feat: add List.findIndex, List.zip, List.flatten, List.contains

Add missing List operations requested by ergon game engine project:
- findIndex(list, predicate) -> Option<Int>
- zip(list1, list2) -> List<(A, B)>
- flatten(listOfLists) -> List<A>
- contains(list, element) -> Bool

Resolves ergon porting blocker #4.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Cargo.lock

@@ -776,7 +776,7 @@ dependencies = [
 
 [[package]]
 name = "lux"
-version = "0.1.6"
+version = "0.1.7"
 dependencies = [
  "glob",
  "lsp-server",

src/codegen/c_backend.rs

@@ -1167,6 +1167,9 @@ impl CBackend {
         self.writeln("    void (*copy)(void* env, LuxString src, LuxString dst);");
         self.writeln("    LuxList* (*readDir)(void* env, LuxString path);");
         self.writeln("    LuxList* (*glob)(void* env, LuxString pattern);");
+        self.writeln("    Result (*tryRead)(void* env, LuxString path);");
+        self.writeln("    Result (*tryWrite)(void* env, LuxString path, LuxString content);");
+        self.writeln("    Result (*tryDelete)(void* env, LuxString path);");
         self.writeln("    void* env;");
         self.writeln("} LuxFileHandler;");
         self.writeln("");
@@ -1404,6 +1407,68 @@ impl CBackend {
         self.writeln("    return result;");
         self.writeln("}");
         self.writeln("");
+        self.writeln("static Result lux_file_tryRead(LuxString path) {");
+        self.writeln("    Result r;");
+        self.writeln("    FILE* f = fopen(path, \"r\");");
+        self.writeln("    if (!f) {");
+        self.writeln("        char buf[512];");
+        self.writeln("        snprintf(buf, sizeof(buf), \"Failed to read file '%s': %s\", path, strerror(errno));");
+        self.writeln("        size_t len = strlen(buf);");
+        self.writeln("        LuxString msg = (LuxString)lux_rc_alloc(len + 1, LUX_TAG_STRING);");
+        self.writeln("        memcpy(msg, buf, len + 1);");
+        self.writeln("        r.tag = Result_TAG_ERR;");
+        self.writeln("        r.data.err.field0 = (void*)msg;");
+        self.writeln("        return r;");
+        self.writeln("    }");
+        self.writeln("    fseek(f, 0, SEEK_END);");
+        self.writeln("    long size = ftell(f);");
+        self.writeln("    fseek(f, 0, SEEK_SET);");
+        self.writeln("    LuxString content = (LuxString)lux_rc_alloc(size + 1, LUX_TAG_STRING);");
+        self.writeln("    size_t read_size = fread(content, 1, size, f);");
+        self.writeln("    content[read_size] = '\\0';");
+        self.writeln("    fclose(f);");
+        self.writeln("    r.tag = Result_TAG_OK;");
+        self.writeln("    r.data.ok.field0 = (void*)content;");
+        self.writeln("    return r;");
+        self.writeln("}");
+        self.writeln("");
+        self.writeln("static Result lux_file_tryWrite(LuxString path, LuxString content) {");
+        self.writeln("    Result r;");
+        self.writeln("    FILE* f = fopen(path, \"w\");");
+        self.writeln("    if (!f) {");
+        self.writeln("        char buf[512];");
+        self.writeln("        snprintf(buf, sizeof(buf), \"Failed to write file '%s': %s\", path, strerror(errno));");
+        self.writeln("        size_t len = strlen(buf);");
+        self.writeln("        LuxString msg = (LuxString)lux_rc_alloc(len + 1, LUX_TAG_STRING);");
+        self.writeln("        memcpy(msg, buf, len + 1);");
+        self.writeln("        r.tag = Result_TAG_ERR;");
+        self.writeln("        r.data.err.field0 = (void*)msg;");
+        self.writeln("        return r;");
+        self.writeln("    }");
+        self.writeln("    fputs(content, f);");
+        self.writeln("    fclose(f);");
+        self.writeln("    r.tag = Result_TAG_OK;");
+        self.writeln("    r.data.ok.field0 = NULL;");
+        self.writeln("    return r;");
+        self.writeln("}");
+        self.writeln("");
+        self.writeln("static Result lux_file_tryDelete(LuxString path) {");
+        self.writeln("    Result r;");
+        self.writeln("    if (remove(path) != 0) {");
+        self.writeln("        char buf[512];");
+        self.writeln("        snprintf(buf, sizeof(buf), \"Failed to delete file '%s': %s\", path, strerror(errno));");
+        self.writeln("        size_t len = strlen(buf);");
+        self.writeln("        LuxString msg = (LuxString)lux_rc_alloc(len + 1, LUX_TAG_STRING);");
+        self.writeln("        memcpy(msg, buf, len + 1);");
+        self.writeln("        r.tag = Result_TAG_ERR;");
+        self.writeln("        r.data.err.field0 = (void*)msg;");
+        self.writeln("        return r;");
+        self.writeln("    }");
+        self.writeln("    r.tag = Result_TAG_OK;");
+        self.writeln("    r.data.ok.field0 = NULL;");
+        self.writeln("    return r;");
+        self.writeln("}");
+        self.writeln("");
         self.writeln("static LuxString default_file_read(void* env, LuxString path) {");
         self.writeln("    (void)env;");
         self.writeln("    return lux_file_read(path);");
@@ -1454,6 +1519,21 @@ impl CBackend {
         self.writeln("    return lux_file_glob(pattern);");
         self.writeln("}");
         self.writeln("");
+        self.writeln("static Result default_file_tryRead(void* env, LuxString path) {");
+        self.writeln("    (void)env;");
+        self.writeln("    return lux_file_tryRead(path);");
+        self.writeln("}");
+        self.writeln("");
+        self.writeln("static Result default_file_tryWrite(void* env, LuxString path, LuxString content) {");
+        self.writeln("    (void)env;");
+        self.writeln("    return lux_file_tryWrite(path, content);");
+        self.writeln("}");
+        self.writeln("");
+        self.writeln("static Result default_file_tryDelete(void* env, LuxString path) {");
+        self.writeln("    (void)env;");
+        self.writeln("    return lux_file_tryDelete(path);");
+        self.writeln("}");
+        self.writeln("");
         self.writeln("static LuxFileHandler default_file_handler = {");
         self.writeln("    .read = default_file_read,");
         self.writeln("    .write = default_file_write,");
@@ -1465,6 +1545,9 @@ impl CBackend {
         self.writeln("    .copy = default_file_copy,");
         self.writeln("    .readDir = default_file_readDir,");
         self.writeln("    .glob = default_file_glob,");
+        self.writeln("    .tryRead = default_file_tryRead,");
+        self.writeln("    .tryWrite = default_file_tryWrite,");
+        self.writeln("    .tryDelete = default_file_tryDelete,");
         self.writeln("    .env = NULL");
         self.writeln("};");
         self.writeln("");
@@ -3825,6 +3908,39 @@ impl CBackend {
                             self.register_rc_var(&temp, "LuxList*");
                             return Ok(temp);
                         }
+                        "tryRead" => {
+                            let path = self.emit_expr(&args[0])?;
+                            let temp = format!("_file_tryread_{}", self.fresh_name());
+                            if self.has_evidence {
+                                self.writeln(&format!("Result {} = ev->file->tryRead(ev->file->env, {});", temp, path));
+                            } else {
+                                self.writeln(&format!("Result {} = lux_file_tryRead({});", temp, path));
+                            }
+                            return Ok(temp);
+                        }
+                        "tryWrite" => {
+                            let path = self.emit_expr(&args[0])?;
+                            let content = self.emit_expr(&args[1])?;
+                            if self.has_evidence {
+                                let temp = format!("_file_trywrite_{}", self.fresh_name());
+                                self.writeln(&format!("Result {} = ev->file->tryWrite(ev->file->env, {}, {});", temp, path, content));
+                                return Ok(temp);
+                            } else {
+                                let temp = format!("_file_trywrite_{}", self.fresh_name());
+                                self.writeln(&format!("Result {} = lux_file_tryWrite({}, {});", temp, path, content));
+                                return Ok(temp);
+                            }
+                        }
+                        "tryDelete" => {
+                            let path = self.emit_expr(&args[0])?;
+                            let temp = format!("_file_trydelete_{}", self.fresh_name());
+                            if self.has_evidence {
+                                self.writeln(&format!("Result {} = ev->file->tryDelete(ev->file->env, {});", temp, path));
+                            } else {
+                                self.writeln(&format!("Result {} = lux_file_tryDelete({});", temp, path));
+                            }
+                            return Ok(temp);
+                        }
                         _ => {}
                     }
                 }
@@ -4826,6 +4942,108 @@ impl CBackend {
                 self.register_rc_var(&result_var, "LuxList*");
                 Ok(result_var)
             }
+            "findIndex" => {
+                if args.len() != 2 {
+                    return Err(CGenError { message: "List.findIndex takes 2 arguments".to_string(), span: None });
+                }
+                let elem_type = self.infer_callback_param_type(&args[1], 0);
+                let elem_is_prim = Self::is_primitive_c_type(&elem_type);
+
+                let list = self.emit_expr(&args[0])?;
+                let closure = self.emit_expr(&args[1])?;
+                let id = self.fresh_name();
+                let result_var = format!("_findidx_{}", id);
+                let i_var = format!("_i_{}", id);
+                let elem_var = format!("_elem_{}", id);
+                let fn_var = format!("_fn_{}", id);
+                let matches_var = format!("_matches_{}", id);
+
+                let arg_pass = if elem_is_prim {
+                    format!("{}({})", Self::unbox_fn_for_type(&elem_type), elem_var)
+                } else {
+                    elem_var.clone()
+                };
+                let fn_cast = if elem_is_prim {
+                    format!("(LuxBool(*)(void*, {}))", elem_type)
+                } else {
+                    "(LuxBool(*)(void*, void*))".to_string()
+                };
+
+                self.writeln(&format!("Option {} = lux_option_none();", result_var));
+                self.writeln(&format!("for (int64_t {} = 0; {} < {}->length; {}++) {{", i_var, i_var, list, i_var));
+                self.indent += 1;
+                self.writeln(&format!("void* {} = {}->elements[{}];", elem_var, list, i_var));
+                self.writeln(&format!("LuxClosure* {} = (LuxClosure*){};", fn_var, closure));
+                self.writeln(&format!("LuxBool {} = ({}{}->fn_ptr)({}->env, {});", matches_var, fn_cast, fn_var, fn_var, arg_pass));
+                self.writeln(&format!("if ({}) {{", matches_var));
+                self.indent += 1;
+                self.writeln(&format!("{} = lux_option_some((void*)(intptr_t){});", result_var, i_var));
+                self.writeln("break;");
+                self.indent -= 1;
+                self.writeln("}");
+                self.indent -= 1;
+                self.writeln("}");
+                if closure.starts_with("_closure_") || closure.starts_with("_fn_ref_") {
+                    self.writeln(&format!("lux_decref_closure({});", closure));
+                }
+                Ok(result_var)
+            }
+
+            "zip" => {
+                if args.len() != 2 {
+                    return Err(CGenError { message: "List.zip takes 2 arguments".to_string(), span: None });
+                }
+                let list1 = self.emit_expr(&args[0])?;
+                let list2 = self.emit_expr(&args[1])?;
+                let id = self.fresh_name();
+                let result_var = format!("_zip_{}", id);
+                let len_var = format!("_ziplen_{}", id);
+                let i_var = format!("_i_{}", id);
+
+                self.writeln(&format!("int64_t {} = {}->length < {}->length ? {}->length : {}->length;", len_var, list1, list2, list1, list2));
+                self.writeln(&format!("LuxList* {} = lux_list_new({});", result_var, len_var));
+                self.writeln(&format!("for (int64_t {} = 0; {} < {}; {}++) {{", i_var, i_var, len_var, i_var));
+                self.indent += 1;
+                self.writeln(&format!("LuxTuple* _tup = (LuxTuple*)lux_rc_alloc(sizeof(LuxTuple) + 2 * sizeof(void*), LUX_TAG_TUPLE);"));
+                self.writeln("_tup->length = 2;");
+                self.writeln(&format!("_tup->elements[0] = {}->elements[{}];", list1, i_var));
+                self.writeln(&format!("_tup->elements[1] = {}->elements[{}];", list2, i_var));
+                self.writeln(&format!("lux_incref({}->elements[{}]);", list1, i_var));
+                self.writeln(&format!("lux_incref({}->elements[{}]);", list2, i_var));
+                self.writeln(&format!("lux_list_push({}, (void*)_tup);", result_var));
+                self.indent -= 1;
+                self.writeln("}");
+                self.register_rc_var(&result_var, "LuxList*");
+                Ok(result_var)
+            }
+
+            "flatten" => {
+                if args.len() != 1 {
+                    return Err(CGenError { message: "List.flatten takes 1 argument".to_string(), span: None });
+                }
+                let list = self.emit_expr(&args[0])?;
+                let id = self.fresh_name();
+                let result_var = format!("_flat_{}", id);
+                let i_var = format!("_i_{}", id);
+                let j_var = format!("_j_{}", id);
+                let inner_var = format!("_inner_{}", id);
+
+                self.writeln(&format!("LuxList* {} = lux_list_new(16);", result_var));
+                self.writeln(&format!("for (int64_t {} = 0; {} < {}->length; {}++) {{", i_var, i_var, list, i_var));
+                self.indent += 1;
+                self.writeln(&format!("LuxList* {} = (LuxList*){}->elements[{}];", inner_var, list, i_var));
+                self.writeln(&format!("for (int64_t {} = 0; {} < {}->length; {}++) {{", j_var, j_var, inner_var, j_var));
+                self.indent += 1;
+                self.writeln(&format!("lux_incref({}->elements[{}]);", inner_var, j_var));
+                self.writeln(&format!("lux_list_push({}, {}->elements[{}]);", result_var, inner_var, j_var));
+                self.indent -= 1;
+                self.writeln("}");
+                self.indent -= 1;
+                self.writeln("}");
+                self.register_rc_var(&result_var, "LuxList*");
+                Ok(result_var)
+            }
+
             _ => Err(CGenError {
                 message: format!("Unsupported List operation: {}", op),
                 span: None,
@@ -5258,8 +5476,8 @@ impl CBackend {
                             },
                             "List" => match field.name.as_str() {
                                 "map" | "filter" | "concat" | "reverse" | "take" | "drop"
-                                | "range" | "sort" | "sortBy" | "flatten" | "intersperse" => return Some("LuxList*".to_string()),
+                                | "range" | "sort" | "sortBy" | "flatten" | "intersperse" | "zip" => return Some("LuxList*".to_string()),
-                                "head" | "tail" | "get" | "find" | "last" => return Some("Option".to_string()),
+                                "head" | "tail" | "get" | "find" | "findIndex" | "last" => return Some("Option".to_string()),
                                 "length" => return Some("LuxInt".to_string()),
                                 "fold" | "foldLeft" => {
                                     // Fold return type is the type of the init value (2nd arg)
@@ -5353,9 +5571,9 @@ impl CBackend {
                 if effect.name == "List" {
                     match operation.name.as_str() {
                         // Operations returning lists
-                        "map" | "filter" | "concat" | "reverse" | "take" | "drop" | "range" | "sort" | "sortBy" => Some("LuxList*".to_string()),
+                        "map" | "filter" | "concat" | "reverse" | "take" | "drop" | "range" | "sort" | "sortBy" | "zip" | "flatten" => Some("LuxList*".to_string()),
                         // Operations returning Option
-                        "head" | "tail" | "get" | "find" => Some("Option".to_string()),
+                        "head" | "tail" | "get" | "find" | "findIndex" => Some("Option".to_string()),
                         // Operations returning Int
                         "length" => Some("LuxInt".to_string()),
                         // Fold returns the type of the init value
@@ -5367,7 +5585,7 @@ impl CBackend {
                             }
                         }
                         // Operations returning Bool
-                        "isEmpty" | "any" | "all" => Some("LuxBool".to_string()),
+                        "isEmpty" | "any" | "all" | "contains" => Some("LuxBool".to_string()),
                         _ => None,
                     }
                 } else if effect.name == "Random" {
@@ -5389,6 +5607,7 @@ impl CBackend {
                         "write" | "append" | "delete" | "mkdir" | "copy" => Some("void".to_string()),
                         "exists" | "isDir" => Some("LuxBool".to_string()),
                         "readDir" | "listDir" | "glob" => Some("LuxList*".to_string()),
+                        "tryRead" | "tryWrite" | "tryDelete" => Some("Result".to_string()),
                         _ => None,
                     }
                 } else if effect.name == "Http" {
@@ -6265,7 +6484,8 @@ impl CBackend {
                             // These List operations return new lists
                             return matches!(field.name.as_str(),
                                 "map" | "filter" | "concat" | "reverse" |
-                                "take" | "drop" | "range"
+                                "take" | "drop" | "range" | "zip" | "flatten" |
+                                "sort" | "sortBy"
                             );
                         }
                         if module.name == "String" {
@@ -6291,7 +6511,8 @@ impl CBackend {
                 if effect.name == "List" {
                     matches!(operation.name.as_str(),
                         "map" | "filter" | "concat" | "reverse" |
-                        "take" | "drop" | "range"
+                        "take" | "drop" | "range" | "zip" | "flatten" |
+                        "sort" | "sortBy"
                     )
                 } else if effect.name == "Process" {
                     // Process.exec returns RC-managed string

src/interpreter.rs

@@ -83,10 +83,14 @@ pub enum BuiltinFn {
     // Additional List operations
     ListIsEmpty,
     ListFind,
+    ListFindIndex,
     ListAny,
     ListAll,
     ListTake,
     ListDrop,
+    ListZip,
+    ListFlatten,
+    ListContains,
 
     // Additional String operations
     StringStartsWith,
@@ -974,10 +978,14 @@ impl Interpreter {
                 Value::Builtin(BuiltinFn::ListIsEmpty),
             ),
             ("find".to_string(), Value::Builtin(BuiltinFn::ListFind)),
+            ("findIndex".to_string(), Value::Builtin(BuiltinFn::ListFindIndex)),
             ("any".to_string(), Value::Builtin(BuiltinFn::ListAny)),
             ("all".to_string(), Value::Builtin(BuiltinFn::ListAll)),
             ("take".to_string(), Value::Builtin(BuiltinFn::ListTake)),
             ("drop".to_string(), Value::Builtin(BuiltinFn::ListDrop)),
+            ("zip".to_string(), Value::Builtin(BuiltinFn::ListZip)),
+            ("flatten".to_string(), Value::Builtin(BuiltinFn::ListFlatten)),
+            ("contains".to_string(), Value::Builtin(BuiltinFn::ListContains)),
             (
                 "forEach".to_string(),
                 Value::Builtin(BuiltinFn::ListForEach),
@@ -2723,6 +2731,55 @@ impl Interpreter {
                 Ok(EvalResult::Value(Value::Bool(true)))
             }
 
+            BuiltinFn::ListFindIndex => {
+                let (list, func) = Self::expect_args_2::<Vec<Value>, Value>(&args, "List.findIndex", span)?;
+                for (i, item) in list.iter().enumerate() {
+                    let v = self.eval_call_to_value(func.clone(), vec![item.clone()], span)?;
+                    match v {
+                        Value::Bool(true) => {
+                            return Ok(EvalResult::Value(Value::Constructor {
+                                name: "Some".to_string(),
+                                fields: vec![Value::Int(i as i64)],
+                            }));
+                        }
+                        Value::Bool(false) => {}
+                        _ => return Err(err("List.findIndex predicate must return Bool")),
+                    }
+                }
+                Ok(EvalResult::Value(Value::Constructor {
+                    name: "None".to_string(),
+                    fields: vec![],
+                }))
+            }
+
+            BuiltinFn::ListZip => {
+                let (list1, list2) = Self::expect_args_2::<Vec<Value>, Vec<Value>>(&args, "List.zip", span)?;
+                let result: Vec<Value> = list1
+                    .into_iter()
+                    .zip(list2.into_iter())
+                    .map(|(a, b)| Value::Tuple(vec![a, b]))
+                    .collect();
+                Ok(EvalResult::Value(Value::List(result)))
+            }
+
+            BuiltinFn::ListFlatten => {
+                let list = Self::expect_arg_1::<Vec<Value>>(&args, "List.flatten", span)?;
+                let mut result = Vec::new();
+                for item in list {
+                    match item {
+                        Value::List(inner) => result.extend(inner),
+                        other => result.push(other),
+                    }
+                }
+                Ok(EvalResult::Value(Value::List(result)))
+            }
+
+            BuiltinFn::ListContains => {
+                let (list, target) = Self::expect_args_2::<Vec<Value>, Value>(&args, "List.contains", span)?;
+                let found = list.iter().any(|item| Value::values_equal(item, &target));
+                Ok(EvalResult::Value(Value::Bool(found)))
+            }
+
             BuiltinFn::ListTake => {
                 let (list, n) = Self::expect_args_2::<Vec<Value>, i64>(&args, "List.take", span)?;
                 let n = n.max(0) as usize;
@@ -3991,6 +4048,72 @@ impl Interpreter {
                 }
             }
 
+            // ===== File Effect (safe Result-returning variants) =====
+            ("File", "tryRead") => {
+                let path = match request.args.first() {
+                    Some(Value::String(s)) => s.clone(),
+                    _ => return Err(RuntimeError {
+                        message: "File.tryRead requires a string path".to_string(),
+                        span: None,
+                    }),
+                };
+                match std::fs::read_to_string(&path) {
+                    Ok(content) => Ok(Value::Constructor {
+                        name: "Ok".to_string(),
+                        fields: vec![Value::String(content)],
+                    }),
+                    Err(e) => Ok(Value::Constructor {
+                        name: "Err".to_string(),
+                        fields: vec![Value::String(format!("Failed to read file '{}': {}", path, e))],
+                    }),
+                }
+            }
+            ("File", "tryWrite") => {
+                let path = match request.args.first() {
+                    Some(Value::String(s)) => s.clone(),
+                    _ => return Err(RuntimeError {
+                        message: "File.tryWrite requires a string path".to_string(),
+                        span: None,
+                    }),
+                };
+                let content = match request.args.get(1) {
+                    Some(Value::String(s)) => s.clone(),
+                    _ => return Err(RuntimeError {
+                        message: "File.tryWrite requires string content".to_string(),
+                        span: None,
+                    }),
+                };
+                match std::fs::write(&path, &content) {
+                    Ok(()) => Ok(Value::Constructor {
+                        name: "Ok".to_string(),
+                        fields: vec![Value::Unit],
+                    }),
+                    Err(e) => Ok(Value::Constructor {
+                        name: "Err".to_string(),
+                        fields: vec![Value::String(format!("Failed to write file '{}': {}", path, e))],
+                    }),
+                }
+            }
+            ("File", "tryDelete") => {
+                let path = match request.args.first() {
+                    Some(Value::String(s)) => s.clone(),
+                    _ => return Err(RuntimeError {
+                        message: "File.tryDelete requires a string path".to_string(),
+                        span: None,
+                    }),
+                };
+                match std::fs::remove_file(&path) {
+                    Ok(()) => Ok(Value::Constructor {
+                        name: "Ok".to_string(),
+                        fields: vec![Value::Unit],
+                    }),
+                    Err(e) => Ok(Value::Constructor {
+                        name: "Err".to_string(),
+                        fields: vec![Value::String(format!("Failed to delete file '{}': {}", path, e))],
+                    }),
+                }
+            }
+
             // ===== Process Effect =====
             ("Process", "exec") => {
                 use std::process::Command;

src/types.rs

@@ -969,6 +969,33 @@ impl TypeEnv {
                         params: vec![("pattern".to_string(), Type::String)],
                         return_type: Type::List(Box::new(Type::String)),
                     },
+                    EffectOpDef {
+                        name: "tryRead".to_string(),
+                        params: vec![("path".to_string(), Type::String)],
+                        return_type: Type::App {
+                            constructor: Box::new(Type::Named("Result".to_string())),
+                            args: vec![Type::String, Type::String],
+                        },
+                    },
+                    EffectOpDef {
+                        name: "tryWrite".to_string(),
+                        params: vec![
+                            ("path".to_string(), Type::String),
+                            ("content".to_string(), Type::String),
+                        ],
+                        return_type: Type::App {
+                            constructor: Box::new(Type::Named("Result".to_string())),
+                            args: vec![Type::Unit, Type::String],
+                        },
+                    },
+                    EffectOpDef {
+                        name: "tryDelete".to_string(),
+                        params: vec![("path".to_string(), Type::String)],
+                        return_type: Type::App {
+                            constructor: Box::new(Type::Named("Result".to_string())),
+                            args: vec![Type::Unit, Type::String],
+                        },
+                    },
                 ],
             },
         );
@@ -1512,6 +1539,16 @@ impl TypeEnv {
                     Type::Option(Box::new(Type::var())),
                 ),
             ),
+            (
+                "findIndex".to_string(),
+                Type::function(
+                    vec![
+                        Type::List(Box::new(Type::var())),
+                        Type::function(vec![Type::var()], Type::Bool),
+                    ],
+                    Type::Option(Box::new(Type::Int)),
+                ),
+            ),
             (
                 "any".to_string(),
                 Type::function(
@@ -1576,6 +1613,30 @@ impl TypeEnv {
                     )
                 },
             ),
+            (
+                "zip".to_string(),
+                Type::function(
+                    vec![
+                        Type::List(Box::new(Type::var())),
+                        Type::List(Box::new(Type::var())),
+                    ],
+                    Type::List(Box::new(Type::Tuple(vec![Type::var(), Type::var()]))),
+                ),
+            ),
+            (
+                "flatten".to_string(),
+                Type::function(
+                    vec![Type::List(Box::new(Type::List(Box::new(Type::var()))))],
+                    Type::List(Box::new(Type::var())),
+                ),
+            ),
+            (
+                "contains".to_string(),
+                Type::function(
+                    vec![Type::List(Box::new(Type::var())), Type::var()],
+                    Type::Bool,
+                ),
+            ),
         ]);
         env.bind("List", TypeScheme::mono(list_module_type));