From 2da3720c0f3b4ceb62f6ffabc3e2bdf3b57a5b02 Mon Sep 17 00:00:00 2001
From: Roland Conybeare <rconybeare@gmail.com>
Date: Sat, 28 Feb 2026 13:20:11 +1100
Subject: [PATCH] xo-interpreter2 stack: support 0-argument function calls

---
 .../interpreter2/VirtualSchematikaMachine.cpp | 21 +++++++++++++++----
 .../include/xo/procedure2/DPrimitive.hpp      |  1 -
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/xo-interpreter2/src/interpreter2/VirtualSchematikaMachine.cpp b/xo-interpreter2/src/interpreter2/VirtualSchematikaMachine.cpp
index c258cdd6..c2221aed 100644
--- a/xo-interpreter2/src/interpreter2/VirtualSchematikaMachine.cpp
+++ b/xo-interpreter2/src/interpreter2/VirtualSchematikaMachine.cpp
@@ -699,11 +699,24 @@ namespace xo {
 
                     // now i_arg is 0 -> evaluate that argument
 
-                    this->expr_ = apply_expr->arg(i_arg);
-                    this->pc_ = VsmInstr::c_eval;
-                    this->cont_ = VsmInstr::c_evalargs;
+                    if (i_arg >= static_cast<int32_t>(apply_expr->n_args())) {
+                        // corner case: function with 0 arguments
 
-                    return;
+                        this->fn_ = apply_frame->fn(); // = value;
+                        this->args_ = apply_frame->args(); // empty
+
+                        this->stack_ = apply_frame->parent();
+                        this->pc_ = VsmInstr::c_apply;
+                        this->cont_ = apply_frame->cont();
+
+                        return;
+                    } else {
+                        this->expr_ = apply_expr->arg(i_arg);
+                        this->pc_ = VsmInstr::c_eval;
+                        this->cont_ = VsmInstr::c_evalargs;
+
+                        return;
+                    }
                 } else {
                     // error - function position must deliver something with AProcedure?
                     // or DClosure, but we'll get to that.
diff --git a/xo-procedure2/include/xo/procedure2/DPrimitive.hpp b/xo-procedure2/include/xo/procedure2/DPrimitive.hpp
index abec46cc..e458ce3a 100644
--- a/xo-procedure2/include/xo/procedure2/DPrimitive.hpp
+++ b/xo-procedure2/include/xo/procedure2/DPrimitive.hpp
@@ -110,7 +110,6 @@ namespace xo {
                 using R = typename Traits::return_type;
 
                 assert(args);
-                assert(args->size() > 0);
 
                 obj<AAllocator> mm = rcx.allocator();