diff --git a/errors.ml b/errors.ml
new file mode 100644
index 0000000..ac8923e
--- /dev/null
+++ b/errors.ml
@@ -0,0 +1,42 @@
+open Ast
+open Lexing
+
+exception LexerError of char
+exception SemanticsError of string * Lexing.position
+
+let err msg pos =
+  Printf.eprintf
+    "Error on line %d col %d: %s.\n"
+    pos.pos_lnum
+    (pos.pos_cnum - pos.pos_bol)
+    msg;
+  exit 1
+;;
+
+let errt expected given pos =
+  let rec string_of_type_t = function
+    | Int_t -> "int"
+    | Bool_t -> "bool"
+    | Func_t (r, a) ->
+      (if List.length a > 1 then "(" else "")
+      ^ String.concat ", " (List.map string_of_type_t a)
+      ^ (if List.length a > 1 then ")" else "")
+      ^ " -> "
+      ^ string_of_type_t r
+  in
+  raise
+    (SemanticsError
+       ( Printf.sprintf
+           "Expected %s but given %s"
+           (string_of_type_t expected)
+           (string_of_type_t given)
+       , pos ))
+;;
+
+let warn msg (pos : Lexing.position) =
+  Printf.eprintf
+    "Warning on line %d col %d: %s.\n"
+    pos.pos_lnum
+    (pos.pos_cnum - pos.pos_bol)
+    msg
+;;
diff --git a/lexer.mll b/lexer.mll
index 514561a..b8bbdc7 100644
--- a/lexer.mll
+++ b/lexer.mll
@@ -1,8 +1,7 @@
 {
+  open Errors
   open Lexing
   open Parser
-
-  exception Error of char
 }
 
 let alpha = ['a'-'z' 'A'-'Z']
@@ -27,7 +26,7 @@ rule token = parse
 | '/'           { Ldiv }
 | ident as i    { Lvar i }
 | '#'           { comment lexbuf }
-| _ as c        { raise (Error c) }
+| _ as c        { raise (LexerError c) }
 
 and comment = parse
 | eof  { Lend }
diff --git a/main.ml b/main.ml
index f2cc502..a1a4d10 100644
--- a/main.ml
+++ b/main.ml
@@ -1,14 +1,4 @@
-open Lexing
-open Ast
-
-let err msg pos =
-  Printf.eprintf
-    "Error on line %d col %d: %s.\n"
-    pos.pos_lnum
-    (pos.pos_cnum - pos.pos_bol)
-    msg;
-  exit 1
-;;
+open Errors
 
 let () =
   if Array.length Sys.argv != 2
@@ -25,8 +15,8 @@ let () =
     let asm = Compiler.compile ast in
     Mips.emit Stdlib.stdout asm
   with
-  | Lexer.Error c ->
+  | LexerError c ->
     err (Printf.sprintf "Unrecognized char \"%c\"" c) (Lexing.lexeme_start_p buf)
   | Parser.Error -> err "Syntax error" (Lexing.lexeme_start_p buf)
-  | Semantics.Error (msg, pos) -> err msg pos
+  | SemanticsError (msg, pos) -> err msg pos
 ;;
diff --git a/semantics.ml b/semantics.ml
index 4f3ac54..d9d87e6 100644
--- a/semantics.ml
+++ b/semantics.ml
@@ -1,40 +1,7 @@
 open Ast
 open Ast.IR
 open Baselib
-
-(* Erreurs *)
-
-exception Error of string * Lexing.position
-
-let errt expected given pos =
-  let rec string_of_type_t = function
-    | Int_t -> "int"
-    | Bool_t -> "bool"
-    | Func_t (r, a) ->
-      (if List.length a > 1 then "(" else "")
-      ^ String.concat ", " (List.map string_of_type_t a)
-      ^ (if List.length a > 1 then ")" else "")
-      ^ " -> "
-      ^ string_of_type_t r
-  in
-  raise
-    (Error
-       ( Printf.sprintf
-           "Expected %s but given %s"
-           (string_of_type_t expected)
-           (string_of_type_t given)
-       , pos ))
-;;
-
-let warn msg (pos : Lexing.position) =
-  Printf.eprintf
-    "Warning on line %d col %d: %s.\n"
-    pos.pos_lnum
-    (pos.pos_cnum - pos.pos_bol)
-    msg
-;;
-
-(* Sémantique *)
+open Errors
 
 let analyze_value = function
   | Syntax.Int n -> Int n, Int_t
@@ -48,7 +15,7 @@ let rec analyze_expr env ua t = function
     Val v2, new_t
   | Syntax.Var v ->
     if not (Env.mem v.name env)
-    then raise (Error ("Unbound variable \"" ^ v.name ^ "\"", v.pos));
+    then raise (SemanticsError ("Unbound variable \"" ^ v.name ^ "\"", v.pos));
     if List.mem v.name ua then warn ("Unassigned variable \"" ^ v.name ^ "\"") v.pos;
     let new_t = Env.find v.name env in
     if new_t != t then errt t new_t v.pos;
@@ -75,14 +42,14 @@ let rec analyze_expr env ua t = function
               tl
               c.args )
       , ret_t )
-    | _ -> raise (Error ("\"" ^ c.func ^ "\" isn't a function", c.pos)))
+    | _ -> raise (SemanticsError ("\"" ^ c.func ^ "\" isn't a function", c.pos)))
 ;;
 
 let analyze_instr env ua = function
   | Syntax.Decl d -> Decl d.name, Env.add d.name d.type_t env, [ d.name ] @ ua
   | Syntax.Assign a ->
     if not (Env.mem a.var env)
-    then raise (Error ("Unbound variable \"" ^ a.var ^ "\"", a.pos));
+    then raise (SemanticsError ("Unbound variable \"" ^ a.var ^ "\"", a.pos));
     let ae, et = analyze_expr env ua (Env.find a.var env) a.expr in
     Assign (a.var, ae), env, List.filter (fun x -> x <> a.var) ua
   | Syntax.Return r ->