xo-expression2: + LambdaExpr ++ LocalSymtab

CMakeLists.txt

@@ -150,6 +150,32 @@ xo_add_genfacetimpl(
 
 # ----------------------------------------------------------------
 
+# note: manual target; generated code committed to git
+xo_add_genfacetimpl(
+    TARGET xo-expression2-facetimpl-expression-lambdaexpr
+    FACET_PKG xo_expression2
+    FACET Expression
+    REPR LambdaExpr
+    INPUT idl/IExpression_DLambdaExpr.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-lambdaexpr
+    FACET_PKG xo_printable2
+    FACET Printable
+    REPR LambdaExpr
+    INPUT idl/IPrintable_DLambdaExpr.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-expression-ifelseexpr

idl/IExpression_DLambdaExpr.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 DLambdaExpr state",
+    using_doxygen: true,
+    repr: "DLambdaExpr",
+    doc: ["doc for IExpression+DLambdaExpr" ],
+}

idl/IPrintable_DLambdaExpr.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 DLambdaExpr",
+    using_doxygen: true,
+    repr: "DLambdaExpr",
+    doc: [ "implement APrintable for DLambdaExpr" ],
+}

include/xo/expression2/Binding.hpp

@@ -19,6 +19,7 @@ namespace xo {
             Binding(int32_t i_link, int32_t j_slot)
                 : i_link_{i_link}, j_slot_{j_slot} {}
 
+            static Binding null() { return Binding(); }
             /** global bindings are located by symbol name **/
             static Binding global() { return Binding(s_link_global, 0); }
             static Binding local(int32_t j_slot) { return Binding(0, j_slot); }

include/xo/expression2/DLambdaExpr.hpp

@@ -0,0 +1,111 @@
+/** @file DLambdaExpr.hpp
+ *
+ *  @author Roland Conybeare, Jan 2026
+ **/
+
+#pragma once
+
+#include "Expression.hpp"
+#include "TypeRef.hpp"
+#include "exprtype.hpp"
+#include "DLocalSymtab.hpp"
+#include "DString.hpp"
+#include <xo/facet/obj.hpp>
+
+namespace xo {
+    namespace scm {
+        /** @class DLambdaExpr
+         *  @brief syntax tree for a function/procedure definition
+         *
+         **/
+        class DLambdaExpr {
+        public:
+            using AAllocator = xo::mm::AAllocator;
+            using TypeDescr = xo::reflect::TypeDescr;
+            using ppindentinfo = xo::print::ppindentinfo;
+
+        public:
+
+            /** @defgroup scm-lambdaexpr-ctors **/
+            ///@{
+
+            DLambdaExpr(TypeRef typeref,
+                        const DUniqueString * name,
+                        DLocalSymtab * local_symtab,
+                        obj<AExpression> body);
+
+#ifdef NOT_YET
+            /** create instance using memory from @p mm **/
+            static obj<AExpression,DLambdaExpr> make(obj<AAllocator> mm,
+                                                     TypeRef typeref,
+                                                     const DUniqueString * name,
+                                                     DLocalSymtab * local_symtab,
+                                                     obj<AExpression> body);
+#endif
+
+            /** create instance, using memory from @p mm **/
+            static DLambdaExpr * _make(obj<AAllocator> mm,
+                                       TypeRef typeref,
+                                       const DUniqueString * name,
+                                       DLocalSymtab * local_symtab,
+                                       obj<AExpression> body);
+            ///@}
+            /** @defgroup scm-lambdaexpr-methods **/
+            ///@{
+
+            // get_free_variables()
+            // visit_preorder()
+            // visit_layer()
+            // xform_layer()
+            // attach_envs(SymbolTable*)
+
+            ///@}
+            /** @defgroup scm-lambdaexpr-expression-facet **/
+            ///@{
+
+            exprtype extype() const noexcept;
+            TypeRef typeref() const noexcept;
+            TypeDescr valuetype() const noexcept;
+            void assign_valuetype(TypeDescr td) noexcept;
+
+            ///@}
+            /** @defgroup scm-lambdaexpr-printable-facet **/
+            ///@{
+
+            bool pretty(const ppindentinfo & ppii) const;
+
+            ///@}
+
+        private:
+            /** expression value always has type consistent
+             *  with description here
+             **/
+            TypeRef typeref_;
+
+            /** name for this lambda (generated if necessary) **/
+            const DUniqueString * name_ = nullptr;
+
+#ifdef NOT_YET
+            /** e.g.
+             *    i64(f64,string)
+             *  for function of two arguments with types (f64, string) respectively,
+             *  that returns an i64.
+             **/
+            const DUniqueString * type_name_str_ = nullptr;
+#endif
+
+            /** symbol table for lambda arguments **/
+            DLocalSymtab * local_symtab_ = nullptr;;
+
+            /** expression for function body **/
+            obj<AExpression> body_expr_;
+
+            // free_var_set
+            // captured_var_set
+            // layer_var_map
+            // nested_lambda_map
+        };
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end DLambdaExpr.hpp */

include/xo/expression2/DLocalSymtab.hpp

@@ -6,6 +6,7 @@
 #pragma once
 
 #include "Binding.hpp"
+#include "DVariable.hpp"
 #include "DUniqueString.hpp"
 //#include "exprtype.hpp"
 //#include <xo/reflect/TaggedPtr.hpp>
@@ -23,15 +24,61 @@ namespace xo {
 //            using AGCObject = xo::mm::AGCObject;
 //            using typeseq = xo::reflect::typeseq;
 
+            using ppindentinfo = xo::print::ppindentinfo;
+            using AAllocator = xo::mm::AAllocator;
+            /* note: uint16_t would be fine too */
+            using size_type = std::uint32_t;
+
             struct Slot {
-                // obj<Expression,DVariable> var_;
-                Binding binding_;
+                Slot() = default;
+                explicit Slot(const DVariable * var) : var_{var} {}
+
+                /** variable representing a formal argument.
+                 *  binding will be correct only within the same layer
+                 *  as top-level lambda body
+                 *  (i.e. up to the doorstep of each and every nested lambda)
+                 **/
+                const DVariable * var_ = nullptr;
             };
 
         public:
-//            explicit DLocalSymtab(obj<AGCObject> value) noexcept;
+            /** @defgroup scm-lambdaexpr-constructors **/
+            ///@{
 
-            /** @defgroup xo-expression2-symboltable-facet symboltable facet**/
+            /** empty instance with capacity for n slots.
+             *  Caller must ensure that slots_[0..n) are actually addressable
+             **/
+            DLocalSymtab(size_type n);
+
+            /** scaffold empty symtab instance,
+             *  with capacity for @p n slots, using memory from allocator @p mm
+             **/
+            static DLocalSymtab * _make_empty(obj<AAllocator> mm, size_type n);
+
+            ///@}
+            /** @defgroup scm-lambdaexpr-methods **/
+            ///@{
+
+            size_type capacity() const noexcept { return capacity_; }
+            size_type size() const noexcept { return size_; }
+
+            const DVariable * lookup_var(Binding ix) const noexcept {
+                assert(ix.i_link() == 0);
+                assert(ix.j_slot() < static_cast<int32_t>(size_));
+
+                return slots_[ix.j_slot()].var_;
+            }
+
+            /** increase slot size (provided beleow capacity) to append
+             *  binding for one local variable.  Local variable will be allocated
+             *  from @p mm, named @p name, with type described by @p typeref.
+             **/
+            Binding append_var(obj<AAllocator> mm,
+                               const DUniqueString * name,
+                               TypeRef typeref);
+
+            ///@}
+            /** @defgroup xo-localsymtab-symboltable-facet symboltable facet**/
             ///@{
 
             /** true for global symbol table **/
@@ -41,9 +88,20 @@ namespace xo {
             Binding lookup_binding(const DUniqueString * sym) const noexcept;
 
             ///@}
+            /** @defgroup xo-localsymtab-printable-facet printable facet **/
+            ///@{
+
+            bool pretty(const ppindentinfo & ppii) const;
+
+            ///@}
 
         private:
-
+            /** actual range of slots_[] array.  Can use inices in [0,..,n) **/
+            size_type capacity_ = 0;
+            /** number of slots in use **/
+            size_type size_ = 0;
+            /** memory for names and bindings **/
+            Slot slots_[];
         };
     } /*namespace scm*/
 } /*namespace xo*/

include/xo/expression2/detail/IExpression_DLambdaExpr.hpp

@@ -0,0 +1,66 @@
+/** @file IExpression_DLambdaExpr.hpp
+ *
+ *  Generated automagically from ingredients:
+ *  1. code generator:
+ *       [/home/roland/proj/xo-umbrella2-claude1/xo-facet/codegen/genfacet]
+ *     arguments:
+ *       --input [idl/IExpression_DLambdaExpr.json5]
+ *  2. jinja2 template for abstract facet .hpp file:
+ *       [iface_facet_repr.hpp.j2]
+ *  3. idl for facet methods
+ *       [idl/IExpression_DLambdaExpr.json5]
+ **/
+
+#pragma once
+
+#include "Expression.hpp"
+#include "Expression.hpp"
+#include "DLambdaExpr.hpp"
+
+namespace xo { namespace scm { class IExpression_DLambdaExpr; } }
+
+namespace xo {
+    namespace facet {
+        template <>
+        struct FacetImplementation<xo::scm::AExpression,
+                                   xo::scm::DLambdaExpr>
+        {
+            using ImplType = xo::scm::IExpression_Xfer
+              <xo::scm::DLambdaExpr,
+               xo::scm::IExpression_DLambdaExpr>;
+        };
+    }
+}
+
+namespace xo {
+    namespace scm {
+        /** @class IExpression_DLambdaExpr
+         **/
+        class IExpression_DLambdaExpr {
+        public:
+            /** @defgroup scm-expression-dlambdaexpr-type-traits **/
+            ///@{
+            using TypeDescr = xo::scm::AExpression::TypeDescr;
+            using Copaque = xo::scm::AExpression::Copaque;
+            using Opaque = xo::scm::AExpression::Opaque;
+            ///@}
+            /** @defgroup scm-expression-dlambdaexpr-methods **/
+            ///@{
+            // const methods
+            /** expression type (constant | apply | ..) **/
+            static exprtype extype(const DLambdaExpr & self) noexcept;
+            /** placeholder for type giving possible values for this expression **/
+            static TypeRef typeref(const DLambdaExpr & self) noexcept;
+            /** type giving possible values for this expression. Maybe null before typecheck **/
+            static TypeDescr valuetype(const DLambdaExpr & self) noexcept;
+
+            // non-const methods
+            /** assing to valuetype member. Useful when scaffolding expressions **/
+            static void assign_valuetype(DLambdaExpr & self, TypeDescr td) noexcept;
+            ///@}
+        };
+
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end */

include/xo/expression2/detail/IPrintable_DLambdaExpr.hpp

@@ -0,0 +1,62 @@
+/** @file IPrintable_DLambdaExpr.hpp
+ *
+ *  Generated automagically from ingredients:
+ *  1. code generator:
+ *       [/home/roland/proj/xo-umbrella2-claude1/xo-facet/codegen/genfacet]
+ *     arguments:
+ *       --input [idl/IPrintable_DLambdaExpr.json5]
+ *  2. jinja2 template for abstract facet .hpp file:
+ *       [iface_facet_repr.hpp.j2]
+ *  3. idl for facet methods
+ *       [idl/IPrintable_DLambdaExpr.json5]
+ **/
+
+#pragma once
+
+#include "Printable.hpp"
+#include <xo/printable2/Printable.hpp>
+#include <xo/printable2/detail/IPrintable_Xfer.hpp>
+#include "DLambdaExpr.hpp"
+
+namespace xo { namespace scm { class IPrintable_DLambdaExpr; } }
+
+namespace xo {
+    namespace facet {
+        template <>
+        struct FacetImplementation<xo::print::APrintable,
+                                   xo::scm::DLambdaExpr>
+        {
+            using ImplType = xo::print::IPrintable_Xfer
+              <xo::scm::DLambdaExpr,
+               xo::scm::IPrintable_DLambdaExpr>;
+        };
+    }
+}
+
+namespace xo {
+    namespace scm {
+        /** @class IPrintable_DLambdaExpr
+         **/
+        class IPrintable_DLambdaExpr {
+        public:
+            /** @defgroup scm-printable-dlambdaexpr-type-traits **/
+            ///@{
+            using ppindentinfo = xo::print::APrintable::ppindentinfo;
+            using Copaque = xo::print::APrintable::Copaque;
+            using Opaque = xo::print::APrintable::Opaque;
+            ///@}
+            /** @defgroup scm-printable-dlambdaexpr-methods **/
+            ///@{
+            // const methods
+            /** Pretty-printing support for this object.
+See [xo-indentlog/xo/indentlog/pretty.hpp] **/
+            static bool pretty(const DLambdaExpr & self, const ppindentinfo & ppii);
+
+            // non-const methods
+            ///@}
+        };
+
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end */

include/xo/expression2/exprtype.hpp

@@ -32,10 +32,10 @@ namespace xo {
 #endif
             /** function call **/
             apply,
-#ifdef NOT_YET
+
             /** function definition **/
             lambda,
-#endif
+
             /** variable reference **/
             variable,
             /** if-then-else **/

src/expression2/CMakeLists.txt

@@ -7,6 +7,7 @@ set(SELF_SRCS
     DConstant.cpp
     DVariable.cpp
     DDefineExpr.cpp
+    DLambdaExpr.cpp
     DApplyExpr.cpp
     DIfElseExpr.cpp
 
@@ -26,6 +27,9 @@ set(SELF_SRCS
     IExpression_DApplyExpr.cpp
     IPrintable_DApplyExpr.cpp
 
+    IExpression_DLambdaExpr.cpp
+    IPrintable_DLambdaExpr.cpp
+
     IExpression_DIfElseExpr.cpp
     IPrintable_DIfElseExpr.cpp
 

src/expression2/DLambdaExpr.cpp

@@ -0,0 +1,129 @@
+/** @file DLambda.cpp
+ *
+ *  @author Roland Conybeare, Jan 2026
+ **/
+
+#include "DLambdaExpr.hpp"
+// #include "detail/IExpression_DLambdaExpr.hpp"
+#include <xo/alloc2/Allocator.hpp>
+#include <xo/printable2/Printable.hpp>
+#include <xo/facet/FacetRegistry.hpp>
+#include <xo/reflectutil/typeseq.hpp>
+
+namespace xo {
+    using xo::print::APrintable;
+    using xo::facet::FacetRegistry;
+    using xo::reflect::TypeDescr;
+    using xo::reflect::typeseq;
+
+    namespace scm {
+
+#ifdef NOT_YET
+        TypeDescr
+        assemble_lambda_td()
+        {
+            std::vector<TypeDescr> arg_td_v;
+            {
+                arg_td_v.reserve(local_symtab->size());
+
+                for (DLocalSymtab::size_type i = 0, n = local_symtab->size(); i < n; ++i) {
+                    const DVariable * var = local_symtab->lookup_var(i);
+
+                    if (!var)
+                        break;
+
+                    TypeDescr arg_td = var->valuetype();
+
+                    if (!arg_td)
+                        break;
+
+                    arg_td_v.push_back(arg_td);
+                }
+            }
+        }
+#endif
+
+        DLambdaExpr::DLambdaExpr(TypeRef typeref,
+                                 const DUniqueString * name,
+                                 DLocalSymtab * local_symtab,
+                                 obj<AExpression> body) : typeref_{typeref},
+                                                          name_{name},
+                                                          local_symtab_{local_symtab},
+                                                          body_expr_{body}
+        {
+        }
+
+#ifdef NOT_YET
+        obj<AExpression,DLambdaExpr>
+        DLambdaExpr::make(obj<AAllocator> mm,
+                          TypeRef typeref,
+                          const DUniqueString * name,
+                          DLocalSymtab * local_symtab,
+                          obj<AExpression> body)
+        {
+            return obj<AExpression,DLambdaExpr>(_make(mm, typeref,
+                                                      name, local_symtab, body);
+        }
+#endif
+
+        DLambdaExpr *
+        DLambdaExpr::_make(obj<AAllocator> mm,
+                           TypeRef typeref,
+                           const DUniqueString * name,
+                           DLocalSymtab * local_symtab,
+                           obj<AExpression> body)
+        {
+            // in general we're not going to know argument types yet.
+            // perhaps want to delay this until after type resolution.
+
+            void * mem = mm.alloc(typeseq::id<DLambdaExpr>(), sizeof(DLambdaExpr));
+
+            return new (mem) DLambdaExpr(typeref,
+                                         name,
+                                         local_symtab,
+                                         body);
+        }
+
+        exprtype
+        DLambdaExpr::extype() const noexcept {
+            return exprtype::lambda;
+        }
+
+        TypeRef
+        DLambdaExpr::typeref() const noexcept {
+            return typeref_;
+        }
+
+        TypeDescr
+        DLambdaExpr::valuetype() const noexcept {
+            return typeref_.td();
+        }
+
+        void
+        DLambdaExpr::assign_valuetype(TypeDescr td) noexcept {
+            typeref_.resolve(td);
+        }
+
+        bool
+        DLambdaExpr::pretty(const ppindentinfo & ppii) const
+        {
+            auto body
+                = FacetRegistry::instance().try_variant<APrintable,
+                                                        AExpression>(body_expr_);
+
+            if (name_ && body) {
+                return ppii.pps()->pretty_struct(ppii,
+                                                 "LambdaExpr",
+                                                 refrtag("name", name_),
+                                                 //refrtag("argv", local_env_->argv()),
+                                                 refrtag("body", body));
+            } else {
+                return ppii.pps()->pretty_struct(ppii,
+                                                 "LambdaExpr");
+            }
+        }
+
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end DLambda.cpp */

src/expression2/DLocalSymtab.cpp

@@ -8,13 +8,62 @@
 #include <xo/indentlog/scope.hpp>
 
 namespace xo {
+    using xo::facet::typeseq;
+
     namespace scm {
 
+        DLocalSymtab::DLocalSymtab(size_type n) : capacity_{n}, size_{0}
+        {
+            for (size_type i = 0; i < n; ++i) {
+                void * mem = &slots_[i];
+                new (mem) Slot();
+            }
+        }
+
+        DLocalSymtab *
+        DLocalSymtab::_make_empty(obj<AAllocator> mm, size_type n)
+        {
+            void * mem = mm.alloc(typeseq::id<DLocalSymtab>(),
+                                  sizeof(DLocalSymtab) + (n * sizeof(Slot)));
+
+            return new (mem) DLocalSymtab(n);
+        }
+
+        Binding
+        DLocalSymtab::append_var(obj<AAllocator> mm,
+                                 const DUniqueString * name,
+                                 TypeRef typeref)
+        {
+            assert(name);
+
+            if (size_ >= capacity_ || !name) {
+                assert(false);
+
+                return Binding::null();
+            } else {
+                size_type i_slot = (this->size_)++;
+                Binding binding = Binding::local(i_slot);
+                DVariable * var = DVariable::make(mm, name, typeref, binding);
+
+                this->slots_[i_slot] = Slot(var);
+
+                return binding;
+            }
+        }
+
         Binding
         DLocalSymtab::lookup_binding(const DUniqueString * sym) const noexcept
         {
-            scope log(XO_DEBUG(true), "stub impl");
-            log && log(xtag("sym", std::string_view(*sym)));
+            assert(sym);
+
+            if (sym) {
+                for (size_type i = 0; i < size_; ++i) {
+                    const Slot & slot = slots_[i];
+
+                    if (*sym == *(slot.var_->name()))
+                        return slot.var_->path();
+                }
+            }
 
             return Binding();
         }

src/expression2/IExpression_DLambdaExpr.cpp

@@ -0,0 +1,45 @@
+/** @file IExpression_DLambdaExpr.cpp
+ *
+ *  Generated automagically from ingredients:
+ *  1. code generator:
+ *       [/home/roland/proj/xo-umbrella2-claude1/xo-facet/codegen/genfacet]
+ *     arguments:
+ *       --input [idl/IExpression_DLambdaExpr.json5]
+ *  2. jinja2 template for abstract facet .hpp file:
+ *       [iface_facet_any.hpp.j2]
+ *  3. idl for facet methods
+ *       [idl/IExpression_DLambdaExpr.json5]
+**/
+
+#include "detail/IExpression_DLambdaExpr.hpp"
+
+namespace xo {
+    namespace scm {
+        auto
+        IExpression_DLambdaExpr::extype(const DLambdaExpr & self) noexcept -> exprtype
+        {
+            return self.extype();
+        }
+
+        auto
+        IExpression_DLambdaExpr::typeref(const DLambdaExpr & self) noexcept -> TypeRef
+        {
+            return self.typeref();
+        }
+
+        auto
+        IExpression_DLambdaExpr::valuetype(const DLambdaExpr & self) noexcept -> TypeDescr
+        {
+            return self.valuetype();
+        }
+
+        auto
+        IExpression_DLambdaExpr::assign_valuetype(DLambdaExpr & self, TypeDescr td) noexcept -> void
+        {
+            self.assign_valuetype(td);
+        }
+
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end IExpression_DLambdaExpr.cpp */

src/expression2/IPrintable_DLambdaExpr.cpp

@@ -0,0 +1,28 @@
+/** @file IPrintable_DLambdaExpr.cpp
+ *
+ *  Generated automagically from ingredients:
+ *  1. code generator:
+ *       [/home/roland/proj/xo-umbrella2-claude1/xo-facet/codegen/genfacet]
+ *     arguments:
+ *       --input [idl/IPrintable_DLambdaExpr.json5]
+ *  2. jinja2 template for abstract facet .hpp file:
+ *       [iface_facet_any.hpp.j2]
+ *  3. idl for facet methods
+ *       [idl/IPrintable_DLambdaExpr.json5]
+**/
+
+#include "detail/IPrintable_DLambdaExpr.hpp"
+
+namespace xo {
+    namespace scm {
+        auto
+        IPrintable_DLambdaExpr::pretty(const DLambdaExpr & self, const ppindentinfo & ppii) -> bool
+        {
+            return self.pretty(ppii);
+        }
+
+
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end IPrintable_DLambdaExpr.cpp */

src/expression2/expression2_register_facets.cpp

@@ -20,6 +20,9 @@
 #include <xo/expression2/detail/IExpression_DApplyExpr.hpp>
 #include <xo/expression2/detail/IPrintable_DApplyExpr.hpp>
 
+#include <xo/expression2/detail/IExpression_DLambdaExpr.hpp>
+#include <xo/expression2/detail/IPrintable_DLambdaExpr.hpp>
+
 #include <xo/expression2/detail/IExpression_DIfElseExpr.hpp>
 #include <xo/expression2/detail/IPrintable_DIfElseExpr.hpp>
 
@@ -48,6 +51,7 @@ namespace xo {
             // +- Variable
             // +- DefineExpr
             // +- ApplyExpr
+            // +- LambdaExpr
             // \- IfElseExpr
 
             FacetRegistry::register_impl<AExpression, DConstant>();
@@ -62,6 +66,9 @@ namespace xo {
             FacetRegistry::register_impl<AExpression, DApplyExpr>();
             FacetRegistry::register_impl<APrintable, DApplyExpr>();
 
+            FacetRegistry::register_impl<AExpression, DLambdaExpr>();
+            FacetRegistry::register_impl<APrintable, DLambdaExpr>();
+
             FacetRegistry::register_impl<AExpression, DIfElseExpr>();
             FacetRegistry::register_impl<APrintable, DIfElseExpr>();
 
@@ -70,6 +77,7 @@ namespace xo {
             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("DLambdaExpr.tseq", typeseq::id<DLambdaExpr>()));
             log && log(xtag("DIfElseExpr.tseq", typeseq::id<DIfElseExpr>()));
 
             log && log(xtag("AExpression.tqseq", typeseq::id<AExpression>()));