From 10d5eca372ed85d9beab8f91e0cadcd6f8e24fac Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Sun, 5 Apr 2026 21:37:17 +0100
Subject: Support null data pointer

---
 patio-to-cranelift/src/lib.rs                       |  6 ++++--
 .../shedlang/compiler/patio/PatioExampleTests.java  | 21 +++++++++++++++++++++
 .../shedlang/compiler/patio/instructions/Patio.java |  4 ++++
 3 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/patio-to-cranelift/src/lib.rs b/patio-to-cranelift/src/lib.rs
index 74dd4993..85e11f7b 100644
--- a/patio-to-cranelift/src/lib.rs
+++ b/patio-to-cranelift/src/lib.rs
@@ -568,16 +568,18 @@ fn compile_data_ptr_value(
     data_ptr_value: &PatioDataPtrValue,
     context: &mut CompilerFunctionContext<'_>,
 ) -> cranelift_codegen::ir::Value {
+    let data_ptr_type = context.pointer_type();
+
     match data_ptr_value {
         PatioDataPtrValue::DataElement { name } => {
             let global_value = context.data_ptr(name);
-            let data_ptr_type = context.pointer_type();
             context
                 .function_builder
                 .ins()
                 .global_value(data_ptr_type, global_value)
         }
-        PatioDataPtrValue::Null => todo!(),
+
+        PatioDataPtrValue::Null => context.function_builder.ins().iconst(data_ptr_type, 0),
     }
 }
 
diff --git a/src/test/java/org/shedlang/compiler/patio/PatioExampleTests.java b/src/test/java/org/shedlang/compiler/patio/PatioExampleTests.java
index 9ea6aef2..0cc1574d 100644
--- a/src/test/java/org/shedlang/compiler/patio/PatioExampleTests.java
+++ b/src/test/java/org/shedlang/compiler/patio/PatioExampleTests.java
@@ -142,6 +142,27 @@ public abstract class PatioExampleTests {
         ));
     }
 
+    @Test
+    public void dataPtrCanBeNull() throws IOException, InterruptedException {
+        var patioFunction = PatioFunctionDefinition.builder()
+            .withName(FUNCTION_NAME)
+            .addLocal(PatioLocal.val("x", PatioTypes.DATA_PTR))
+            .addBodyInstruction(Patio.localStore(
+                Patio.localRef("x"),
+                Patio.dataPtrConst(Patio.dataPtrValueNull())
+            ))
+            .withReturnType(PatioTypes.VOID)
+            .addBodyInstruction(Patio.returnVoid())
+            .build();
+        var patio = Patio.compilationUnit(List.of(
+            patioFunction
+        ));
+
+        var result = run(patio);
+
+        assertThat(result, isSequence());
+    }
+
     @Test
     public void blockSingleResult() throws IOException, InterruptedException {
         var patioFunction = PatioFunctionDefinition.builder()
diff --git a/src/test/java/org/shedlang/compiler/patio/instructions/Patio.java b/src/test/java/org/shedlang/compiler/patio/instructions/Patio.java
index f8f8dbf6..d6d236c6 100644
--- a/src/test/java/org/shedlang/compiler/patio/instructions/Patio.java
+++ b/src/test/java/org/shedlang/compiler/patio/instructions/Patio.java
@@ -119,6 +119,10 @@ public class Patio {
         return PatioDataPtrConst.dataElement(name);
     }
 
+    public static PatioOperand dataPtrConst(PatioDataPtrValue value) {
+        return new PatioDataPtrConst(value);
+    }
+
     public static PatioInstruction dataPtrToInt(PatioLocalRef destination, PatioOperand value) {
         return new PatioDataPtrToInt(
             destination,
-- 
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