diff --git a/argparse/parser_positionals.mbt b/argparse/parser_positionals.mbt
index 0e79d867f..44d168eb3 100644
--- a/argparse/parser_positionals.mbt
+++ b/argparse/parser_positionals.mbt
@@ -14,13 +14,9 @@
 
 ///|
 fn positional_args(args : Array[Arg]) -> Array[Arg] {
-  let ordered = []
-  for arg in args {
-    if arg.info is PositionalInfo(_) {
-      ordered.push(arg)
-    }
-  }
-  ordered
+  [
+    for arg in args if arg.info is PositionalInfo(_) => arg
+  ]
 }
 
 ///|
diff --git a/hashset/hashset.mbt b/hashset/hashset.mbt
index 4ba3437dd..90e5d5139 100644
--- a/hashset/hashset.mbt
+++ b/hashset/hashset.mbt
@@ -314,13 +314,9 @@ pub fn[K] HashSet::iter(self : HashSet[K]) -> Iter[K] {
 ///|
 /// Converts the hash set to an array.
 pub fn[K] HashSet::to_array(self : HashSet[K]) -> Array[K] {
-  let arr = Array::new(capacity=self.size)
-  for entry in self.entries {
-    if entry is Some({ key, .. }) {
-      arr.push(key)
-    }
-  }
-  arr
+  [
+    for entry in self.entries if entry is Some({ key, .. }) => key
+  ]
 }
 
 ///|
diff --git a/immut/sorted_set/immutable_set.mbt b/immut/sorted_set/immutable_set.mbt
index 18068f1aa..baef33676 100644
--- a/immut/sorted_set/immutable_set.mbt
+++ b/immut/sorted_set/immutable_set.mbt
@@ -791,11 +791,7 @@ pub impl[A : Show] Show for SortedSet[A] with output(self, logger) {
 
 ///|
 pub impl[A : ToJson] ToJson for SortedSet[A] with to_json(self) {
-  let capacity = self.iter().count()
-  guard capacity != 0 else { return Json::array([]) }
-  let jsons = Array::new(capacity~)
-  self.each(a => jsons.push(a.to_json()))
-  Json::array(jsons)
+  Json::array([ for a in self => a.to_json() ])
 }
 
 ///|
diff --git a/list/list.mbt b/list/list.mbt
index 95bfd2d10..6e775da62 100644
--- a/list/list.mbt
+++ b/list/list.mbt
@@ -94,13 +94,7 @@ pub impl[A : Show] Show for List[A] with output(xs, logger) {
 /// ToJson implementation for List.
 /// Converts a list to a JSON array.
 pub impl[A : ToJson] ToJson for List[A] with to_json(self) {
-  let capacity = self.length()
-  guard capacity != 0 else { return [] }
-  let jsons = Array::new(capacity~)
-  for a in self {
-    jsons.push(a.to_json())
-  }
-  Json::array(jsons)
+  Json::array([ for a in self => a.to_json() ])
 }
 
 ///|
diff --git a/sorted_map/deprecated.mbt b/sorted_map/deprecated.mbt
index f4012d07c..64ffdacbc 100644
--- a/sorted_map/deprecated.mbt
+++ b/sorted_map/deprecated.mbt
@@ -17,9 +17,9 @@
 #deprecated("Use `keys_as_iter` instead. `keys` will return `Iter[K]` instead of `Array[K]` in the future.")
 #coverage.skip
 pub fn[K, V] SortedMap::keys(self : SortedMap[K, V]) -> Array[K] {
-  let keys = Array::new(capacity=self.size)
-  self.each((k, _v) => keys.push(k))
-  keys
+  [
+    for k, _ in self => k
+  ]
 }
 
 ///|
@@ -27,7 +27,7 @@ pub fn[K, V] SortedMap::keys(self : SortedMap[K, V]) -> Array[K] {
 #deprecated("Use `values_as_iter` instead. `values` will return `Iter[V]` instead of `Array[V]` in the future.")
 #coverage.skip
 pub fn[K, V] SortedMap::values(self : SortedMap[K, V]) -> Array[V] {
-  let values = Array::new(capacity=self.size)
-  self.each((_k, v) => values.push(v))
-  values
+  [
+    for _, v in self => v
+  ]
 }
diff --git a/sorted_map/map.mbt b/sorted_map/map.mbt
index b153c93ae..0f1dac027 100644
--- a/sorted_map/map.mbt
+++ b/sorted_map/map.mbt
@@ -269,9 +269,9 @@ pub fn[K, V] SortedMap::values_as_iter(self : SortedMap[K, V]) -> Iter[V] {
 ///|
 /// Returns an array of all key-value pairs in ascending key order.
 pub fn[K, V] SortedMap::to_array(self : SortedMap[K, V]) -> Array[(K, V)] {
-  let arr = Array::new(capacity=self.size)
-  self.each((k, v) => arr.push((k, v)))
-  arr
+  [
+    for kv in self => kv
+  ]
 }
 
 ///|