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|
structure CPS =
struct
fun toCPS (e : Syntax.lexp) (cont : Syntax.value -> Syntax.cexp) : Syntax.cexp =
case e of
Syntax.LVar v => cont (Syntax.VVar v)
| Syntax.LFn (v, expr) =>
let
val fnName = GenSym.new ()
val k = GenSym.new ()
in
Syntax.CFix
([(fnName, [v, k], toCPS expr (fn ret => Syntax.CApp (Syntax.VVar k, [ret])))],
cont (Syntax.VVar fnName))
end
| Syntax.LFix (decls, body) =>
Syntax.CFix
( map
(fn (name, arg, expr) =>
let val w = GenSym.new ()
in
( name
, [arg, w]
, toCPS expr (fn z => Syntax.CApp (Syntax.VVar w, [z]))
)
end)
decls
, toCPS body cont
)
| Syntax.LApp (Syntax.LPrim primop, Syntax.LRecord args) =>
let
val temp = GenSym.new ()
fun go [] acc = Syntax.CPrimop (primop, rev acc, [temp], [cont (Syntax.VVar temp)])
| go (arg :: args) acc = toCPS arg (fn arg' => go args (arg' :: acc))
in go args []
end
| Syntax.LApp (Syntax.LPrim primop, arg) => toCPS (Syntax.LApp (Syntax.LPrim primop, Syntax.LRecord [arg])) cont
| Syntax.LApp (f, x) =>
let
val addr = GenSym.new ()
val arg = GenSym.new ()
in Syntax.CFix
([(addr, [arg], cont (Syntax.VVar arg))],
toCPS f (fn f' =>
toCPS x (fn x' =>
Syntax.CApp (f', [x', Syntax.VVar addr]))))
end
| Syntax.LInt i => cont (Syntax.VInt i)
| Syntax.LString s =>
let val temp = GenSym.new ()
in
Syntax.CRecord
( [(map (fn c => (Syntax.VInt (Char.ord c), [])) (String.explode s), temp)]
, cont (Syntax.VVar temp)
)
end
| Syntax.LRecord [] => cont (Syntax.VInt 0)
| Syntax.LSelect (i, expr) =>
let val temp = GenSym.new ()
in toCPS expr (fn x => Syntax.CSelect (i, x, temp, cont (Syntax.VVar temp)))
end
| Syntax.LRecord exprs =>
let
fun go [] vars =
let val temp = GenSym.new ()
in Syntax.CRecord ([(map (fn v => (v, [])) (rev vars), temp)], cont (Syntax.VVar temp))
end
| go (expr :: exprs) vars =
toCPS expr (fn v => go exprs (v :: vars))
in go exprs []
end
| Syntax.LSwitch (expr, arms, otherwise) =>
let
val sortedArms = Sort.sort (fn ((x, _), (y, _)) => Int.compare (x, y)) arms
val contAddr = GenSym.new ()
val otherwiseAddr = GenSym.new ()
val arg = GenSym.new ()
fun go _ [] cont = Syntax.CApp (Syntax.VVar otherwiseAddr, [])
| go v [(x, arm)] cont =
(case otherwise of
NONE => toCPS arm cont
| SOME _ =>
let val b = GenSym.new ()
in
Syntax.CPrimop
( Syntax.PEq
, [v, Syntax.VInt x]
, [b]
, [ Syntax.CPrimop
( Syntax.PIf
, [Syntax.VVar b]
, []
, [toCPS arm cont, Syntax.CApp (Syntax.VVar otherwiseAddr, [])]
)
]
)
end)
| go v arms cont =
let
val b = GenSym.new ()
val h = length arms div 2
val half1 = List.take (arms, h)
val half2 = List.drop (arms, h)
val (x, _) = hd half2
in
Syntax.CPrimop
( Syntax.PLess
, [v, Syntax.VInt x]
, [b]
, [ Syntax.CPrimop
( Syntax.PIf
, [Syntax.VVar b]
, []
, [go v half1 cont, go v half2 cont]
)
]
)
end
fun contFunc x = Syntax.CApp (Syntax.VVar contAddr, [x])
val fixFuncs = [(contAddr, [arg], cont (Syntax.VVar arg))]
val fixFuncs =
case otherwise of
NONE => fixFuncs
| SOME otherwise => (otherwiseAddr, [], toCPS otherwise contFunc) :: fixFuncs
in
Syntax.CFix
( fixFuncs
, toCPS expr (fn v => go v sortedArms contFunc)
)
end
| _ => raise Fail ("malformed expression " ^ Syntax.lexpToString e)
fun hoist (expr : Syntax.cexp) : Syntax.cexp =
let
fun exprs (Syntax.CRecord (records, k)) = Syntax.CRecord (records, exprs k)
| exprs (Syntax.CSelect (i, arg, res, k)) = Syntax.CSelect (i, arg, res, exprs k)
| exprs (expr as Syntax.CApp _) = expr
| exprs (Syntax.CFix (_, body)) = exprs body
| exprs (Syntax.CPrimop (p, args, res, ks)) = Syntax.CPrimop (p, args, res, (map exprs ks))
fun funs (Syntax.CRecord (_, k)) acc = funs k acc
| funs (Syntax.CSelect (_, _, _, k)) acc = funs k acc
| funs (Syntax.CApp _) acc = acc
| funs (Syntax.CFix (fs, body)) acc =
funs body (foldl (fn ((fName, fVars, fBody), acc) => (fName, fVars, exprs fBody) :: funs fBody acc) acc fs)
| funs (Syntax.CPrimop (_, _, _, ks)) acc = foldl (fn (x, acc) => funs x acc) acc ks
val entryPoint = GenSym.new ()
in
Syntax.CFix ((entryPoint, [], exprs expr) :: funs expr [], Syntax.CApp (Syntax.VLabel entryPoint, []))
end
structure VarMap = Map (type k = Syntax.var
val cmp = Int.compare)
fun varSet (l : Syntax.var list) : unit VarMap.map = VarMap.fromList (map (fn x => (x, ())) l)
fun freeVars (expr : Syntax.cexp) : unit VarMap.map =
case expr of
Syntax.CRecord (records, k) =>
let
val kFreeVars = freeVars k
val argFreeVars =
foldl
(fn ((args, _), acc) =>
VarMap.union acc (varSet (List.mapPartial (fn (Syntax.VVar v, _) => SOME v | _ => NONE) args)))
VarMap.empty
records
val results =
foldl
(fn ((_, res), acc) =>
VarMap.insert res () acc)
VarMap.empty
records
in
VarMap.difference (VarMap.union kFreeVars argFreeVars) results
end
| Syntax.CSelect (_, arg, res, k) =>
let
val argFreeVars =
case arg of
Syntax.VVar v => varSet [v]
| _ => VarMap.empty
val kFreeVars = VarMap.delete res (freeVars k)
in
VarMap.union argFreeVars kFreeVars
end
| Syntax.CApp (func, args) =>
let
val funcFreeVars =
case func of
Syntax.VVar v => varSet [v]
| _ => VarMap.empty
val argFreeVars = varSet (List.mapPartial (fn Syntax.VVar v => SOME v | _ => NONE) args)
in
VarMap.union funcFreeVars argFreeVars
end
| Syntax.CFix (funs, body) =>
let
val names = varSet (map (fn (name, _, _) => name) funs)
val funsFreeVars = map (fn (name, args, fixBody) => VarMap.difference (freeVars fixBody) (varSet args)) funs
val bodyFreeVars = freeVars body
in
foldl (fn (x, acc) => VarMap.union acc (VarMap.difference x names)) VarMap.empty (bodyFreeVars :: funsFreeVars)
end
| Syntax.CPrimop (_, args, res, ks) =>
let
val argFreeVars = varSet (List.mapPartial (fn Syntax.VVar v => SOME v | _ => NONE) args)
val boundVars = varSet res
val kFreeVars = foldl (fn (x, acc) => VarMap.union acc x) VarMap.empty (map (fn k => VarMap.difference (freeVars k) boundVars) ks)
in
VarMap.union argFreeVars kFreeVars
end
fun freeVarsClosure (name, args, body) = map (fn (x, _) => x) (VarMap.toList (VarMap.difference (freeVars body) (varSet args)))
fun enumerate l = ListPair.zip (List.tabulate (length l, (fn x => x)), l)
fun convertExpr varMap expr =
let
fun translate var = getOpt (VarMap.lookup var varMap, var)
fun translateValue (Syntax.VVar v) = Syntax.VVar (translate v)
| translateValue v = v
in
case expr of
Syntax.CRecord (records, k) =>
Syntax.CRecord (map (fn (args, res) => (map (fn (v, p) => (translateValue v, p)) args, res)) records, convertExpr varMap k)
| Syntax.CSelect (i, arg, res, k) =>
Syntax.CSelect (i, translateValue arg, res, convertExpr varMap k)
| Syntax.CApp (func, args) =>
let
val temp = GenSym.new ()
val f = translateValue func
in Syntax.CSelect (0, f, temp,
Syntax.CApp (Syntax.VVar temp, f :: map translateValue args))
end
| Syntax.CFix (funcs, body) =>
let
val convertedFuncs =
map
(fn this as (name, args, body) =>
let
val funcFreeVars = freeVarsClosure this
val varMap' = VarMap.union varMap (VarMap.fromList (map (fn v => (v, GenSym.new ())) funcFreeVars))
val closure = GenSym.new ()
val newBody =
foldl
(fn ((i, x), acc) => Syntax.CSelect (i + 1, Syntax.VVar closure, valOf (VarMap.lookup x varMap'), acc))
(convertExpr varMap' body)
(enumerate funcFreeVars)
in
(GenSym.new (), closure :: args, newBody)
end)
funcs
val newBody =
Syntax.CRecord
( map
(fn (old as (oldName, args, body), (newName, _, _)) =>
let val funcFreeVars = freeVarsClosure old
in ((Syntax.VLabel newName, []) :: map (fn v => (Syntax.VVar (translate v), [])) funcFreeVars, oldName)
end)
(ListPair.zip (funcs, convertedFuncs))
, convertExpr varMap body
)
in
Syntax.CFix (convertedFuncs, newBody)
end
| Syntax.CPrimop (p, args, res, ks) =>
Syntax.CPrimop (p, map translateValue args, res, map (convertExpr varMap) ks)
end
fun convertClosures (expr : Syntax.cexp) : Syntax.cexp = hoist (convertExpr VarMap.empty expr)
end
|
