diff --git a/src/ast_to_c.ml b/src/ast_to_c.ml
index bca0ea2..3e3bbe8 100644
--- a/src/ast_to_c.ml
+++ b/src/ast_to_c.ml
@@ -288,29 +288,28 @@ let rec cp_nodes fmt (nodes, h) =
 
 
 
-let dump_var_locations (st: node_states) =
+(** [dump_var_locations] dumps the internal tables to map the program variable
+  * (after all the passes) to their location in the final C program. *)
+let dump_var_locations fmt (st: node_states) =
+  Format.fprintf fmt "Tables mapping the AST Variables to the C variables:\n";
   Hashtbl.iter
     (fun n st ->
-      Format.printf "\n\n\tNODE: %s\n" n;
+      Format.fprintf fmt "  ∗ NODE: %s\n" n;
     Hashtbl.iter
     (fun (s, (ispre: bool)) ((arr: string), (idx: int)) ->
       match ispre with
-      | true -> Format.printf "PRE Variable %s stored as %s[%d]\n" s arr idx
-      | false -> Format.printf "    Variable %s stored as %s[%d]\n" s arr idx)
+      | true -> Format.fprintf fmt "    PRE Variable %s stored as %s[%d]\n" s arr idx
+      | false -> Format.fprintf fmt "        Variable %s stored as %s[%d]\n" s arr idx)
     st.nt_map)
-    st;
-    Format.printf "\n\n"
+    st
 
 
 
 (** main function that prints a C-code from a term of type [t_nodelist]. *)
-let ast_to_c (debug: bool) prog =
+let ast_to_c verbose debug prog =
+  verbose "Computation of the node_states";
   let prog_st_types = make_state_types prog in
-  let () =
-    if debug
-      then dump_var_locations prog_st_types
-      else ()
-    in
+  debug (Format.asprintf "%a" dump_var_locations prog_st_types);
   let prog: i_nodelist = ast_to_intermediate_ast prog prog_st_types in
   Format.printf "%a\n\n%a\n\n/* Nodes: */\n%a"
     cp_includes (Config.c_includes)
diff --git a/src/main.ml b/src/main.ml
index 83d407f..3711c06 100644
--- a/src/main.ml
+++ b/src/main.ml
@@ -9,24 +9,44 @@ let print_debug d s =
 let print_verbose v s =
   if v then Format.printf "\x1b[33;01;04mStatus:\x1b[0m %s\n" s else ()
 
+
+
+(** [exec_passes] executes the passes on the parsed typed-AST.
+  * A pass should return [Some program] in case of a success, and [None]
+  * otherwise.
+  *
+  * The function [exec_passes] returns the optionnal program returned by the
+  * last pass.
+  *
+  * A pass should never be interrupted by an exception. Nevertheless, we make
+  * sure that no pass raise one. *)
 let exec_passes ast verbose debug passes f =
   let rec aux ast = function
     | [] ->  f ast
     | (n, p) :: passes ->
         verbose (Format.asprintf "Executing pass %s:\n" n);
-        match p verbose debug ast with
-        | None -> (exit_error ("Error while in the pass "^n^".\n"); exit 0)
-        | Some ast -> (
-        debug (Format.asprintf "Current AST (after %s):\n%a\n" n Lustre_pp.pp_ast ast);
-        aux ast passes)
+        try
+        begin
+          match p verbose debug ast with
+          | None -> (exit_error ("Error while in the pass "^n^".\n"); exit 0)
+          | Some ast -> (
+            debug
+              (Format.asprintf
+                "Current AST (after %s):\n%a\n" n Lustre_pp.pp_ast ast);
+            aux ast passes)
+        end with
+        | _ -> failwith ("[main.ml] The pass "^n^" should have catched me!")
   in
   aux ast passes
 
 
+
 let _ =
   (** Usage and argument parsing. *)
-  let default_passes = ["remove_if"; "linearization_pre"; "linearization_tuples"; "linearization_app";
-    "equations_ordering"] in
+  let default_passes =
+    ["remove_if";
+      "linearization_pre"; "linearization_tuples"; "linearization_app";
+      "equations_ordering"] in
   let sanity_passes = ["chkvar_init_unicity"; "check_typing"] in
   let usage_msg =
     "Usage: main [-passes p1,...,pn] [-ast] [-verbose] [-debug] \
@@ -106,6 +126,11 @@ let _ =
       end
     in
 
+  (** Computes the list of passes to execute. If the [-test] flag is set, all
+    * sanity passes (ie. passes which do not modify the AST, but ensure its
+    * validity) are re-run after any other pass.
+    *
+    * Note: the sanity passes are always executed before any other. *)
   let passes =
     List.map
       (fun (pass: string) -> (pass,
@@ -129,6 +154,6 @@ let _ =
     else (
       if !nopopt
         then (fun _ -> ())
-        else Ast_to_c.ast_to_c !debug)
+        else Ast_to_c.ast_to_c print_verbose print_debug)
   end
 
diff --git a/src/passes.ml b/src/passes.ml
index 352bb65..0566934 100644
--- a/src/passes.ml
+++ b/src/passes.ml
@@ -4,6 +4,8 @@ open Ast
 open Passes_utils
 open Utils
 
+
+
 (** [pass_if_removal] replaces the `if` construct with `when` and `merge` ones.
   *
   *     [x1, ..., xn = if c then e_l else e_r;]
@@ -18,7 +20,8 @@ open Utils
   * order to have the expressions active at each step.
   *)
 let pass_if_removal verbose debug =
-  let varcount = ref 0 in
+  let varcount = ref 0 in (** new variables are called «_ifrem[varcount]» *)
+  (** Males a pattern (t_varlist) of fresh variables matching the type t *)
   let make_patt t: t_varlist =
     (t, List.fold_right
       (fun ty acc ->
@@ -33,11 +36,14 @@ let pass_if_removal verbose debug =
         nvar :: acc)
       t [])
   in
+  (** If a tuple contains a single element, it should not be. *)
   let simplify_tuple t =
     match t with
     | ETuple (t, [elt]) -> elt
     | _ -> t
   in
+  (** For each equation, build a list of equations and a new list of local
+    * variables as well as an updated version of the original equation. *)
   let rec aux_eq vars eq: t_eqlist * t_varlist * t_equation =
     let patt, expr = eq in
     match expr with
@@ -127,6 +133,7 @@ let pass_if_removal verbose debug =
         let eqs, vars, (_, e) = aux_eq vars (patt, e) in
         eqs, vars, (patt, EApp (t, n, e))
   in
+  (** For each node, apply the previous function to all equations. *)
   let aux_if_removal node =
     let new_equations, new_locvars =
       List.fold_left
@@ -139,7 +146,23 @@ let pass_if_removal verbose debug =
   in
   node_pass aux_if_removal
 
+
+
+(** [pass_linearization_tuples] transforms expressions of the form
+  *     (x1, ..., xn) = (e1, ..., em);
+  * into:
+  *     p1 = e1;
+  *       ...
+  *     pm = em;
+  * where flatten (p1, ..., pm) = x1, ..., xn
+  *
+  * Idem for tuples hidden behind merges and when:
+  *     patt = (...) when c;
+  *     patt = merge c (...) (...);
+  *)
 let pass_linearization_tuples verbose debug ast =
+  (** [split_tuple] takes an equation and produces an equation list
+    * corresponding to the [pi = ei;] above. *)
   let rec split_tuple (eq: t_equation): t_eqlist =
     let patt, expr = eq in
     match expr with
@@ -154,6 +177,9 @@ let pass_linearization_tuples verbose debug ast =
     | ETuple (_, []) -> []
     | _ -> [eq]
   in
+  (** For each node, apply the previous function to all equations.
+    * It builds fake equations in order to take care of tuples behind
+    *  merge/when. *)
   let aux_linearization_tuples node =
     let new_equations = List.flatten
      (List.map
@@ -186,8 +212,15 @@ let pass_linearization_tuples verbose debug ast =
   try node_pass aux_linearization_tuples ast with
   | PassExn err -> (debug err; None)
 
+
+
+(** [pass_linearization_app] makes sure that any argument to a function is
+  * either a variable, or of the form [pre _] (which will be translated as a
+  * variable in the final C code. *)
 let pass_linearization_app verbose debug =
-  let applin_count = ref 0 in
+  let applin_count = ref 0 in (* new variables are called «_applin[varcount]» *)
+  (** [aux_expr] recursively explores the AST in order to find applications, and
+    * adds the requires variables and equations. *)
   let rec aux_expr vars expr: t_eqlist * t_varlist * t_expression =
     match expr with
     | EConst _ | EVar   _ -> [], vars, expr
@@ -253,16 +286,13 @@ let pass_linearization_app verbose debug =
         eqs, vars, EApp (tout, n, ETuple (tin, l))
     | EApp _ -> failwith "[passes.ml] Should not happened (parser)"
   in
-  let aux vars eq =
-    let eqs, vars, expr = aux_expr vars (snd eq) in
-    (fst eq, expr) :: eqs, vars
-  in
+  (** [aux_linearization_app] applies the previous function to every equation *)
   let aux_linearization_app node =
     let new_equations, new_locvars =
       List.fold_left
         (fun (eqs, vars) eq ->
-          let es, vs = aux vars eq in
-          es @ eqs, vs)
+          let eqs', vars, expr = aux_expr vars (snd eq) in
+          (fst eq, expr) :: eqs' @ eqs, vars)
         ([], node.n_local_vars)
         node.n_equations
       in
@@ -270,6 +300,8 @@ let pass_linearization_app verbose debug =
   in
   node_pass aux_linearization_app
 
+
+
 let chkvar_init_unicity verbose debug : t_nodelist -> t_nodelist option =
   let aux (node: t_node) : t_node option =
     let incr_aux h n =
@@ -363,8 +395,11 @@ let pass_linearization_pre verbose debug =
       | EVar _ -> [], vars, expr
       | EMonOp (t, op, e) ->
           begin
-          match op with
-          | MOp_pre ->
+          match op, e with
+          | MOp_pre, EVar _ ->
+              let eqs, vars, e = pre_aux_expression vars e in
+              eqs, vars, EMonOp (t, op, e)
+          | MOp_pre, _ ->
               let eqs, vars, e = pre_aux_expression vars e in
               let nvar: string = fresh_var_name vars 6 in
               let nvar = match t with
@@ -376,7 +411,7 @@ let pass_linearization_pre verbose debug =
               let neq_expr: t_expression = e in
               let vars = varlist_concat (t, [nvar]) vars in
               (neq_patt, neq_expr) :: eqs, vars, EMonOp (t, MOp_pre, EVar (t, nvar))
-          | _ ->
+          | _, _ ->
               let eqs, vars, e = pre_aux_expression vars e in
               eqs, vars, EMonOp (t, op, e)
           end
diff --git a/src/test.node b/src/test.node
index 6dd535f..d6f531d 100644
--- a/src/test.node
+++ b/src/test.node
@@ -1,10 +1,15 @@
+node id (a: bool) returns (o: bool);
+let
+  o = a;
+tel
+
 node test_merge_tuples (a, b: bool) returns (o: bool);
 var t: bool;
 let
   (o, t) = if a and b then (true, false) else (false, true);
 tel
 
---node my_and (a, b: bool) returns (o: bool);
---let
---  o = if a then b else false;
---tel
+node my_and (a, b: bool) returns (o: bool);
+let
+  o = if a then b else id(false -> a);
+tel