diff --git a/assemble.ml b/assemble.ml
index 6abf7b7..f155d56 100644
--- a/assemble.ml
+++ b/assemble.ml
@@ -96,6 +96,8 @@ let sc2lua (name, arity, body) =
     name ^ "_combinator = { F, " ^ name ^ ", " ^ show arity ^ ", " ^ show name ^ " };"
   body ^ "\n" ^ dec
 
+let private pasted_files : ref (S.t string) = ref S.empty
+
 let foreign2lua (Fimport { cc, fent = fspec, var, ftype }) =
   let (file, fspec) =
     match Strings.split_on " " fspec with
@@ -123,12 +125,16 @@ let foreign2lua (Fimport { cc, fent = fspec, var, ftype }) =
     let contents =
       match file with
       | Some path -> 
-        let f = open_for_reading path
-        let x = read_all f
-        close_file f
-        match x with
-        | Some s -> "--- " ^ path ^ "\n" ^ s ^ "\n"
-        | None -> ""
+          if path `S.member` !pasted_files then
+            ""
+          else
+            pasted_files := S.insert path !pasted_files
+            let f = open_for_reading path
+            let x = read_all f
+            close_file f
+            match x with
+            | Some s -> "--- " ^ path ^ "\n" ^ s ^ "\n"
+            | None -> ""
       | None -> ""
     contents ^ wrapper ^ "\n" ^ dec
 
@@ -153,4 +159,4 @@ let assm_program decs =
     let local_decs =
       foldl (fun x v -> x ^ ", " ^ v) ("local " ^ local1) locals
     let body = foldl (fun x s -> x ^ codegen s ^ "\n") "" decs
-    preamble ^ local_decs ^ "\n" ^ body ^ "unwind({{ A, main_combinator, 123 }}, 1)"
+    preamble ^ local_decs ^ "\n" ^ body ^ "unwind({main_combinator}, 1)"
diff --git a/compile.ml b/compile.ml
index 977f2c2..d4117a5 100644
--- a/compile.ml
+++ b/compile.ml
@@ -89,8 +89,8 @@ let rec lambda_lift strict = function
           |> free_vars
           |> flip S.difference known_sc
           |> S.members
-      let def = ("Lam" ^ show i, vars, case)
-      let app = foldl (fun f -> app f # Ref) (Ref ("Lam" ^ show i)) vars
+      let def = ("Case" ^ show i, vars, case)
+      let app = foldl (fun f -> app f # Ref) (Ref ("Case" ^ show i)) vars
       put (i + 1, Decl def :: defs, known_sc)
         |> map (const app)
   | Let (vs, e) ->
diff --git a/driver.ml b/driver.ml
index 3adbc06..1141ae9 100644
--- a/driver.ml
+++ b/driver.ml
@@ -5,6 +5,9 @@ open import "./parser.ml"
 open import "prelude.ml"
 open import "lua/io.ml"
 
+module Stg = import "./stg/lower.ml"
+module Out = import "./stg/output.ml"
+
 external val dofile : string -> () = "dofile"
 
 let printerror (e, { line, col }) =
@@ -53,6 +56,35 @@ let test_file infile =
   | None -> ()
   close_file infile
 
+let rec take n xs =
+  match n, xs with
+  | _, [] -> []
+  | 0, _ -> []
+  | n, Cons (x, xs) -> Cons (x, take (n - 1) xs)
+
+let go_stg infile outfile =
+  let infile = open_for_reading infile
+  let outfile = open_file outfile Write_m
+  match read_all infile with
+  | Some str -> 
+    match lex prog str with
+    | Right (ds, _) ->
+      let decs =
+        ds |> T.tc_program [] []
+          |> fun (_, _, z) -> z
+          |> flip (>>=) Stg.lower_dec
+      let (_, sts, locals) = foldl Out.stmts_of_def (M.empty, [], []) decs
+      write_bytes outfile "local Constr_mt = { __call = function(x) return x end }\n"
+      Out.get_file_contents () |> (^"\n") |> write_bytes outfile
+      write_bytes outfile (Out.mk_pap_def ^ "\n")
+      write_bytes outfile (Out.ppr_stmt "" (Out.Local (take 100 locals, [])) ^ "\n")
+      iter (write_bytes outfile # (^"\n") # Out.ppr_stmt "") sts
+      write_bytes outfile "main_entry(function() return 'the real world is fake' end)\n"
+    | Left e ->
+      printerror e
+  | None -> ()
+  close_file infile
+  close_file outfile
 
 external val args : string * string =
   "{ _1 = select(1, ...), _2 = select(2, ...) }"
diff --git a/lib/parsers.ml b/lib/parsers.ml
index dea9f4a..929c57e 100644
--- a/lib/parsers.ml
+++ b/lib/parsers.ml
@@ -234,7 +234,7 @@ let chainr1 p op =
       pure (f x y)
     ) <|> pure x
   let _ = rest (* shut up, amc *)
-  scan
+  force scan
 
 let parse (P x) s =
   let! x = x { line = 0, col = 0 } s
@@ -254,5 +254,5 @@ let lift m = P @@ fun pos s ->
   let! x = m
   pure @@ Ok (E, x, s, pos)
 
-let morph (k : forall 'a. 'm 'a -> 'n 'a) (P x) = P @@ fun s -> k (x s)
+let morph (k : forall 'a. 'm 'a -> 'n 'a) (P x) = P @@ fun p s -> k (x p s)
 let void x = map (const ()) x
diff --git a/stg/lower.ml b/stg/lower.ml
new file mode 100644
index 0000000..b9b4539
--- /dev/null
+++ b/stg/lower.ml
@@ -0,0 +1,186 @@
+open import "prelude.ml"
+module Src = import "../lang.ml"
+open Src
+
+module Map = import "data/map.ml"
+module Set = import "data/set.ml"
+module Stg = import "./stg.ml"
+
+let spine f =
+  let rec spine = function
+    | App (f, x) ->
+      let (f, args) = spine f
+      (f, x :: args)
+    | e -> (e, [])
+  let (f, args) = spine f
+  (f, reverse args)
+
+let rec napp f = function
+  | [] -> f
+  | Cons (x, xs) -> napp (App (f, x)) xs
+
+let get_con_arities prog =
+  let go_con m (Constr (name, tys)) = M.insert name (length tys) m
+  let go m = function
+    | Data (_, _, cons) -> foldl go_con m cons
+    | _ -> m
+  foldl go M.empty prog
+
+let gensym =
+  let counter = ref 0
+  fun () ->
+    counter := !counter + 1
+    "_s" ^ show !counter
+
+let rec add_n_args da exp =
+  if da <= 0 then
+    exp
+  else
+    let var = gensym ()
+    Lam (var, App (add_n_args (da - 1) exp, Ref var))
+
+let rec eta_expand_cons arities =
+  let rec go = function
+    | Case (exp, alts) -> Case (go exp, map (second (second go)) alts)
+    | Lam (var, alts) -> Lam (var, go alts)
+    | If (a, b, c) -> If (go a, go b, go c)
+    | Let (decs, body) -> Let (map (second go) decs, go body)
+    | exp ->
+      match spine exp with
+      | Ref func, args ->
+        let arg_len = length args
+        match Map.lookup func arities with
+        | Some arity when arity > arg_len -> add_n_args (arity - arg_len) (napp (Ref func) args)
+        | _ -> exp
+      | _, _ -> error @@ "What?"
+  go
+
+let build_stg_app func = function
+  | [] -> Stg.Atom func
+  | args -> Stg.(App (func, args))
+
+let mk_lambda_form name exp =
+  let free_vars = Stg.stg_fv exp
+  { name, free_vars, update = Stg.Updatable, args = [], body = exp }
+
+let mk_function name args exp =
+  let free_vars = foldl (flip Set.delete) (Stg.stg_fv exp) args
+  { name, free_vars, update = Stg.Function, args, body = exp }
+
+let rec unlambda = function
+  | Lam (var, body) ->
+    let (args, body) = unlambda body
+    (var :: args, body)
+  | e -> ([], e)
+
+let rec lower_spine (func, args) kont =
+  lower_atom func @@ fun func ->
+    let rec go kont lowered = function
+      | [] -> kont (build_stg_app func (reverse lowered))
+      | Cons (Ref e, args) ->
+        go kont (Stg.Var e :: lowered) args
+      | Cons (Lit i, args) ->
+        go kont (Stg.Int i :: lowered) args
+      | Cons (arg, args) ->
+        lower_atom arg @@ fun arg ->
+          go kont (arg :: lowered) args
+    go kont [] args
+and lower exp kont =
+  match spine exp with
+  | exp, [] ->
+    match exp with
+    | App _ -> error @@ "Impossible lower App with empty spine"
+    
+    (* STG atoms *)
+    | Ref e -> kont Stg.(Atom (Var e))
+    | Lit e -> kont Stg.(Con (0, 1, [Int e]))
+
+    (* Lambdas need to be bound as lambda-forms *)
+    | Lam _ as lam ->
+      let name = gensym ()
+      let (args, body) = unlambda lam
+      let body = lower_body body
+      Stg.Let ([mk_function name args body], kont Stg.(Atom (Var name)))
+
+    | If (cond, th, el) ->
+      lower cond @@ fun cond ->
+        lower th @@ fun th ->
+          lower el @@ fun el ->
+            Stg.( Case (cond, "binder" ^ gensym(), [(Con_pat (0, []), th), (Default, el)]) )
+              |> kont
+
+    | Let (bindings, body) ->
+      lower_binds bindings @@ fun lambda_forms ->
+        Stg.Let (lambda_forms, lower body kont)
+    
+    | Case (scrut, arms) ->
+      lower scrut @@ fun scrut ->
+        lower_arms arms @@ fun arms ->
+          Stg.Case (scrut, "binder" ^ gensym(), arms) |> kont
+  | e -> lower_spine e kont
+
+and lower_atom exp kont =
+  lower exp @@ function
+    | Stg.Atom at -> kont at
+    | e ->
+      let name = gensym ()
+      Stg.(Let ([mk_lambda_form name e], kont (Var name)))
+
+and lower_binds bindings kont =
+  let rec go acc = function
+    | [] -> kont (reverse acc)
+    | Cons ((name, bind), rest) ->
+      go (lower_rhs name bind :: acc) rest
+  go [] bindings
+
+and lower_arms arms kont =
+  let rec go i acc = function
+    | [] -> kont (reverse acc)
+    | Cons ((_, args, exp), rest) ->
+      let body = lower_body exp
+      go (i + 1) ((Stg.(Con_pat (i, args)), body) :: acc) rest
+  go 0 [] arms
+
+and lower_rhs name exp =
+  match exp with
+  | Lam _ as lam -> 
+    let (args, body) = unlambda lam
+    let body = lower_body body
+    mk_function name args body
+  | _ ->
+    let body = lower_body exp
+    mk_lambda_form name body
+
+and lower_body exp = lower exp (fun x -> x)
+
+let mk_stg_prim name prim =
+  let binary_prim x =
+    let open Stg
+    let body =
+      Case (Atom (Var "x"), "x",
+        [( Default, Case (Atom (Var "y"), "y",
+          [(Default, Prim (x, [Var "x", Var "y"]))]))])
+    Fun { name, args = ["x", "y"], body, is_con = None }
+  match prim with
+  | "add" -> binary_prim Stg.Add
+  | "sub" -> binary_prim Stg.Sub
+  | "mul" -> binary_prim Stg.Mul
+  | "div" -> binary_prim Stg.Div
+  | "equ" -> binary_prim Stg.Equ
+  | e -> error @@ "No such primitive " ^ e
+
+let lower_dec = function
+  | Decl (name, manifest_args, expr) ->
+    let (args, body) = unlambda expr
+    let args = manifest_args ++ args
+    let body = lower_body body
+    [ Stg.Fun { name, args, body, is_con = None } ]
+  | Data (_, _, cons) ->
+    let mk_stg_con (Constr (name, args), i) =
+      let args = [ gensym () | with _ <- args ]
+      Stg.Fun { name, args, body = build_stg_app (Stg.Var name) (Stg.Var <$> args), is_con = Some i }
+    [ mk_stg_con c | with c <- zip cons [0 .. length cons - 1] ]
+  | Foreign (Fimport { cc = Prim, fent = prim, var = name }) ->
+    [ mk_stg_prim name prim ]
+  | Foreign (Fimport { cc = Lua, fent, var, ftype }) ->
+    [ Stg.Ffi_def { name = var, fent, arity = arity ftype }]
\ No newline at end of file
diff --git a/stg/output.ml b/stg/output.ml
new file mode 100644
index 0000000..8b3d870
--- /dev/null
+++ b/stg/output.ml
@@ -0,0 +1,270 @@
+module Stg = import "./stg.ml"
+module Map = import "data/map.ml"
+module Set = import "data/set.ml"
+module Strings = import "../lib/strings.ml"
+
+open Stg
+
+open import "lua/io.ml"
+open import "prelude.ml"
+
+type lua_ref 'expr =
+  | Lvar   of string
+  | Lindex of lua_ref 'expr * 'expr
+
+type lua_expr 'stmt =
+  | Lfunc   of list string * list 'stmt
+  | Lcall_e of lua_expr 'stmt * list (lua_expr 'stmt)
+  | Lstr    of string
+  | Lint    of int
+  | Lref    of lua_ref (lua_expr 'stmt)
+  | Lbop    of lua_expr 'stmt * string * lua_expr 'stmt
+  | Ltable  of list (lua_expr 'stmt * lua_expr 'stmt)
+  | Ltrue
+  | Ldots
+
+type lua_stmt =
+  | Return of lua_expr lua_stmt
+  | Local  of list string * list (lua_expr lua_stmt)
+  | Func   of string * list string * list lua_stmt
+  | Assign of list (lua_ref (lua_expr lua_stmt)) * list (lua_expr lua_stmt)
+  | If     of lua_expr lua_stmt * list lua_stmt * list lua_stmt
+
+let rec ppr_ref indl = function
+  | Lvar v -> v
+  | Lindex (e, Lstr x) -> ppr_ref indl e ^ "." ^ x
+  | Lindex (e, e') -> ppr_ref indl e ^ "[" ^ ppr_expr indl e' ^ "]"
+
+and ppr_expr indl = function
+  | Lfunc (args, body) ->
+    "function(" ^ ppr_args args ^ ")\n" ^ ppr_body (indl ^ "  ") body ^ indl ^ "end"
+  | Lcall_e (Lref _ as func, args) ->
+    ppr_expr indl func ^ "(" ^ ppr_args (ppr_expr indl <$> args) ^ ")"
+  | Lcall_e (func, args) ->
+    "(" ^ ppr_expr indl func ^ ")(" ^ ppr_args (ppr_expr indl <$> args) ^ ")"
+  | Lstr s -> show s
+  | Lint i -> show i
+  | Ldots -> "..."
+  | Lref r -> ppr_ref indl r
+  | Ltrue -> "true"
+  | Lbop (l, o, r) -> ppr_expr indl l ^ " " ^ o ^ " " ^ ppr_expr indl r
+  | Ltable entries -> "{" ^ ppr_args (ppr_pair indl <$> entries) ^ "}"
+
+and ppr_stmt indl = function
+  | Return r -> "return " ^ ppr_expr indl r
+
+  | If (c, t, []) ->
+    "if " ^ ppr_expr indl c ^ " then\n"
+      ^ ppr_body (indl ^ "  ") t
+      ^ indl ^ "end"
+
+  | If (c, [], e) ->
+    "if not (" ^ ppr_expr indl c ^ ") then\n"
+      ^ ppr_body (indl ^ "  ") e
+      ^ indl ^ "end"
+
+  | If (c, t, e) ->
+    "if " ^ ppr_expr indl c ^ " then\n"
+      ^ ppr_body (indl ^ "  ") t
+      ^ indl ^ "else\n"
+      ^ ppr_body (indl ^ "  ") e
+      ^ indl ^ "end"
+  
+  | Local ([], []) -> ""
+  | Local (vs, []) -> "local " ^ ppr_args vs
+  | Local (vs, es) ->
+    "local " ^ ppr_args vs ^ " = " ^ ppr_args (ppr_expr indl <$> es)
+  | Assign (vs, es) ->
+    ppr_args (ppr_ref indl <$> vs) ^ " = " ^ ppr_args (ppr_expr indl <$> es)
+  | Func (n, args, body) ->
+    "function " ^ n ^ "(" ^ ppr_args args ^ ")\n" ^ ppr_body (indl ^ "  ") body ^ indl ^ "end"
+
+and ppr_args = function
+  | [] -> ""
+  | Cons (a, args) -> foldl (fun a b -> a ^ ", " ^ b) a args
+
+and ppr_body indl = function
+  | [] -> "\n"
+  | Cons (a, args) ->
+    foldl (fun a b -> a ^ "\n" ^ indl ^ b) (indl ^ ppr_stmt indl a) (ppr_stmt indl <$> args) ^ "\n"
+
+and ppr_pair indl (k, v) = "[" ^ ppr_expr indl k ^ "] = " ^ ppr_expr indl v
+
+let gensym =
+  let counter = ref 0
+  fun () ->
+    counter := !counter + 1
+    "_a" ^ show !counter
+
+let escape = function
+  | "nil" -> "_Lnil"
+  | x -> x
+
+let var x = Lref (Lvar (escape x))
+
+let mk_pap_def =
+  "\
+local function mk_pap(fun, ...) \
+  local pending = { ... }\
+  return setmetatable({}, { __call = function(...) \
+    local args = table.pack(...)\
+    for i = 1, #pending do\
+      table.insert(args, i, pending[i])\
+    end\
+    return fun(unpack(args, 1, args.n + #pending))\
+  end}) \
+end"
+
+let make_lambda name args body =
+  let name = escape name
+  let args = map escape args
+  let arity = length args
+  [ Local ([name, name ^ "_entry" ], []),
+    Func (name ^ "_entry", args, body),
+    Func (name, ["..."], [
+      If (Lbop (Lcall_e (var "select", [Lstr "#", Ldots]), "==", Lint arity), [
+        Return (Lcall_e (var (name ^ "_entry"), [Ldots]))
+      ], [
+        If (Lbop (Lcall_e (var "select", [Lstr "#", Ldots]), ">", Lint arity), [
+          Local (["_spill"], [Lcall_e (var "table.pack", [Ldots])]),
+          Return (Lcall_e (Lcall_e (var (name ^ "_entry"), [Ldots]),
+            [Lcall_e (var "table.unpack", [var "_spill", Lint arity, var "_spill.n"])]))
+        ], [
+          Return (Lcall_e (var "mk_pap", [var name, Ldots]))
+      ])])])]
+
+let expr_of_atom = function
+  | Var v -> var v
+  | Int i -> Lfunc ([], [Return (Lint i)])
+
+let return x = [Return x]
+
+let rec stmts_of_expr arities = function
+  | Atom _ as a  -> expr_of_expr arities a |> return
+  | App _ as a   -> expr_of_expr arities a |> return
+  | Prim (f, xs) -> stmts_of_prim (f, expr_of_atom <$> xs)
+  | Con _ as a   -> expr_of_expr arities a |> return
+  | Case (expr, binder, alts) ->
+    let rec make_cases = function
+      | [] -> [Return (Lcall_e (var "error", [Lstr "Unmatched case"]))]
+      | Cons ((Default, tail), _) -> stmts_of_expr arities tail
+      | Cons ((Con_pat (tag, names), tail), rest) ->
+        let accesses =
+          [ Lref (Lindex (Lvar binder, Lint (i + 1)))
+          | with i <- [1 .. length names]
+          ]
+        [If (Lbop (Lref (Lindex (Lvar binder, Lint 1)), "==", Lint tag),
+          Local (names, accesses) :: stmts_of_expr arities tail,
+          make_cases rest
+        )]
+    Local ([binder], [enter arities expr]) :: make_cases alts
+  | Let (binders, rest) ->
+    let names = map (.name) binders
+    Local (names, []) :: gen_lambda_forms arities binders ++ stmts_of_expr arities rest
+
+and expr_of_expr arities = function
+  | Atom (Var v) ->
+    match Map.lookup v arities with
+    | Some (Left (0, tag)) -> Lcall_e (var "setmetatable", [ Ltable [(Lint 1, Lint tag)], var "Constr_mt" ])
+    | _ -> expr_of_atom (Var v)
+  | Atom a -> expr_of_atom a
+
+  | App (f, xs)  ->
+    match f with
+    | Int _ -> error "Attempt to call int"
+    | Var v ->
+      match Map.lookup v arities with
+      | Some (Right x) when x == length xs ->
+        (Lcall_e (var (v ^ "_entry"), expr_of_atom <$> xs))
+      | Some (Left (x, tag)) when x == length xs ->
+        let go i a = (Lint (i + 1), expr_of_atom a)
+        Lcall_e (var "setmetatable", [
+          Ltable ((Lint 1, Lint tag) :: zip_with go [1..length xs] xs),
+          var "Constr_mt"
+        ])
+      | _ -> Lcall_e (var v, expr_of_atom <$> xs)
+
+  | Prim (f, xs) -> expr_of_prim (f, expr_of_atom <$> xs)
+
+  | Con (tag, _, atoms) ->
+      let go i a = (Lint (i + 1), expr_of_atom a)
+      Lcall_e (var "setmetatable", [
+        Ltable ((Lint 1, Lint tag) :: zip_with go [1..length atoms] atoms),
+        var "Constr_mt"
+      ])
+    
+  | e -> Lcall_e (Lfunc ([], stmts_of_expr arities e), [])
+
+and enter arities expr =
+  Lcall_e (expr_of_expr arities expr, [])
+
+and expr_of_prim = function
+  | Add, [a, b] -> Lfunc ([], [Return (Lbop (a, "+", b))])
+  | Sub, [a, b] -> Lfunc ([], [Return (Lbop (a, "-", b))])
+  | Mul, [a, b] -> Lfunc ([], [Return (Lbop (a, "*", b))])
+  | Div, [a, b] -> Lfunc ([], [Return (Lbop (a, "/", b))])
+  | e -> Lcall_e (Lfunc ([], stmts_of_prim e), [])
+
+and stmts_of_prim = function
+  | Equ, [a, b] -> [
+      If (Lbop (a, "==", b),
+        stmts_of_expr Map.empty (Con (0, 0, [])),
+        stmts_of_expr Map.empty (Con (1, 0, [])))
+    ]
+  | e -> expr_of_prim e |> return
+
+and gen_lambda_forms arities : list (lambda_form stg_expr) -> list lua_stmt = function
+  | [] -> []
+  | Cons ({update = Function, name, args, body}, rest) ->
+    let arities = Map.insert name (Right (length args)) arities
+    let bst = stmts_of_expr arities body
+    tail (make_lambda name args bst) ++ gen_lambda_forms arities rest
+  | Cons ({update = Updatable, name, args, body}, rest) ->
+    let body = expr_of_expr arities body
+    let s = Assign ([Lvar name], [
+      Lcall_e (var "setmetatable", [
+        Ltable [],
+        Ltable [ (Lstr "__call", Lfunc (["_self"], [
+          If (Lref (Lindex (Lvar "_self", Lint 1)), [
+            Return (Lref (Lindex (Lvar "_self", Lint 1)))
+          ], [
+            Local (["val"], [Lcall_e (body, [])]),
+            Assign ([Lindex (Lvar "_self", Lint 1)], [var "val"]),
+            Return (var "val")
+          ])
+        ]))
+        ]
+      ])
+    ])
+    s :: gen_lambda_forms arities rest
+
+let private pasted_files : ref (Set.t string) = ref Set.empty
+
+let stmts_of_def (arities, code, locals) = function
+  | Fun { name, args, body, is_con } ->
+    let arities = Map.insert name (match is_con with | Some i -> Left (length args, i) | None -> Right (length args)) arities
+    let body = stmts_of_expr arities body
+    let Cons (Local (locals', _), def) = make_lambda name args body
+    (arities, def ++ code, locals' ++ locals)
+  | Ffi_def { name, fent, arity } ->
+    let fspec =
+      match Strings.split_on " " fent with
+      | [file, func] ->
+        pasted_files := Set.insert file !pasted_files
+        func
+      | [func] -> func
+      | _ -> error @@ "Foreign spec too big: " ^ fent
+    let args = [ gensym () | with _ <- [1 .. arity] ]
+    let Cons (Local (locals', _), def) = make_lambda name args [Return (Lcall_e (var fspec, var <$> args))]
+    (arities, def ++ code, locals' ++ locals)
+
+let get_file_contents () =
+  let files = Set.members !pasted_files
+  let go contents path =
+    let f = open_for_reading path
+    let x = read_all f
+    close_file f
+    match x with
+    | Some s -> "--- foreign file: " ^ path ^ "\n" ^ s ^ "\n" ^ contents
+    | None -> contents
+  foldl go "" files
\ No newline at end of file
diff --git a/stg/stg.ml b/stg/stg.ml
new file mode 100644
index 0000000..c719922
--- /dev/null
+++ b/stg/stg.ml
@@ -0,0 +1,53 @@
+module Set = import "data/set.ml"
+open import "prelude.ml"
+
+type update_flag = Updatable | Function
+
+type lambda_form 'a <- { name : string, free_vars : Set.t string, args : list string, update : update_flag, body : 'a }
+
+type stg_atom =
+  | Var of string
+  | Int of int
+
+type stg_pattern =
+  | Con_pat of int * list string
+  | Default
+
+type stg_primitive =
+  | Add
+  | Sub
+  | Mul 
+  | Div
+  | Equ
+
+type stg_expr =
+  | Let  of list (lambda_form stg_expr) * stg_expr
+  | Case of stg_expr  * string * list (stg_pattern * stg_expr)
+  | App  of stg_atom  * list stg_atom
+  | Con  of int * int * list stg_atom
+  | Prim of stg_primitive * list stg_atom
+  | Atom of stg_atom
+
+type stg_def =
+  | Fun     of { name : string, args : list string, body : stg_expr, is_con : option int }
+  | Ffi_def of { name : string, fent : string, arity : int }
+
+let stg_fv =
+  let rec go = function
+    | Atom a -> go_atom a
+    | Let (lfs, e) ->
+      let fv = go e
+      fv `Set.difference` Set.from_list (map (.name) lfs)
+    | App (a, args) -> foldl Set.union Set.empty (map go_atom (a::args))
+    | Con (_, _, i) -> foldl Set.union Set.empty (map go_atom i)
+    | Case (ex, binder, pats) ->
+      foldl go_pat (go ex) pats
+        |> Set.delete binder
+    | Prim (_, args) -> foldl Set.union Set.empty (map go_atom args)
+  and go_atom = function
+    | Int _ -> Set.empty
+    | Var e -> Set.singleton e
+  and go_pat set = function
+    | Default, e -> Set.union set (go e)
+    | Con_pat (_, args), e -> Set.union set (go e `Set.difference` Set.from_list args)
+  go
\ No newline at end of file
diff --git a/tc.ml b/tc.ml
index 61199e0..eb798b0 100644
--- a/tc.ml
+++ b/tc.ml
@@ -425,7 +425,11 @@ let tc_program value_exports type_exports (prog : list decl) =
     | [Foreign (Fimport {var, ftype}) as def] ->
         let ty_scope' = add_missing_vars M.empty ftype
         let t = check_is_type (M.union ty_scope' ty_scope) ftype
-        (dt_info, M.insert var (Forall { vars = M.keys ty_scope', body = t } |> Poly) val_scope, ty_scope, def :: out)
+        (
+          dt_info,
+          M.insert var (Forall { vars = M.keys ty_scope', body = t } |> Poly) val_scope,
+          ty_scope, def :: out
+        )
     | Cons (Foreign (Fimport {var}), _) ->
         error @@ "Foreign definition " ^ var ^ " is part of a group.  How?"
     | Cons (Decl (name, args, body), ds) ->