diff --git a/lib/primes.mbt b/lib/primes.mbt
index 7c31af5..35ba9cb 100644
--- a/lib/primes.mbt
+++ b/lib/primes.mbt
@@ -19,6 +19,24 @@ pub fn to_json(self : Cirru) -> Json {
   }
 }
 
+pub impl @json.FromJson for Cirru with from_json(json, path) {
+  match json {
+    String(a) => {
+      Cirru::Leaf(a)
+    }
+    Array(xs) => {
+    let ys = []
+      for idx, x in xs {
+        let v = @json.FromJson::from_json!(x, path.add_index(idx))
+        ys.push(v)
+      }
+      Cirru::List(ys)
+    }
+    // _ => @json.decode_error!((path, "Char::from_json: expected string"))
+    _ => raise @json.JsonDecodeError((path, "Cirru::from_json: expected string or array"))
+  }
+}
+
 fn Cirru::default() -> Cirru {
   Cirru::List(Array::new())
 }
diff --git a/main/main.mbt b/main/main.mbt
index 6166897..7fff491 100644
--- a/main/main.mbt
+++ b/main/main.mbt
@@ -1,4 +1,4 @@
-fn main {
+pub fn main_parser() -> Unit {
   // let tree = @lib.parse?("DEMO")
   // match tree {
   //   Result::Ok(tree) => {
@@ -23,6 +23,26 @@ fn main {
   }
 }
 
+fn main {
+  let demo = "folding"
+  let demo_file = fsReadSync("./test/cirru/\{demo}.cirru")
+  let json_file = fsReadSync("./test/data/\{demo}.json")
+
+  let defined=   @json.parse?(json_file).unwrap()
+  let tree: Array[@lib.Cirru] = @json.from_json?(defined).unwrap()
+  println("TREE:")
+  for item in tree {
+    println(item.to_json().stringify())
+  }
+
+  let ret = @lib.format?(tree, {use_inline: false}).unwrap()
+  println("Generated:")
+  println(ret)
+  println("Expected:")
+  println(demo_file)
+  println("")
+}
+
 pub extern "js" fn fsReadSync(path : String) -> String =
   #|(path) => {
   #|  const fs = require("node:fs");