diff --git a/python-ffi/Data/Array.py b/python-ffi/Data/Array.py
index a2bf1c7..e3f03e2 100644
--- a/python-ffi/Data/Array.py
+++ b/python-ffi/Data/Array.py
@@ -6,7 +6,7 @@
 def _rangeImpl(start):
     def ap(end):
         step = 1 if start <= end else -1
-        return list(_buitins["range"](start, end + step, step))
+        return tuple(_buitins["range"](start, end + step, step))
 
     return ap
 
@@ -14,7 +14,7 @@ def ap(end):
 globals()["range"] = _rangeImpl
 
 
-replicate = lambda count: lambda value: [value for _ in _buitins["range"](count)]
+replicate = lambda count: lambda value: tuple([value for _ in _buitins["range"](count)])
 
 
 def _mkFromFoldableImpl():
@@ -37,7 +37,7 @@ def listToArray(lst):
         while xs is not None:
             result.append(xs.head)
             xs = xs.tail
-        return result
+        return tuple(result)
 
     def result(foldr):
         def ap(xs):
@@ -47,14 +47,17 @@ def ap(xs):
 
     return result
 
-
+# TODO: discuss performance consideration with alternative implementation
+# at least should we use 2-tuple instead of class?
+# current implementation is aiming to mimic JS implementation as much as possible
+# same problem in NonEmpty.Internal.py
 fromFoldableImpl = _mkFromFoldableImpl()
 
 length = lambda xs: len(xs)
 
-cons = lambda e: lambda l: [e, *l]
+cons = lambda e: lambda l: (e, *l)
 
-snoc = lambda xs: lambda x: [*xs, x]
+snoc = lambda xs: lambda x: (*xs, x)
 
 
 def unconsImpl(empty):
@@ -111,9 +114,11 @@ def findLastIndexImpl(just):
 def _insertAtImpl(just, nothing, i, a, l):
     if i < 0 or i > len(l):
         return nothing
+    # TODO: discuss performance consideration with alternative implementation
+    # (*l[i-1], a, *l[i:])
     ll = list(l)
     ll.insert(i, a)
-    return just(ll)
+    return just(tuple(ll))
 
 
 _insertAt = lambda just: lambda nothing: lambda i: lambda a: lambda l: _insertAtImpl(
@@ -137,24 +142,24 @@ def _updateAtImpl(just, nothing, i, a, l):
         return nothing
     ll = list(l)
     ll[i] = a
-    return just(ll)
+    return just(tuple(ll))
 
 
 _updateAt = lambda just: lambda nothing: lambda i: lambda a: lambda l: _updateAtImpl(
     just, nothing, i, a, l
 )
 
-reverse = lambda xs: list(reversed(xs))
+reverse = lambda xs: tuple(reversed(xs))
 
 
 def concat(xss):
     result = []
     for x in xss:
         result.extend(x)
-    return result
+    return tuple(result)
 
 
-filter = lambda f: lambda xs: list(_buitins["filter"](f, xs))
+filter = lambda f: lambda xs: tuple(_buitins["filter"](f, xs))
 
 
 def partition(f):
@@ -166,20 +171,22 @@ def result(xs):
                 yes.append(x)
             else:
                 no.append(x)
-        return {"yes": yes, "no": no}
+        return {"yes": tuple(yes), "no": tuple(no)}
 
     return result
 
 
-sortImpl = lambda f: lambda xs: sorted(
-    xs, key=functools.cmp_to_key(lambda a, b: f(a)(b))
+sortImpl = lambda f: lambda xs: tuple(
+    sorted(xs, key=functools.cmp_to_key(lambda a, b: f(a)(b)))
 )
 
 slice = lambda s: lambda e: lambda xs: xs[s:e]
 
-take = lambda n: lambda xs: xs[:max(n, 0)]
-drop = lambda n: lambda xs: xs[max(n, 0):]
+take = lambda n: lambda xs: xs[: max(n, 0)]
+drop = lambda n: lambda xs: xs[max(n, 0) :]
 
-zipWith = lambda f: lambda xs: lambda ys: list(map(lambda t: f(t[0])(t[1]), zip(xs, ys)))
+zipWith = lambda f: lambda xs: lambda ys: tuple(
+    map(lambda t: f(t[0])(t[1]), zip(xs, ys))
+)
 
 unsafeIndexImpl = lambda xs: lambda n: xs[n]
diff --git a/python-ffi/Data/Array/NonEmpty/Internal.py b/python-ffi/Data/Array/NonEmpty/Internal.py
index 2644f5b..0566c7a 100644
--- a/python-ffi/Data/Array/NonEmpty/Internal.py
+++ b/python-ffi/Data/Array/NonEmpty/Internal.py
@@ -42,7 +42,7 @@ def listToArray(lst):
         while xs is not emptyList:
             arr.append(xs.head)
             xs = xs.tail
-        return arr
+        return tuple(arr)
 
     def kernel(apply, map_, f):
         def buildFrom(x, ys):