diff --git a/.gitignore b/.gitignore
index b430460..81c81cb 100644
--- a/.gitignore
+++ b/.gitignore
@@ -11,6 +11,7 @@
 # example
 /examples/pydump
 /examples/pypp
+/examples/pysimpl
 
 # src
 /src/lexer.ml
diff --git a/examples/Makefile b/examples/Makefile
index 6772d74..44f3d23 100644
--- a/examples/Makefile
+++ b/examples/Makefile
@@ -1,4 +1,4 @@
-all: pydump pypp
+all: pydump pypp pysimpl
 
 pydump: pydump.ml
 	ocamlfind ocamlopt -o pydump -linkpkg -package pythonlib pydump.ml
@@ -6,5 +6,8 @@ pydump: pydump.ml
 pypp: pypp.ml
 	ocamlfind ocamlopt -o pypp -linkpkg -package pythonlib pypp.ml
 
+pysimpl: pysimpl.ml
+	ocamlfind ocamlopt -o pysimpl -linkpkg -package pythonlib pysimpl.ml
+
 clean:
-	rm -f pydump pypp *.cm[ixo] *.o
+	rm -f pydump pypp pysimpl *.cm[ixo] *.o
diff --git a/examples/pysimpl.ml b/examples/pysimpl.ml
new file mode 100644
index 0000000..fc86219
--- /dev/null
+++ b/examples/pysimpl.ml
@@ -0,0 +1,82 @@
+open Pythonlib.Simpl
+open Pythonlib.Ast
+
+let tmp_prefix = "__"
+
+let is_tmpid =
+  let len = String.length tmp_prefix in
+  fun x ->
+    let l = String.length x in
+    let rec d i =
+      if i>=l then true
+      else
+        if i>=len then
+          (match x.[i] with
+          | '0'..'9' -> d (i+1)
+          | _ -> false)
+        else
+          (x.[i] = tmp_prefix.[i]) && d (i+1) in
+    d 0
+
+let list_count f =
+  let rec c n = function
+    | [] -> n
+    | hd :: tl -> c (if f hd then n+1 else n) tl
+  in
+  c 0
+
+let preferred a b =
+  let f x =
+    match x with
+    | Name(x, Param, _) -> is_tmpid x
+    | _ -> assert false in
+  let fst (x, _, _, _) = x in
+  let score_a = list_count f (fst a) in
+  let score_b = list_count f (fst b) in
+  if score_a > score_b then b else a
+
+let same_args formal effective kw star kwargs =
+  kw=[]
+  && star=None
+    && kwargs=None
+      && match formal with
+      | (formal, None, None, []) ->
+        let is_in n =
+          let rec loop l =
+            match l with
+            | [] -> false
+            | Name(m, _, _) :: tl -> n=m || loop tl
+            | _ :: tl -> loop tl in
+          loop in
+        let rec s f e =
+          match f with
+          | [] -> e=[]
+          | Name(n, Param, _) :: tlf when not(is_in n tlf) ->
+            (match e with
+            | Name(n', Load, _) :: tle when n=n' -> s tlf tle
+            | _ -> false)
+          | _ -> false in
+        s formal effective
+      | _ -> false
+
+let se = function
+  | Lambda(args,
+           Call(Lambda(args', body', al'), eargs, kw, star, kwargs, ac), al)
+      when same_args args eargs kw star kwargs
+        -> Some (Lambda(preferred args args', body', al'))
+  | _ -> None
+
+let ss = function
+  | FunctionDef(id, args,
+                [Return(Some(Call(Lambda(args', body', al), eargs, kw, star, kwargs, ac)), ar)], deco, af)
+      when same_args args eargs kw star kwargs
+        -> Some (FunctionDef(id, preferred args args',
+                             [Return(Some(body'), ar)], deco, af))
+  | _ -> None
+
+let s = {
+  simpl_expr = Some se;
+  simpl_stmt = Some ss }
+
+let () =
+  Pythonlib.Pretty.print_mod (simpl s (Pythonlib.Parser2.parse_from_channel stdin))
diff --git a/src/OMakefile b/src/OMakefile
index 01b4bc2..0ca04c2 100644
--- a/src/OMakefile
+++ b/src/OMakefile
@@ -4,7 +4,7 @@ BYTE_ENABLED = true
 NATIVE_ENABLED = true
 USE_OCAMLFIND = true
 
-FILES[] = utils ast token lexer lexer_state python2_parser parser2 pretty dump
+FILES[] = utils ast token lexer lexer_state python2_parser parser2 pretty dump simpl
 PACK = $(OCamlPackage $(LIBRARY), $(FILES))
 LIB = $(OCamlLibrary $(LIBRARY), $(rootname $(PACK)))
 OCAMLYACC = ../build-aux/ocamlyacc
diff --git a/src/pretty.ml b/src/pretty.ml
index bb29758..28f0f17 100644
--- a/src/pretty.ml
+++ b/src/pretty.ml
@@ -270,7 +270,11 @@ and pp_expr fmt = function
 
   | Call (func, args, keywords, starargs, kwargs, _) ->
       let comma = mk_sep ", " in
-        fprintf fmt "%a(" pp_expr func;
+      let paren =
+        match func with
+        | Name _ | Call _ | Attribute _ | Subscript _ -> false
+        | _ -> true in
+        if paren then fprintf fmt "(%a)(" pp_expr func else fprintf fmt "%a(" pp_expr func;
         List.iter (fprintf fmt "%t%a" comma pp_expr) args;
         List.iter
           (fun (arg, value) ->
@@ -307,6 +311,9 @@ and pp_expr fmt = function
   | List (elts, _, _) ->
       fprintf fmt "[@[%a@]]" pp_expr_list elts
 
+  | Tuple ([elt], _, _) ->
+    fprintf fmt "(%a,)" pp_expr elt
+
   | Tuple (elts, _, _) ->
       pp_paren_expr_list fmt elts
 
diff --git a/src/simpl.ml b/src/simpl.ml
new file mode 100644
index 0000000..0ee87f2
--- /dev/null
+++ b/src/simpl.ml
@@ -0,0 +1,96 @@
+open Ast
+
+exception Empty_statement_list
+
+type 'a simplifier = {
+  simpl_expr: ('a expr -> 'a expr option) option;
+  simpl_stmt: ('a stmt -> 'a stmt option) option }
+
+let simpl s =
+  let sexpr =
+    match s.simpl_expr with
+    | None -> (fun _ -> None)
+    | Some s -> s in
+  let sstmt =
+    match s.simpl_stmt with
+    | None -> (fun _ -> None)
+    | Some s -> s in
+  let rec _expr e =
+    let e' =
+      (match e with
+      | BoolOp(op, vals, ab) -> BoolOp(op, List.map _expr vals, ab)
+      | BinOp(left, op, right, ab) -> BinOp(_expr left, op, _expr right, ab)
+      | UnaryOp(op, operand, au) -> UnaryOp(op, _expr operand, au)
+      | Lambda(args, body, al) -> Lambda(args, body, al)
+      | IfExp(test, body, orelse, ai) -> IfExp(_expr test, _expr body, _expr orelse, ai)
+      | Dict(keys, vals, ad) -> Dict(List.map _expr keys, List.map _expr vals, ad)
+      | ListComp(elt, generators, al) -> ListComp(_expr elt, List.map _compr generators, al)
+      | GeneratorExp(elt, generators, ag) -> GeneratorExp(_expr elt, List.map _compr generators, ag)
+      | Yield(vals, ay) -> Yield(_optexpr vals, ay)
+      | Compare(left, ops, right, ac) -> Compare(_expr left, ops, List.map _expr right, ac)
+      | Call(func, args, keywords, star, kwarg, ac) -> Call(_expr func, List.map _expr args, List.map _keyword keywords, _optexpr star, _optexpr kwarg, ac)
+      | Repr(vals, ar) -> Repr(_expr vals, ar)
+      | Num _ | Str _ | Name _ -> e
+      | Attribute(vals, attr, ctx, aa) -> Attribute(_expr vals, attr, ctx, aa)
+      | Subscript(vals, slice, ctx, a) -> Subscript(_expr vals, _slice slice, ctx, a)
+      | List(elts, ctx, al) -> List(List.map _expr elts, ctx, al)
+      | Tuple(elts, ctx, at) -> Tuple(List.map _expr elts, ctx, at)) in
+    match sexpr e' with
+    | None -> e'
+    | Some e'' -> _expr e''
+  and _optexpr e =
+    match e with
+    | None -> e
+    | Some e -> Some(_expr e)
+  and _keyword (arg, vals) = (arg, _expr vals)
+  and _slice s =
+    match s with
+    | Ellipsis -> s
+    | Slice(lower, upper, step) -> Slice(_optexpr lower, _optexpr upper, _optexpr step)
+    | ExtSlice(dims) -> ExtSlice(List.map _slice dims)
+    | Index(vals) -> Index(_expr vals)
+  and _compr (target, iter, ifs) = (_expr target, _expr iter, List.map _expr ifs) in
+  let rec _stmt s =
+    let s' =
+      (match s with
+      | FunctionDef(id, args, body, deco, af) -> FunctionDef(id, args, _stmt_list body, List.map _expr deco, af)
+      | ClassDef(id, bases, body, deco, ac) -> ClassDef(id, List.map _expr bases, _stmt_list body, List.map _expr deco, ac)
+      | Return(r, ar) -> Return(_optexpr r, ar)
+      | Delete(e, ad) -> Delete(List.map _expr e, ad)
+      | Assign(targets, vals, aa) -> Assign(List.map _expr targets, _expr vals, aa)
+      | AugAssign(target, op, vals, aa) -> AugAssign(_expr target, op, _expr vals, aa)
+      | Print(dest, vals, nl, ap) -> Print(_optexpr dest, List.map _expr vals, nl, ap)
+      | For(target, iter, body, orelse, af) -> For(_expr target, _expr iter, _stmt_list body, List.map _stmt orelse, af)
+      | While(test, body, orelse, aw) -> While(_expr test, _stmt_list body, List.map _stmt orelse, aw)
+      | If(test, body, orelse, ai) -> If(_expr test, _stmt_list body, _stmt_list orelse, ai)
+      | With(ctx, vars, body, aw) -> With(_expr ctx, _optexpr vars, _stmt_list body, aw)
+      | Raise(typ, inst, tback, ar) -> Raise(_optexpr typ, _optexpr inst, _optexpr tback, ar)
+      | TryExcept(body, handlers, orelse, at) -> TryExcept(_stmt_list body, List.map _handler handlers, List.map _stmt orelse, at)
+      | TryFinally(body, final, at) -> TryFinally(_stmt_list body, List.map _stmt final, at)
+      | Assert(test, msg, aa) -> Assert(_expr test, _optexpr msg, aa)
+      | Import _ | ImportFrom _ | Global _ | Pass _ | Break _ | Continue _ -> s
+      | Exec(body, globals, locals, ae) -> Exec(_expr body, _optexpr globals, _optexpr locals, ae)
+      | Expr(v, ae) -> Expr(_expr v, ae)) in
+    match sstmt s' with
+    | None -> s'
+    | Some s'' -> _stmt s''
+  and _handler h =
+    match h with
+    | ExceptHandler(typ, name, body, ae) -> ExceptHandler(_optexpr typ, _optexpr name, List.map _stmt body, ae)
+  and _stmt_list l =
+    let rec loop l =
+      match l with
+      | [] -> []
+      | ((Return _ | Raise _ | Pass _ | Break _ | Continue _) as s) :: _ -> [_stmt s]
+      | s :: tl -> _stmt s :: _stmt_list l
+    in
+    match l with
+    | [] -> raise Empty_statement_list
+    | _ -> loop l in
+
+  fun m ->
+    match m with
+    | Module(l, am) -> Module(List.map _stmt l, am)
+    | Interactive(l, ai) -> Interactive(List.map _stmt l, ai)
+    | Expression(e, ae) -> Expression(_expr e, ae)
+    | Suite(l, a) -> Suite(List.map _stmt l, a)