add first version of List.dropAt

* adds an implementation with no uniqueness/mutability

compiler/gen_llvm/src/llvm/build_list.rs

@@ -297,7 +297,7 @@ pub fn list_swap<'a, 'ctx, 'env>(
     )
 }
 
-/// List.drop : List elem, Nat, Nat -> List elem
+/// List.drop : List elem, Nat -> List elem
 pub fn list_drop<'a, 'ctx, 'env>(
     env: &Env<'a, 'ctx, 'env>,
     layout_ids: &mut LayoutIds<'a>,
@@ -319,6 +319,29 @@ pub fn list_drop<'a, 'ctx, 'env>(
     )
 }
 
+// GIESCH ask about how this calling/linking to compiled zig works
+/// List.dropAt : List elem, Nat -> List elem
+pub fn list_drop_at<'a, 'ctx, 'env>(
+    env: &Env<'a, 'ctx, 'env>,
+    layout_ids: &mut LayoutIds<'a>,
+    original_wrapper: StructValue<'ctx>,
+    count: IntValue<'ctx>,
+    element_layout: &Layout<'a>,
+) -> BasicValueEnum<'ctx> {
+    let dec_element_fn = build_dec_wrapper(env, layout_ids, element_layout);
+    call_bitcode_fn_returns_list(
+        env,
+        &[
+            pass_list_cc(env, original_wrapper.into()),
+            env.alignment_intvalue(element_layout),
+            layout_width(env, element_layout),
+            count.into(),
+            dec_element_fn.as_global_value().as_pointer_value().into(),
+        ],
+        bitcode::LIST_DROP_AT,
+    )
+}
+
 /// List.set : List elem, Nat, elem -> List elem
 pub fn list_set<'a, 'ctx, 'env>(
     env: &Env<'a, 'ctx, 'env>,