diff --git a/src/main.rs b/src/main.rs
index 041a181..5948c59 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -216,7 +216,9 @@ fn main() -> Result<(), ()> {
     let exec_module =
         compile(&compilation_params, module, &mut env.environment).expect("no compilation error");
 
-    code_dump(&exec_module.code, &exec_module.funs);
+    let mut out = String::new();
+    code_dump(&mut out, &exec_module.code, &exec_module.funs).expect("writing to string work");
+    println!("{}", out);
 
     let ee = env.finalize();
 
diff --git a/werbolg-compile/src/compile.rs b/werbolg-compile/src/compile.rs
index 0009a90..dfbcd64 100644
--- a/werbolg-compile/src/compile.rs
+++ b/werbolg-compile/src/compile.rs
@@ -5,6 +5,7 @@ use super::instructions::*;
 use super::symbols::*;
 use super::CompilationError;
 use super::CompilationParams;
+use alloc::{vec, vec::Vec};
 use werbolg_core as ir;
 use werbolg_core::{ConstrId, FunId, GlobalId, Ident, LitId, NifId, Span};
 
diff --git a/werbolg-compile/src/defs.rs b/werbolg-compile/src/defs.rs
index 6adb791..75cffce 100644
--- a/werbolg-compile/src/defs.rs
+++ b/werbolg-compile/src/defs.rs
@@ -1,5 +1,6 @@
 use super::code::InstructionAddress;
 use super::instructions::*;
+use alloc::vec::Vec;
 use werbolg_core::{ConstrId, Ident};
 
 #[derive(Copy, Clone, Debug)]
diff --git a/werbolg-compile/src/instructions.rs b/werbolg-compile/src/instructions.rs
index 57c7f6d..3346451 100644
--- a/werbolg-compile/src/instructions.rs
+++ b/werbolg-compile/src/instructions.rs
@@ -1,6 +1,7 @@
 use super::code::InstructionDiff;
 use werbolg_core::{ConstrId, FunId, GlobalId, LitId, NifId};
 
+/// Instruction for execution
 #[derive(Clone, Debug)]
 pub enum Instruction {
     /// Push a literal value on the stack
@@ -15,7 +16,7 @@ pub enum Instruction {
     FetchStackParam(ParamBindIndex),
     /// Fetch from the localstack values (which is relative and after SP)
     FetchStackLocal(LocalBindIndex),
-    /// Access a field in a structure value as stack[top]
+    /// Access a field in a structure value as stack\[top\]
     AccessField(ConstrId, StructFieldIndex),
     /// Bind Locally a value
     LocalBind(LocalBindIndex),
@@ -27,20 +28,30 @@ pub enum Instruction {
     Call(CallArity),
     /// Jump by N instructions
     Jump(InstructionDiff),
-    /// Jump by N instructions if stack[top] is true
+    /// Jump by N instructions if stack\[top\] is true
     CondJump(InstructionDiff),
     /// Return from call
     Ret,
 }
 
+/// The index of locally (in the context of a function) bind value
+///
+/// This is limited (arbitrarily) to a maximum of 65535 values
 #[derive(Clone, Copy, Debug)]
 pub struct LocalBindIndex(pub u16);
 
+/// the index of function parameter
 #[derive(Clone, Copy, Debug)]
 pub struct ParamBindIndex(pub u8);
 
+/// A field in a structured indexed by its order in the structure
+///
+/// This is limited (arbitrarily) to a maximum of 255
 #[derive(Clone, Copy, Debug)]
 pub struct StructFieldIndex(pub u8);
 
+/// The arity (number of parameter) of a function.
+///
+/// This is limited (arbitrarily) to a maximum of 255
 #[derive(Clone, Copy, Debug)]
 pub struct CallArity(pub u8);
diff --git a/werbolg-compile/src/lib.rs b/werbolg-compile/src/lib.rs
index 54a5c98..7701fde 100644
--- a/werbolg-compile/src/lib.rs
+++ b/werbolg-compile/src/lib.rs
@@ -1,3 +1,5 @@
+#![no_std]
+
 extern crate alloc;
 
 mod bindings;
@@ -22,6 +24,9 @@ use bindings::BindingsStack;
 pub use environ::Environment;
 use symbols::{IdVec, IdVecAfter, SymbolsTable, SymbolsTableData};
 
+use alloc::format;
+use core::fmt::Write;
+
 #[derive(Debug)]
 pub enum CompilationError {
     DuplicateSymbol(Ident),
@@ -98,7 +103,11 @@ pub fn compile<'a, L: Clone + Eq + core::hash::Hash>(
     })
 }
 
-pub fn code_dump(code: &IdVec<InstructionAddress, Instruction>, fundefs: &IdVec<FunId, FunDef>) {
+pub fn code_dump<W: Write>(
+    writer: &mut W,
+    code: &IdVec<InstructionAddress, Instruction>,
+    fundefs: &IdVec<FunId, FunDef>,
+) -> Result<(), core::fmt::Error> {
     let mut place = hashbrown::HashMap::new();
     for (funid, fundef) in fundefs.iter() {
         place.insert(fundef.code_pos, funid);
@@ -107,7 +116,8 @@ pub fn code_dump(code: &IdVec<InstructionAddress, Instruction>, fundefs: &IdVec<
     for (ia, stmt) in code.iter() {
         if let Some(funid) = place.get(&ia) {
             let fundef = &fundefs[*funid];
-            println!(
+            write!(
+                writer,
                 "[{} local-stack={}]",
                 fundef
                     .name
@@ -115,8 +125,9 @@ pub fn code_dump(code: &IdVec<InstructionAddress, Instruction>, fundefs: &IdVec<
                     .map(|n| format!("{:?}", n))
                     .unwrap_or(format!("{:?}", funid)),
                 fundef.stack_size.0
-            );
+            )?;
         }
-        println!("{}  {:?}", ia, stmt)
+        write!(writer, "{}  {:?}", ia, stmt)?
     }
+    Ok(())
 }