[i_arg] = expr;
+            } else {
+                assert(false);
+
+                throw std::runtime_error(tostr("assign out-of-range argument i_arg where [0..n_args) expected",
+                                               xtag("i_arg", i_arg),
+                                               xtag("expr", expr),
+                                               xtag("n_args", n_args_)));
+
+            }
+        }
+
         obj<AExpression>
         DApplyExpr::arg(size_type i) const
         {
-            if (i >= args_->size()) [[unlikely]] {
+            if (i >= n_args_) [[unlikely]] {
                 throw std::runtime_error(tostr("attempt to fetch argument i where [0..n) expected",
                                                xtag("i", i),
-                                               xtag("n", args_->size()),
+                                               xtag("n", n_args_),
                                                xtag("src", "DApplyExpr::arg")));
             }
 
-            obj<AGCObject> arg_i = args_->at(i);
-
-            auto expr_i = FacetRegistry::instance().variant<AExpression>(arg_i);
-
-            if (!expr_i) [[unlikely]] {
-                throw std::runtime_error(tostr("expected expression interface on argument i",
-                                               xtag("i", i),
-                                               xtag("arg[i]", arg_i)));
-            }
-
-            return expr_i;
+            return args_[i];
         }
 
         void
@@ -60,9 +92,9 @@ namespace xo {
                         return false;
                 }
 
-                for (size_t i_arg = 0, n_arg = this->n_arg(); i_arg < n_arg; ++i_arg) {
+                for (size_t i_arg = 0; i_arg < n_args_; ++i_arg) {
                     obj<APrintable> arg_i
-                        = FacetRegistry::instance().variant<APrintable>(this->arg(i_arg));
+                        = FacetRegistry::instance().variant<APrintable>(args_[i_arg]);
 
                     if (!pps->print_upto(refrtag(concat("arg", 1+i_arg), arg_i)))
                         return false;
@@ -78,13 +110,14 @@ namespace xo {
                 pps->newline_indent(ppii.ci1());
                 pps->pretty(refrtag("fn", fn));
 
-                for (size_t i_arg = 0, n_arg = this->n_arg(); i_arg < n_arg; ++i_arg) {
+                for (size_t i_arg = 0; i_arg < n_args_; ++i_arg) {
                     obj<APrintable> arg_i
-                        = FacetRegistry::instance().variant<APrintable>(fn_);
+                        = FacetRegistry::instance().variant<APrintable>(args_[i_arg]);
 
                     pps->newline_indent(ppii.ci1());
                     pps->pretty(refrtag(concat("arg", 1+i_arg), arg_i));
                 }
+
                 return false;
             }
         }
diff --git a/src/expression2/IExpression_DApplyExpr.cpp b/src/expression2/IExpression_DApplyExpr.cpp
new file mode 100644
index 00000000..2098e050
--- /dev/null
+++ b/src/expression2/IExpression_DApplyExpr.cpp
@@ -0,0 +1,45 @@
+/** @file IExpression_DApplyExpr.cpp
+ *
+ *  Generated automagically from ingredients:
+ *  1. code generator:
+ *       [/home/roland/proj/xo-umbrella2-claude1/xo-facet/codegen/genfacet]
+ *     arguments:
+ *       --input [idl/IExpression_DApplyExpr.json5]
+ *  2. jinja2 template for abstract facet .hpp file:
+ *       [iface_facet_any.hpp.j2]
+ *  3. idl for facet methods
+ *       [idl/IExpression_DApplyExpr.json5]
+**/
+
+#include "detail/IExpression_DApplyExpr.hpp"
+
+namespace xo {
+    namespace scm {
+        auto
+        IExpression_DApplyExpr::extype(const DApplyExpr & self) noexcept -> exprtype
+        {
+            return self.extype();
+        }
+
+        auto
+        IExpression_DApplyExpr::typeref(const DApplyExpr & self) noexcept -> TypeRef
+        {
+            return self.typeref();
+        }
+
+        auto
+        IExpression_DApplyExpr::valuetype(const DApplyExpr & self) noexcept -> TypeDescr
+        {
+            return self.valuetype();
+        }
+
+        auto
+        IExpression_DApplyExpr::assign_valuetype(DApplyExpr & self, TypeDescr td) noexcept -> void
+        {
+            self.assign_valuetype(td);
+        }
+
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end IExpression_DApplyExpr.cpp */
\ No newline at end of file
diff --git a/src/expression2/IPrintable_DApplyExpr.cpp b/src/expression2/IPrintable_DApplyExpr.cpp
new file mode 100644
index 00000000..4f4a50d3
--- /dev/null
+++ b/src/expression2/IPrintable_DApplyExpr.cpp
@@ -0,0 +1,28 @@
+/** @file IPrintable_DApplyExpr.cpp
+ *
+ *  Generated automagically from ingredients:
+ *  1. code generator:
+ *       [/home/roland/proj/xo-umbrella2-claude1/xo-facet/codegen/genfacet]
+ *     arguments:
+ *       --input [idl/IPrintable_DApplyExpr.json5]
+ *  2. jinja2 template for abstract facet .hpp file:
+ *       [iface_facet_any.hpp.j2]
+ *  3. idl for facet methods
+ *       [idl/IPrintable_DApplyExpr.json5]
+**/
+
+#include "detail/IPrintable_DApplyExpr.hpp"
+
+namespace xo {
+    namespace scm {
+        auto
+        IPrintable_DApplyExpr::pretty(const DApplyExpr & self, const ppindentinfo & ppii) -> bool
+        {
+            return self.pretty(ppii);
+        }
+
+
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end IPrintable_DApplyExpr.cpp */
\ No newline at end of file
diff --git a/src/expression2/expression2_register_facets.cpp b/src/expression2/expression2_register_facets.cpp
index 1854f3eb..fc6ef3c1 100644
--- a/src/expression2/expression2_register_facets.cpp
+++ b/src/expression2/expression2_register_facets.cpp
@@ -17,6 +17,9 @@
 #include <xo/expression2/detail/IExpression_DConstant.hpp>
 #include <xo/expression2/detail/IPrintable_DConstant.hpp>
 
+#include <xo/expression2/detail/IExpression_DApplyExpr.hpp>
+#include <xo/expression2/detail/IPrintable_DApplyExpr.hpp>
+
 #include <xo/gc/detail/AGCObject.hpp>
 #include <xo/printable2/detail/APrintable.hpp>
 #include <xo/facet/FacetRegistry.hpp>
@@ -40,7 +43,8 @@ namespace xo {
             // Expression
             // +- Constant
             // +- Variable
-            // \- DefineExpr
+            // +- DefineExpr
+            // \- ApplyExpr
 
             FacetRegistry::register_impl<AExpression, DConstant>();
             FacetRegistry::register_impl<APrintable, DConstant>();
@@ -51,10 +55,14 @@ namespace xo {
             FacetRegistry::register_impl<AExpression, DDefineExpr>();
             FacetRegistry::register_impl<APrintable, DDefineExpr>();
 
+            FacetRegistry::register_impl<AExpression, DApplyExpr>();
+            FacetRegistry::register_impl<APrintable, DApplyExpr>();
+
             log && log(xtag("DUniqueString.tseq", typeseq::id<DUniqueString>()));
             log && log(xtag("DDefineExpr.tseq", typeseq::id<DDefineExpr>()));
             log && log(xtag("DVariable.tseq", typeseq::id<DVariable>()));
             log && log(xtag("DConstant.tseq", typeseq::id<DConstant>()));
+            log && log(xtag("DApplyExpr.tseq", typeseq::id<DApplyExpr>()));
 
             log && log(xtag("AExpression.tqseq", typeseq::id<AExpression>()));