From 2b25a227dcae438ba94dbf5324a68b6953d25394 Mon Sep 17 00:00:00 2001
From: jdymitarai <o10040115@gmail.com>
Date: Tue, 15 Sep 2026 11:42:27 +0800
Subject: [PATCH] builtin: declare :list:member as ArgModeInputOutput (fixes
 #94)

---
 analysis/validation_test.go      | 10 ++++++++--
 builtin/builtin.go               |  2 +-
 engine/seminaivebottomup_test.go | 26 ++++++++++++++++++++++++++
 3 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/analysis/validation_test.go b/analysis/validation_test.go
index a08cb51..93fb082 100644
--- a/analysis/validation_test.go
+++ b/analysis/validation_test.go
@@ -18,7 +18,7 @@ import (
 	"bytes"
 	"embed"
 	"fmt"
-	"path/filepath"
+	"path"
 	"strings"
 	"testing"
 
@@ -85,7 +85,7 @@ func TestCases(t *testing.T) {
 	for _, testCase := range entries {
 		t.Run(testCase.Name(), func(t *testing.T) {
 			file, err := testCases.ReadFile(
-				filepath.Join("test_cases", testCase.Name()))
+				path.Join("test_cases", testCase.Name()))
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -693,6 +693,12 @@ func TestBoundsAnalyzer(t *testing.T) {
 			makeSimpleDecl(atom("foo(X)"), ast.NumberBound),
 			makeSimpleDecl(atom("bar(Y)"), symbols.NewListType(ast.NumberBound)),
 		}),
+		newBoundsTestCase(t, []ast.Clause{
+			clause("foo(X) :- bar(X), :list:member(X, [/a, /b])."),
+		}, []ast.Decl{
+			makeSimpleDecl(atom("foo(X)"), ast.NameBound),
+			makeSimpleDecl(atom("bar(X)"), ast.NameBound),
+		}),
 		newBoundsTestCase(t, []ast.Clause{
 			clause("bar(T) :-	T = fn:string:concat(\"A\", 123)."),
 		}, []ast.Decl{
diff --git a/builtin/builtin.go b/builtin/builtin.go
index 0368760..7ead84f 100644
--- a/builtin/builtin.go
+++ b/builtin/builtin.go
@@ -51,7 +51,7 @@ var (
 		symbols.FloatLe:        {ast.ArgModeInput, ast.ArgModeInput},
 		symbols.FloatGt:        {ast.ArgModeInput, ast.ArgModeInput},
 		symbols.FloatGe:        {ast.ArgModeInput, ast.ArgModeInput},
-		symbols.ListMember:     {ast.ArgModeOutput, ast.ArgModeInput},
+		symbols.ListMember:     {ast.ArgModeInputOutput, ast.ArgModeInput},
 		symbols.WithinDistance: {ast.ArgModeInput, ast.ArgModeInput, ast.ArgModeInput},
 		symbols.MatchPair:      {ast.ArgModeInput, ast.ArgModeOutput, ast.ArgModeOutput},
 		symbols.MatchCons:      {ast.ArgModeInput, ast.ArgModeOutput, ast.ArgModeOutput},
diff --git a/engine/seminaivebottomup_test.go b/engine/seminaivebottomup_test.go
index e8aac8b..1ba49e0 100644
--- a/engine/seminaivebottomup_test.go
+++ b/engine/seminaivebottomup_test.go
@@ -210,6 +210,32 @@ func TestNegation(t *testing.T) {
 	}
 }
 
+func TestListMemberBound(t *testing.T) {
+	store := factstore.NewSimpleInMemoryStore()
+	prog := []ast.Clause{
+		clause("seen(/a)."),
+		clause("seen(/c)."),
+		clause("approved(X) :- seen(X), :list:member(X, [/a, /b])."),
+		clause("is_member() :- :list:member(/a, [/a, /b])."),
+	}
+	if err := analyzeAndEvalProgram(t, prog, store); err != nil {
+		t.Fatalf("Program evaluation failed: %v", err)
+	}
+	expected := []ast.Atom{
+		atom("approved(/a)"),
+		atom("is_member()"),
+	}
+	for _, a := range expected {
+		if !store.Contains(a) {
+			t.Errorf("expected fact %v not found", a)
+		}
+	}
+	unexpected := atom("approved(/c)")
+	if store.Contains(unexpected) {
+		t.Errorf("unexpected fact %v found", unexpected)
+	}
+}
+
 func TestNegationOrder(t *testing.T) {
 	store := factstore.NewSimpleInMemoryStore()
 	negationProgram := []ast.Clause{