Add Str::index and Str::to_list

Strings can be converted to a list of strings, split up by character.

Strings can also be indexed by character.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/obj/str.rs

@@ -101,6 +101,14 @@ impl Str {
         }
     }
 
+    pub(crate) fn to_list(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
+        let this = vm.frame_stack()[0].clone();
+        let list_items = with_obj_downcast(this, |str: &Str| {
+            str.str_value().chars().map(|c| Str::create(c)).collect()
+        });
+        List::create(list_items).into()
+    }
+
     pub(crate) fn len(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
         let len = with_obj_downcast(vm.frame_stack()[0].clone(), |str_inst: &Str| {
             str_inst.str_value().len() as i64
@@ -141,4 +149,38 @@ impl Str {
         let new = format!("{}", lhs.borrow()).repeat(repeat_count);
         Str::create(new).into()
     }
+
+    pub(crate) fn index(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
+        let this = vm.frame_stack()[0].clone();
+        let index_obj = vm.frame_stack()[1].clone();
+
+        let index = if let Some(index_obj) = index_obj.borrow().as_any().downcast_ref::<Int>() {
+            index_obj.int_value()
+        } else {
+            // TODO Str::index - throw an exception when the index object is not an integer
+            // BLOCKED-ON: exceptions
+            todo!("throw an exception when the index object is not an integer")
+        };
+
+        // TODO Str::index - maybe there is a way we can optimize this, because both getting the
+        // length in characters plus getting the nth character can be slow if we're doing UTF-8
+        // lookups. Maybe cache the length of the string in the Str struct?
+        let c = with_obj_downcast(this, |str: &Str| {
+            let len = str.str_value().chars().count();
+            let mut index = index;
+            if index < 0 {
+                index = len as i64 + index;
+            }
+
+            if index < 0 || index as usize >= len {
+                // TODO Str::index - throw an exception when the index is out of range
+                // BLOCKED-ON: exceptions
+                todo!("throw an exception when the str index is out of range")
+            } else {
+                str.str_value().chars().nth(index as usize).unwrap()
+            }
+        });
+
+        Str::create(c).into()
+    }
 }

src/obj/ty.rs

@@ -157,6 +157,7 @@ pub fn init_types() {
             to_bool => BuiltinFunction::create("to_bool", BaseObj::to_bool, 1),
             to_int => BuiltinFunction::create("to_int", BaseObj::not_implemented_un, 1),
             to_float => BuiltinFunction::create("to_float", BaseObj::not_implemented_un, 1),
+            to_list => BuiltinFunction::create("to_list", BaseObj::not_implemented_un, 1),
             len => BuiltinFunction::create("len", BaseObj::not_implemented_un, 1),
 
             // Constructor
@@ -204,6 +205,7 @@ pub fn init_types() {
             to_str => BuiltinFunction::create("to_str", Str::to_str, 1),
             to_int => BuiltinFunction::create("to_int", Str::to_int, 1),
             to_float => BuiltinFunction::create("to_float", Str::to_float, 1),
+            to_list => BuiltinFunction::create("to_list", Str::to_list, 1),
             len => BuiltinFunction::create("len", Str::len, 1),
 
             // Constructor
@@ -214,6 +216,8 @@ pub fn init_types() {
             __add__ => BuiltinFunction::create("__add__", Str::add, 2),
             __mul__ => BuiltinFunction::create("__mul__", Str::mul, 2),
 
+            __index__ => BuiltinFunction::create("__index__", Str::index, 2),
+
             // Methods
             // TODO Str methods - .lower, .upper, .slice, etc
         },