diff --git a/src/ast.ml b/src/ast.ml
index e61114c..af0ba62 100644
--- a/src/ast.ml
+++ b/src/ast.ml
@@ -1,53 +1,65 @@
-type ident = string
-
 type location = Lexing.position * Lexing.position
 
-type const =
-  | CBool of bool
-  | CInt of int
+type ident = string
+
+type real = float
+
+type _ const =
+  | CReal: real -> real const
+  | CBool: bool -> bool const
+  | CInt:  int  -> int const
 
 type monop =
-  | MOp_not
-  | MOp_minus
+  | MOp_not | MOp_minus | MOp_pre
 
 type binop =
   | BOp_add | BOp_sub | BOp_mul | BOp_div | BOp_mod
-  | BOp_and | BOp_or | BOp_eq | BOp_neq
+  | BOp_and | BOp_or | BOp_when
+
+type compop =
+  | BOp_eq | BOp_neq
   | BOp_le | BOp_lt | BOp_ge | BOp_gt
 
 type triop =
-  | TOp_if
+  | TOp_if | TOp_merge
+
+type _ t_var =
+  | BVar: ident -> bool t_var
+  | IVar: ident -> int t_var
+  | RVar: ident -> real t_var
+
+type _ t_expression =
+  | EVar: 'a t_var -> 'a t_expression
+  | EMonOp: monop * 'a t_expression -> 'a t_expression
+  | EBinOp: binop * 'a t_expression * 'a t_expression -> 'a t_expression
+  | ETriOp: triop * bool t_expression * 'a t_expression * 'a t_expression -> 'a t_expression
+  | EComp:  compop * 'a t_expression * 'a t_expression -> bool t_expression
+  | EConst: 'a const -> 'a t_expression
+  | ETuple: 'a t_expression * 'b t_expression -> ('a * 'b) t_expression
+  | EApp: (('a -> 'b) t_node) * 'a t_expression -> 'b t_expression
+
+and _ t_varlist =
+  | NVar: 'a t_varlist
+  | CVar: 'a t_var * 'b t_varlist -> ('a * 'b) t_varlist
+
+and 'a t_equation = 'a t_varlist * 'a t_expression
+
+and _ t_eqlist =
+  | NEql: unit t_eqlist
+  | CEql: 'a t_equation * 'b t_eqlist -> ('a * 'b) t_eqlist
+
+and _ t_node =
+  | MakeNode:
+    ident
+    * 'i t_varlist * 'o t_varlist
+    * 'l t_varlist * 'e t_eqlist
+    -> ('i -> 'o) t_node
+
+type _ t_nodelist =
+  | NNode: unit t_nodelist
+  | CNode: ('a -> 'b) t_node * 'c t_nodelist -> (('a -> 'b) * 'c) t_nodelist
 
 type base_ty =
-  | Tbool
-  | Tint
-
-type p_pattern =
-  | PP_var of ident
-  | PP_tuple of ident list
-
-type p_expression =
-  | PE_Const of const
-  | PE_Var of ident
-  | PE_MonOp of monop * p_expression
-  | PE_BinOp of binop * p_expression * p_expression
-  | PE_TriOp of triop * p_expression * p_expression * p_expression
-  | PE_app of ident * p_expression list
-  | PE_tuple of p_expression list
-  | PE_pre of p_expression
-  | PE_arrow of p_expression * p_expression
-
-type p_equation =
-  { peq_patt: p_pattern;
-    peq_expr: p_expression }
-
-type p_node =
-  { pn_name:       ident;
-    pn_input:      (ident * base_ty) list;
-    pn_output:     (ident * base_ty) list;
-    pn_local_vars: (ident* base_ty) list;
-    pn_equations:  p_equation list;
-    pn_loc:        location; }
-
-type p_prog = p_node list
-
+  | TBool
+  | TInt
+  | TReal