Add the tuple ability member to EncoderFormatting

crates/compiler/builtins/roc/Encode.roc

@@ -22,6 +22,7 @@ interface Encode
         list,
         record,
         tag,
+        tuple,
         custom,
         appendWith,
         append,
@@ -69,6 +70,7 @@ EncoderFormatting has
     string : Str -> Encoder fmt | fmt has EncoderFormatting
     list : List elem, (elem -> Encoder fmt) -> Encoder fmt | fmt has EncoderFormatting
     record : List { key : Str, value : Encoder fmt } -> Encoder fmt | fmt has EncoderFormatting
+    tuple : List (Encoder fmt) -> Encoder fmt | fmt has EncoderFormatting
     tag : Str, List (Encoder fmt) -> Encoder fmt | fmt has EncoderFormatting
 
 custom : (List U8, fmt -> List U8) -> Encoder fmt | fmt has EncoderFormatting

crates/compiler/builtins/roc/Json.roc

@@ -96,6 +96,7 @@ Json := {} has [
              string: encodeString,
              list: encodeList,
              record: encodeRecord,
+             tuple: encodeTuple,
              tag: encodeTag,
          },
          DecoderFormatting {
@@ -207,6 +208,25 @@ encodeRecord = \fields ->
 
         List.append bytesWithRecord (Num.toU8 '}')
 
+encodeTuple = \elems ->
+    Encode.custom \bytes, @Json {} ->
+        writeTuple = \{ buffer, elemsLeft }, elemEncoder ->
+            bufferWithElem =
+                appendWith buffer elemEncoder (@Json {})
+
+            bufferWithSuffix =
+                if elemsLeft > 1 then
+                    List.append bufferWithElem (Num.toU8 ',')
+                else
+                    bufferWithElem
+
+            { buffer: bufferWithSuffix, elemsLeft: elemsLeft - 1 }
+
+        bytesHead = List.append bytes (Num.toU8 '[')
+        { buffer: bytesWithRecord } = List.walk elems { buffer: bytesHead, elemsLeft: List.len elems } writeTuple
+
+        List.append bytesWithRecord (Num.toU8 ']')
+
 encodeTag = \name, payload ->
     Encode.custom \bytes, @Json {} ->
         # Idea: encode `A v1 v2` as `{"A": [v1, v2]}`