diff --git a/distribution/std-lib/Base/src/Data/Json.enso b/distribution/std-lib/Base/src/Data/Json.enso
index fef8615c5db..c7707c83d8f 100644
--- a/distribution/std-lib/Base/src/Data/Json.enso
+++ b/distribution/std-lib/Base/src/Data/Json.enso
@@ -64,7 +64,7 @@ type Json
 
     ## Renders this JSON into an RFC-8259 compliant text.
     to_text : Text
-    to_text = Internal.render_helper this
+    to_text = Internal.render_helper "" this
 
     ## Recursively unwraps the JSON value into primitive values.
     unwrap : Any
diff --git a/distribution/std-lib/Base/src/Data/Json/Internal.enso b/distribution/std-lib/Base/src/Data/Json/Internal.enso
index a8f0bdd7a1d..8477d667c68 100644
--- a/distribution/std-lib/Base/src/Data/Json/Internal.enso
+++ b/distribution/std-lib/Base/src/Data/Json/Internal.enso
@@ -113,22 +113,34 @@ mk_consumer =
     Consumer child val
 
 ## Helper method for printing JSON values to Text.
-render_helper json = case json of
+render_helper builder json = case json of
     Object fields ->
-        fs = fields.to_vector.map item->
-            key = item.at 0
-            value = item.at 1
-            value_json = here.render_helper value
-            key_json = Printer.json_escape [key]
-            key_json + ":" + value_json
-        "{" + (fs.join ",") + "}"
+        r = Ref.new ""
+        render_key_value acc key value =
+            separator = Ref.get r
+            Ref.put r ","
+            val = here.render_helper "" value
+            acc + separator + (Printer.json_escape [key]) + ":" + val
+        arr = fields.fold_with_key "" render_key_value
+        builder + "{" + arr + "}"
     Array items ->
-        its = items.map here.render_helper
-        "[" + (its.join ",") + "]"
-    String value -> Printer.json_escape [value]
-    Number value -> value.to_text
-    Boolean value -> if value then "true" else "false"
-    Null -> "null"
+        r = Ref.new ""
+        render_array_element acc element =
+            separator = Ref.get r
+            Ref.put r ","
+            val = here.render_helper "" element
+            acc + separator + val
+        arr = items.fold "" render_array_element
+        builder + "[" + arr + "]"
+    String value ->
+        builder + (Printer.json_escape [value])
+    Number value ->
+        builder + value.to_text
+    Boolean value ->
+        val = if value then "true" else "false"
+        builder + val
+    Null ->
+        builder + "null"
 
 ## Helper method for converting JSON objects into arbitrary types.
 
diff --git a/distribution/std-lib/Base/src/Data/Map.enso b/distribution/std-lib/Base/src/Data/Map.enso
index 2ed811139f8..b4b03ef3733 100644
--- a/distribution/std-lib/Base/src/Data/Map.enso
+++ b/distribution/std-lib/Base/src/Data/Map.enso
@@ -163,8 +163,8 @@ type Map
     each_with_key function =
         go map = case map of
             Bin _ k v l r ->
-                function k v
                 go l
+                function k v
                 go r
                 Nothing
             Tip -> Nothing
@@ -174,7 +174,7 @@ type Map
 
        > Example
          Summing all of the values in the map `m`.
-             m.fold (+)
+             m.fold 0 (+)
     fold : Any -> (Any -> Any -> Any) -> Any
     fold init function =
         go map init = case map of
@@ -189,7 +189,7 @@ type Map
 
        > Example
          Sum the keys and values in the map `m`.
-             m.fold_with_key (l -> k -> v -> l + k + v)
+             m.fold_with_key 0 (l -> k -> v -> l + k + v)
     fold_with_key : Any -> (Any -> Any -> Any -> Any) -> Any
     fold_with_key init function =
         go map init = case map of
@@ -235,4 +235,3 @@ type Map
             Tip -> Nothing
         to_vector_with_builder this
         builder.to_vector
-