return, pushcall

doc/liveness.org

@@ -0,0 +1,88 @@
+* example
+
+#+begin_src scheme
+  (letrec ((fac (λ (n)
+                (if (zero? n)
+                    1
+                    (* n (fac (- n 1)))))))
+  (fac 3))
+#+end_src
+
+#+begin_src scheme
+  (λ (ktail0)
+  (letrec ((fac
+            (λ (n ktail1)
+              (zero?
+               n
+               (κ (x0)
+                  (if x0
+                      (continue ktail1 1)
+                      (- n 1
+                         (κ (x1)
+                            (fac x1
+                                 (κ (x2)
+                                    (* n x2 ktail1)))))))))))
+    (fac 3)))
+#+end_src
+
+#+begin_example
+n ktail1
+| |
+| | x0
+| | |
+| | ^
+| |
+| | x1
+| | |
+| | ^
+| | 
+| | x2
+| | |
+^ ^ ^
+#+end_example
+
+#+begin_src scheme
+  (define $fac-c0
+    (pop! %x0 0) ; [ x0 $fac-c0 n $fac ktail1 ]
+    (if %x0 ; [ $fac-c0 n $fac ktail1 ]
+        ;; every variable but `ktail1' is dead so we pop them all.
+        ;; this probably means that `if' should take two continuations
+        ;; rather than two blocks.
+        (then (pop! %_) ; [ $fac-c0 n $fac ktail1 ]
+              (pop! %_) ; [ n $fac ktail1 ]
+              (pop! %_) ; [ $fac ktail1 ]
+              (push! 1) ; [ ktail1 ]
+              (return 1)) ; [ 1 ktail1 ]
+        (else (load! %n 1) ; [ $fac-c0 n $fac ktail1 ]
+              (prim %x1 (- %n 1)) ; [ $fac-c0 n $fac ktail1 ]
+              (push! $fac-c1) ; [ $fac-c0 n $fac ktail1 ]
+              (push! $fac) ; [ $fac-c1 $fac-c0 n $fac ktail1 ]
+              (push! %x1) ; [ $fac $fac-c1 $fac-c0 n $fac ktail1 ]
+              (call 1) ; [ x1 $fac $fac-c1 $fac-c0 n $fac ktail1 ]
+              )))
+
+  (define $fac-c1
+    (pop! %x2) ; [ x2 $fac-c1 $fac-c0 n $fac ktail1 ]
+    (load! %n 3) ; [ $fac-c1 $fac-c0 n $fac ktail1 ]
+    (prim %x3 (* %n %x2))
+    (push! %x3) ; [ $fac-c1 $fac-c0 n $fac ktail1 ]
+    (return 1) ; [ x3 $fac-c1 $fac-c0 n $fac ktail1 ]
+    )
+
+  (define $fac
+    (load! %ktail1 2) ; [ n $fac ktail1 ]
+    (load! %n 0) ; [ n $fac ktail1 ]
+    (push! $fac-c0) ; [ n $fac ktail1 ]
+    (push! $zero?) ; [ $fac-c0 n $fac ktail1 ]
+    (push! %n) ; [ $zero? $fac-c0 n $fac ktail1 ]
+    (call 1) ; [ n $zero? $fac-c0 n $fac ktail1 ]
+    )
+
+  (define $start
+    (push! $fac) ; [ $start ktail0 ]
+    (push! 3) ; [ $fac $start ktail0 ]
+    (tail-call 1) ; [ 3 $fac $start ktail0 ]
+    ;; ↑ `tail-call' knows how to dispose of the caller's stack frame.
+    )
+#+end_src
+

doc/make-vm-stackier.org

@@ -0,0 +1,68 @@
+* rationale?
+
+previously, the VM's stack was used for storing local variables across blocks; a Scheme procedure was split into several low-level routines (one for the procedure itself and one for each continuation), and the stack was used as a communication channel for these separate routines. in contrast, registers were local to each routine. this aligns with Wasm's model of functions pretty well, with Wasm /locals/ acting as the VM's /registers/, and a global mutable stack serving as fallback.
+
+this worked quite well until it became time to implement ~call/cc~.
+
+we are considering making the following alterations to the VM:
+- explicitly segment the stack into frames.
+- passing procedures and return addresses on the stack.
+
+* scratchpad
+
+** Scheme source
+
+#+begin_src scheme
+(* 2 (call/cc
+      (λ (cc)
+        (begin (cc 6)
+               3))))
+#+end_src
+
+** CPS
+
+#+begin_src scheme
+(λ (ktail0)
+  (letrec ((with-cc
+            (λ (cc ktail1)
+              (letrec ((k0 (κ (_)
+                              (continue ktail1 3))))
+                (cc 6 k0)))))
+    (prim (call/cc with-cc)
+          (κ (x1)
+             (prim (* 2 x1)
+                   (κ (x2) (continue ktail0 x2)))))))
+#+end_src
+
+** stack VM
+
+#+begin_src scheme
+;; (call n) expects `n' values on the stack as arguments. then the
+;; procedure is expected at index `n', and the return continuation
+;; should be at `n+1'.
+
+(define $k0
+  (pop! %_) ; [ _ ret ]
+  (push! 3) ; [ ret ]
+  (tail-call 1) ; [ 3 ret ]
+  )
+
+(define $with-cc
+  (pop! %cc) ; [ cc ret ]
+  (push! $k0) ; [ ret ]
+  (push! %cc) ; [ $k0 ret ]
+  (push! 6) ; [ cc $k0 ret ]
+  ;; call a procedure with one argument.
+  (call 1) ; [ 6 cc $k0 ret ]
+  )
+
+(define $main
+  (pop! %ktail0) ; [ ret ]
+  (prim %x1 (call/cc $with-cc)) ; []
+  (prim %x2 (* 2 %x1)) ; []
+  (push! %ktail0) ; []
+  (push! %x2) ; [ ret ]
+  (tail-call 1) ; [ %x2 ret ]
+  )
+#+end_src
+

src/Gyehoek/CPS/Convert.hs

@@ -47,18 +47,18 @@ convert (Scm.ExpLit l) k = k . one . ValImm $ case l of
   _ -> _
 
 -- special case: call/cc is desugared during cps-conversion...
-convert (Scm.ExpPrim (PrimCallCC withcc)) k = do
+-- convert (Scm.ExpPrim (PrimCallCC withcc)) k = do
-  convert1 withcc \withcc' -> do
+--   convert1 withcc \withcc' -> do
-    cc <- gensym' @Name "cc"
+--     cc <- gensym' @Name "cc"
-    r <- gensym' "r"
+--     r <- gensym' "r"
-    m <- k . one $ ValVar r
+--     m <- k . one $ ValVar r
-    ccish <- gensym' @Name "cc-ish"
+--     ccish <- gensym' @Name "cc-ish"
-    x <- gensym' @Name "x"
+--     x <- gensym' @Name "x"
-    pure [cps|
+--     pure [cps|
-      (letrec ((#{cc} (κ (#{r}) #{m})))
+--       (letrec ((#{cc} (κ (#{r}) #{m})))
-        (letrec ((#{ccish} (λ (#{x} _) (continue #{cc} #{x}))))
+--         (letrec ((#{ccish} (λ (#{x} _) (continue #{cc} #{x}))))
-          (#{withcc'} #{ccish} #{cc})))
+--           (#{withcc'} #{ccish} #{cc})))
-    |]
+--     |]
 
 -- ...while all other prims are left as-is for later stages to
 -- handle..

src/Gyehoek/CPS/Stackify.hs

@@ -48,12 +48,12 @@ stackify
   => Env -> Exp -> Eff es BlockBuilder
 
 stackify g (ExpLetRec [(f, AbsKappa kap)] e) = do
-  stackifyKappa g f kap \g' kap' -> do
+  stackifyKappa g (MkLabel f) kap \g' kap' -> do
     emitRoutine kap'
     stackify g' e
 
 stackify g (ExpLetRec [(f, AbsLambda lam)] e) = do
-  stackifyLambda g f lam \g' lam' -> do
+  stackifyLambda g (MkLabel f) lam \g' lam' -> do
     emitRoutine lam'
     stackify g' e
 
@@ -63,69 +63,61 @@ stackify g (ExpIf c t f) = do
   f' <- buildBlock <$> stackify g f
   pure . Tail $ Stk.If c' t' f'
 
-stackify g (ExpApply f xs ktail) = pure $
+-- stackify g (ExpApply f xs ktail) = pure $
-    Code [ Stk.Push (Stk.ValReg l) | l <- ls ] $
+--     Code [ Stk.Push (Stk.ValReg l) | l <- ls ] $
-    Tail (Stk.TailCall (stackifyVal g f) (k : (stackifyVal g <$> xs)))
+--     Tail (Stk.TailCall (stackifyVal g f) (k : (stackifyVal g <$> xs)))
-  where
+--   where
-    k = var g ktail
+--     k = var g ktail
-    ls = fold $ (k ^? #ValImm . #ImmLabel)
+--     ls = fold $ (k ^? #ValImm . #ImmLabel)
-      >>= \klbl -> g ^. #liveness . at klbl
+--       >>= \klbl -> g ^. #liveness . at klbl
 
-stackify g e@(ExpContinue k xs) = do
+-- stackify g e@(ExpContinue k xs) = do
-  pure $
-    Code [ Stk.Push (Stk.ValReg l) | l <- ls ] $
-    Tail (Stk.TailCall k' (stackifyVal g <$> xs))
-  where
-    k' = stackifyVal g k
-    ls = fold $ (k' ^? #ValImm . #ImmLabel)
-      >>= \klbl -> g ^. #liveness . at klbl
-
--- stackify g (ExpPrim (PrimCallCC withcc) cc) = do
---   cc_l <- gensym' "cc"
---   rcc_l <- gensym' "reified-cc"
---   stackifyKappa g cc_l cc \g' rt -> do
---     emitRoutine rt
 --   pure $
---       Code [ Stk.Prim rcc_l $ PrimReifyCC (Stk.ValLabel cc_l) ] $
+--     Code [ Stk.Push (Stk.ValReg l) | l <- ls ] $
---       Tail (Stk.TailCall (stackifyVal g' withcc) [Stk.ValLabel rcc_l])
+--     Tail (Stk.TailCall k' (stackifyVal g <$> xs))
+--   where
+--     k' = stackifyVal g k
+--     ls = fold $ (k' ^? #ValImm . #ImmLabel)
+--       >>= \klbl -> g ^. #liveness . at klbl
 
 stackify g (ExpPrim p (MkKappa [x] e)) = do
-  e' <- stackify (g & #bound . at x ?~ Stk.ValReg x) e
+  e' <- stackify (g & #bound . at x ?~ Stk.ValReg (MkReg x)) e
   pure $
-    Code [ Stk.Prim x (stackifyVal g <$> p) ] e'
+    Code [ Stk.Prim (MkReg x) (stackifyVal g <$> p) ] e'
 
 stackify _ e = error [i|unimplemented exp: #{e}|]
 
 -- affine
 _ValName :: Traversal' Val Name
-_ValName = failing #ValVar (#ValImm . #ImmLabel)
+_ValName = failing #ValVar (#ValImm . #ImmLabel . #MkLabel)
 
 stackifyKappa
   :: (Stackify :> es, GenSym :> es)
-  => Env -> Name -> Kappa
+  => Env -> Label -> Kappa
   -> (Env -> Stk.Routine -> Eff es r)
   -> Eff es r
-stackifyKappa g name kap@(MkKappa xs m) w = do
+stackifyKappa g name kap@(MkKappa xs m) w = _
-  let vs = (name, Stk.ValLabel name) : (bindReg <$> xs)
+-- stackifyKappa g name kap@(MkKappa xs m) w = do
-  let ls = live g kap
+--   let vs = (name, Stk.ValLabel name) : (bindReg <$> xs)
-  m' <- stackify (g & #bound <>~ H.fromList (vs ++ (bindReg <$> ls))) m
+--   let ls = live g kap
-  let g' = g & #bound . at name ?~ Stk.ValLabel name
+--   m' <- stackify (g & #bound <>~ H.fromList (vs ++ (bindReg <$> ls))) m
-             & #liveness . at name ?~ live g kap
+--   let g' = g & #bound . at name ?~ Stk.ValLabel name
-  let rt = Stk.MkRoutine name xs . buildBlock $
+--              & #liveness . at name ?~ live g kap
-       -- pop in the opposite order we push
+--   let rt = Stk.MkRoutine name xs . buildBlock $
-       Code [Stk.Pop x | x <- reverse ls] m'
+--        -- pop in the opposite order we push
-  w g' rt
+--        Code [Stk.Pop x | x <- reverse ls] m'
+--   w g' rt
 
 stackifyLambda
   :: (Stackify :> es, GenSym :> es)
-  => Env -> Name -> Lambda
+  => Env -> Label -> Lambda
   -> (Env -> Stk.Routine -> Eff es r)
   -> Eff es r
 stackifyLambda g name (MkLambda xs k m) w = do
-  let vs = [ (x, Stk.ValReg x) | x <- k:xs ]
+  let vs = [ (x, Stk.ValReg (MkReg x)) | x <- k:xs ]
   m' <- stackify (g & #bound <>~ H.fromList vs) m
-  let g' = g & #bound . at name ?~ Stk.ValLabel name
+  let g' = g & #bound . at (name ^. wrappedIso) ?~ Stk.ValLabel name
-  w g' $ Stk.MkRoutine name (k:xs) (buildBlock m')
+  w g' $ Stk.MkRoutine name (buildBlock m')
 
 stackifyVal :: Env -> Val -> Stk.Val
 stackifyVal g = \case
@@ -136,10 +128,10 @@ stackifyVal g = \case
 var :: Env -> Name -> Stk.Val
 var g v = case g ^. #bound . at v of
   Just x -> x
-  Nothing -> Stk.ValLabel v
+  Nothing -> Stk.ValLabel (MkLabel v)
 
 bindReg :: Name -> (Name, Stk.Val)
-bindReg x = (x, Stk.ValReg x)
+bindReg x = (x, Stk.ValReg (MkReg x))
 
 
 

src/Gyehoek/CPS/Syntax.hs

@@ -18,6 +18,8 @@ module Gyehoek.CPS.Syntax
   , Imm(..)
   , Obj(..)
   , Hob(..)
+  , Label(..)
+  , Reg(..)
   , pattern Halt
   , pattern Halt1
   , _MkKappa
@@ -36,7 +38,7 @@ module Gyehoek.CPS.Syntax
   , Abs(..)
   , Free(..)
   , pattern ValLabel
-  , labelName -- don't like that this is part of the api
+  , pattern ObjLabel
   )
   where
 
@@ -52,6 +54,8 @@ import Gyehoek.Prelude hiding (op)
 import Gyehoek.Sexp (Datum)
 import Gyehoek.Sexp (G, (:-)(..))
 import qualified Data.InvertibleGrammar.Base as IG
+import Gyehoek.GenSym (Gen)
+import Data.String (IsString)
 
 -- Data types
 
@@ -60,13 +64,23 @@ data Val
   | ValVar Name
   deriving (Show, Generic, Data, Eq)
 
-pattern ValLabel :: Name -> Val
+pattern ValLabel :: Label -> Val
 pattern ValLabel x = ValImm (ImmLabel x)
 
+newtype Label = MkLabel { inner :: Name }
+  deriving stock (Generic, Data)
+  deriving newtype (Show, Eq, Gen, IsString, Hashable)
+  deriving anyclass (NFData, Wrapped)
+
+newtype Reg = MkReg { inner :: Name }
+  deriving stock (Generic, Data)
+  deriving newtype (Show, Eq, Gen, IsString, Hashable)
+  deriving anyclass (NFData, Wrapped)
+
 data Imm
   = ImmInt Int
   | ImmBool Bool
-  | ImmLabel Name
+  | ImmLabel Label
   | ImmUndefined
   deriving stock (Show, Generic, Data, Eq)
   deriving anyclass (NFData)
@@ -77,9 +91,11 @@ data Obj
   deriving stock (Show, Generic, Data, Eq)
   deriving anyclass (NFData)
 
+pattern ObjLabel l = ObjImm (ImmLabel l)
+
 -- | a heap object.
 data Hob
-  = HobClosure { label :: Name, env :: List Obj }
+  = HobClosure { label :: Label, env :: List Obj }
   | HobPair Obj Obj
   deriving stock (Show, Generic, Data, Eq)
   deriving anyclass (NFData)
@@ -169,17 +185,25 @@ instance S.DatumIso Imm where
   datumIso = S.match
     $ S.With (. S.int)
     $ S.With (. S.datumIso)
-    $ S.With (. labelName)
+    $ S.With (. S.datumIso)
     $ S.With (. S.unreadable (const "#<undefined>"))
     $ S.End
 
-labelName :: S.DatumGrammar Name
+instance S.DatumIso Label where
-labelName = S.coproduct
+  datumIso = S.with \g -> S.coproduct
     [ S.decorate S.SynConstant >>> S.datumIso @Name >>> S.prismIso
           (S.expected "label")
           (prefixed @Name "$")
     , S.list $ S.el (S.sym "$") >>> S.el (S.datumIso @Name)
     ]
+    >>> g
+
+instance S.DatumIso Reg where
+  datumIso = S.with \g ->
+    S.decorate S.SynVariable >>> S.datumIso @Name >>> S.prismIso
+      (S.expected "register")
+      (prefixed @Name "%")
+    >>> g
 
 instance S.DatumIso Hob where
   datumIso = S.match
@@ -189,7 +213,7 @@ instance S.DatumIso Hob where
     where
       conspair = S.dottedList (S.el S.datumIso) S.datumIso
       -- closures can be printed, but not parsed.
-      closure :: G (Datum :- t) (List Obj :- Name :- t)
+      closure :: G (Datum :- t) (List Obj :- Label :- t)
       closure = IG.Flip $ IG.PartialIso
         (\(env:-code:-t) -> S.Unreadable "#<procedure>" :- t)
         (const . Left $ mempty)

src/Gyehoek/Prelude.hs

@@ -19,6 +19,7 @@ module Gyehoek.Prelude
   , (>>>)
   , (>=>)
   , (<=<)
+  , wrappedIso
   ) where
 
 import Control.Lens hiding (List, (:<))
@@ -40,4 +41,5 @@ import Data.List.NonEmpty (NonEmpty((:|)))
 import Numeric.Natural (Natural)
 import Control.Category ((>>>))
 import Control.Monad
+import Data.Generics.Wrapped (Wrapped(..))
 

src/Gyehoek/Scheme/Syntax.hs

@@ -84,6 +84,7 @@ data Prim e
   | PrimEnvRef e Int
   | PrimEnvCode e
   | PrimCallCC e
+  | PrimCaptureCC
   | PrimValues (List e)
   | PrimCallWithValues e e
   deriving stock (Show, Generic, Functor, Foldable, Traversable, Data, Eq)
@@ -164,17 +165,18 @@ primDatumIso namefn a = S.match
     $ S.With (. ht1 "integer?")
     $ S.With (. ht1 "write")
     $ S.With (. ht1 "zero?")
-    $ S.With (. nullop "newline")
+    $ S.With (. ht0 "newline")
     $ S.With (. ht1' "make-closure")
     $ S.With (. S.headTagged2 (namefn "env-ref") a S.int)
     $ S.With (. ht1 "env-code")
     $ S.With (. ht1 "call/cc")
+    $ S.With (. ht0 "capture/cc")
     $ S.With (. ht0' "values")
     $ S.With (. ht2 "call-with-values")
     $ S.End
     where
       idn = S.el . S.sym . namefn
-      nullop s = S.list $ idn s
+      ht0 s = S.list $ idn s
       ht1 s = S.headTagged1 (namefn s) a
       ht2 s = S.headTagged2 (namefn s) a a
       ht1' s = S.headTagged1' (namefn s) a a

src/Gyehoek/Stack/Syntax.hs

@@ -14,8 +14,11 @@ module Gyehoek.Stack.Syntax
   , Imm(..)
   , Hob(..)
   , Prim(..)
-  , Name
+  , Name(..)
+  , Reg(..)
+  , Label(..)
   , pattern ValLabel
+  , pattern ObjLabel
   , stkP
   ) where
 
@@ -24,13 +27,13 @@ import qualified Gyehoek.Sexp as S
 import Gyehoek.Scheme.Syntax (Name(..), Lit(..), Prim(..))
 import GHC.Exts (IsList(..))
 import Data.List (intersperse)
-import Gyehoek.CPS.Syntax (Imm(..), Obj(..), Hob(..), labelName)
+import Gyehoek.CPS.Syntax (Imm(..), Obj(..), Hob(..), pattern ObjLabel, Reg, Label)
 import Gyehoek.Prelude
 import Gyehoek.Sexp ((:-)((:-)))
 
 
 newtype Program = MkProgram
-  { routines :: HashMap Name Routine
+  { routines :: HashMap Label Routine
   }
   deriving stock (Show, Generic, Data)
   deriving newtype (Semigroup, Monoid)
@@ -44,8 +47,7 @@ instance IsList Program where
   toList = toListOf $ #routines . each
 
 data Routine = MkRoutine
-  { label :: Name
+  { label :: Label
-  , params :: List Name
   , start :: Block
   }
   deriving stock (Show, Generic, Data)
@@ -59,25 +61,31 @@ data Block = MkBlock
   deriving anyclass (NFData)
 
 data Tail
-  = TailCall Val (List Val)
+  -- | call the procedure at stack index `n` supplied with `n`
+  -- arguments on top of the stack, then return by calling the
+  -- continuation at stack index `n+1`.
+  = TailCall Int
+  | Call Int
   | If Val Block Block
+  | Return Int
   deriving stock (Show, Generic, Data)
   deriving anyclass (NFData)
 
 data Instr
-  = Pop Name
+  = Pop Reg
   | Push Val
-  | Prim Name (Prim Val)
+  | Load Reg
+  | Prim Reg (Prim Val)
   deriving stock (Show, Generic, Data)
   deriving anyclass (NFData)
 
 data Val
-  = ValReg Name
+  = ValReg Reg
   | ValImm Imm
   deriving stock (Show, Generic, Data, Eq)
   deriving anyclass (NFData)
 
-pattern ValLabel :: Name -> Val
+pattern ValLabel :: Label -> Val
 pattern ValLabel x = ValImm (ImmLabel x)
 
 
@@ -87,9 +95,10 @@ pure []
 
 instance S.DatumIso Instr where
   datumIso = S.match
-    $ S.With (S.headTagged1 "pop!" regName >>>)
+    $ S.With (S.headTagged1 "pop!" S.datumIso >>>)
     $ S.With (S.headTagged1 "push!" S.datumIso >>>)
-    $ S.With (S.headTagged2 "prim" regName S.datumIso >>>)
+    $ S.With (S.headTagged1 "load!" S.datumIso >>>)
+    $ S.With (S.headTagged2 "prim" S.datumIso S.datumIso >>>)
     $ S.End
     where
 
@@ -103,10 +112,13 @@ instance S.DataIso Block where
 
 instance S.DatumIso Tail where
   datumIso = S.match
-    $ S.With (S.headTagged1' "tail-call" S.datumIso S.datumIso >>>)
+    $ S.With (S.headTagged1 "tail-call" S.datumIso >>>)
+    $ S.With (S.headTagged1 "call" S.datumIso >>>)
     $ S.With (if_ >>>)
+    $ S.With (S.headTagged1 "return" S.datumIso >>>)
     $ S.End
     where
+      -- if_ = S.ifLike "if" (S.datumIso @Val) S.datumIso S.datumIso
       if_ = S.ifLike "if" (S.datumIso @Val) (branch "then") (branch "else")
       branch :: Text -> S.DatumGrammar Block
       branch s =
@@ -116,7 +128,7 @@ instance S.DatumIso Tail where
 
 instance S.DatumIso Val where
   datumIso = S.match
-    $ S.With (regName >>>)
+    $ S.With (S.datumIso >>>)
     $ S.With (S.datumIso >>>)
     $ S.End
 
@@ -124,16 +136,11 @@ instance S.DatumIso Routine where
   datumIso = S.with \rout ->
       S.listWithIndentation (S.NSpecial 1)
        ( S.el (S.decorate S.SynBuiltin >>> S.sym "define")
-       >>> S.el (S.list $ S.el labelName >>> S.rest regName)
+       >>> S.el (S.datumIso @Label)
        >>> S.restData (S.dataIso @Block)
        )
       >>> rout
 
-regName :: S.DatumGrammar Name
-regName = S.decorate S.SynVariable >>> S.datumIso @Name >>> S.prismIso
-  (S.expected "register")
-  (prefixed @Name "%")
-
 instance S.DataIso Program where
   dataIso = S.dataIso @(List Routine) >>> S.iso fromList toList
 

src/Gyehoek/Stack/VM.hs

@@ -12,7 +12,7 @@ module Gyehoek.Stack.VM
 import Gyehoek.Stack.Syntax
 import Control.Lens
 import qualified Data.HashMap.Strict as H
-import Data.List (unfoldr, intersperse)
+import Data.List (unfoldr, intersperse, compareLength)
 import Gyehoek.Prelude
 import qualified Data.List.NonEmpty as NE
 import Lucid
@@ -30,25 +30,55 @@ import Control.DeepSeq (deepseq, ($!!))
 import Data.String (fromString)
 
 
--- | inessential information maintained only to aide in debugging.
+-- | non-essential information maintained only to aide in debugging.
 data DebugVM = MkDebugVM
-  { currentRoutine :: Name
+  { currentRoutine :: Label
   }
   deriving (Show, Generic)
 
+newtype Frame = MkFrame { locals :: List Obj }
+  deriving (Show, Generic)
+
+returnAddress :: Traversal' Frame Label
+returnAddress = #locals . _last . #ObjImm . #ImmLabel
+
+newtype Stack = MkStack { frames :: NonEmpty Frame }
+  deriving (Show, Generic)
+
 data VM = MkVM
-  { stack :: List Obj
+  { stack :: Stack
   , code :: List Instr
   , tail :: Tail
-  , registers :: HashMap Name Obj
+  , registers :: HashMap Reg Obj
   , stdout :: Text
   , result :: Maybe (List Obj)
   , debug :: DebugVM
   }
   deriving (Show, Generic)
 
+instance Cons Frame Frame Obj Obj where
+  _Cons = prism'
+    (\(x,MkFrame xs) -> MkFrame (x:xs))
+    \case
+      MkFrame (x:xs) -> Just (x, MkFrame xs)
+      MkFrame [] -> Nothing
+
+pushes :: Foldable f => f Obj -> Frame -> Frame
+pushes = flip $ foldr cons
+
+_NonEmpty :: Iso (NonEmpty a) (NonEmpty b) (a, List a) (b, List b)
+_NonEmpty = iso
+  (\(x:|xs) -> (x,xs))
+  (\(x,xs) -> x:|xs)
+
+pushFrame :: Frame -> Stack -> Stack
+pushFrame f (MkStack xs) = MkStack $ NE.cons f xs
+
+activeFrame :: Lens' VM Frame
+activeFrame = #stack . #frames . _NonEmpty . _1
+
 data Env = MkEnv
-  { labels :: HashMap Name Routine
+  { labels :: HashMap Label Routine
   }
   deriving (Show, Generic)
 
@@ -62,8 +92,8 @@ vmerror = throwError . VMError
 
 stepI :: Jalmot :> es => Env -> VM -> Instr -> Eff es VM
 
-stepI e vm (Push v) = traverseOf #stack push vm
+stepI e vm (Push v) = traverseOf activeFrame push vm
-  where push xs = (:) <$> evalVal e vm v <*> pure xs
+  where push xs = cons <$> evalVal e vm v <*> pure xs
 
 stepI e vm (Prim r p) = traverse (evalVal e vm) p >>= \case
   PrimZeroP x -> case x of
@@ -99,27 +129,84 @@ stepI e vm (Prim r p) = traverse (evalVal e vm) p >>= \case
       ret $ ObjImm (ImmInt (op x y))
     arith_binop _ x y = vmerror [i|bad arith: #{x}, #{y}|]
 
-stepI e vm (Pop r) = case vm ^. #stack of
+stepI e vm (Pop r) = case vm ^? activeFrame . _Cons of
-  [] -> vmerror "empty stack"
+  Nothing -> vmerror "empty stack"
-  (x:xs) -> pure $ vm & #registers . at r ?~ x
+  Just (x,xs) -> pure $ vm & #registers . at r ?~ x
-               & #stack .~ xs
+               & activeFrame .~ xs
 
 stepI e vm ins = vmerror [i|unimplemented instruction: #{ins}|]
 
 stepT :: Jalmot :> es => Env -> VM -> Tail -> Eff es VM
 
-stepT g vm (TailCall f xs) = do
+stepT g vm tc@(Call nargs) =
-  xs' <- traverse (evalVal g vm) xs
+  case parseCall nargs (vm ^. activeFrame) of
-  evalToLabel g vm f >>= \case
+    Nothing -> vmerror "bla"
-    "halt" -> pure $ vm & #result ?~ xs'
+    Just (args,f,ret,frm) ->
-    l -> do
+      case g ^. #labels . at ret of
-      rt <- case g ^. #labels . at l of
+        Nothing -> vmerror [i|undefined label #{ret}|]
-          Nothing -> vmerror [i|undefined label: #{l}|]
+        Just rt -> do
-          Just x -> pure x
+          let newFrame = MkFrame $ args ++ [ObjLabel f,ObjLabel ret]
-      pure $ vm & #code .~ rt.start.code
+          pure $ vm
+            & #code .~ rt.start.code
             & #tail .~ rt.start.tail
-            & #registers .~ H.fromList (rt.params `zip` xs')
+            & activeFrame .~ frm
-            & #debug . #currentRoutine .~ rt.label
+            & #stack %~ pushFrame newFrame
+            & #registers .~ mempty
+
+stepT g vm tc@(Return nret) =
+  case splitAtExact nret (vm ^. activeFrame . #locals) of
+    Nothing -> vmerror [i|bad stack at #{tc}|]
+    Just (xs,_) ->
+      case vm ^? activeFrame . returnAddress of
+        Nothing -> vmerror [i|bad stack #{tc}|]
+        Just "halt" -> pure $ vm & #result ?~ xs
+        Just ra ->
+          case g ^. #labels . at ra of
+            Nothing -> vmerror [i|undefined label #{ra}|]
+            Just rt -> vm
+              & traverseOf (#stack . #frames) \st -> case NE.uncons st of
+                (_, Nothing) -> vmerror "explode"
+                (f, Just fs) -> pure $ fs & _NonEmpty . _1 %~ pushes xs
+
+stepT g vm tc@(TailCall nargs) =
+  case parseTailCall nargs (vm ^. activeFrame) of
+    Nothing -> vmerror [i|bad stack at #{tc}|]
+    Just (args,"halt",_) -> pure $ vm & #result ?~ args
+    Just (args,f,ra) -> do
+      rt <- case g ^. #labels . at f of
+        Nothing -> vmerror [i|undefined label #{f}|]
+        Just x -> pure x
+      let newFrame = MkFrame $ args ++ [ObjLabel f, ObjLabel ra]
+      pure $ vm
+        & #code .~ rt.start.code
+        & #tail .~ rt.start.tail
+        -- replace the active frame; don't push a new one.
+        & activeFrame .~ newFrame
+        -- it is not essential we clear the registers, but it'll
+        -- make bugs more obvious.
+        & #registers .~ mempty
+
+-- stepT g vm tc@(TailCall nargs) =
+--   case setupCall nargs (vm ^. stack) of
+--     Nothing -> vmerror [i|bad stack at #{tc}|]
+--     Just (xs,f,rest) ->
+--       case f of
+--         "halt" -> pure $ vm & #result ?~ xs
+--         l -> do
+--           rt <- case g ^. #labels . at l of
+--             Nothing -> vmerror [i|undefined label: #{l}|]
+--             Just x -> pure x
+--           let ra = vm ^. #activeFrame . #returnAddress
+--           let newFrame = MkFrame $ xs ++ [ObjLabel f, ra]
+--           pure $ vm
+--             & #code .~ rt.start.code
+--             & #tail .~ rt.start.tail
+--             & stack .~ rest
+--             & #frames %~ NE.cons newFrame
+--             -- it is not essential we clear the registers, but it'll
+--             -- make bugs more obvious.
+--             & #registers .~ mempty
+--             & #debug . #currentRoutine .~ rt.label
 
 stepT g vm (If c t f) = do
   branch <- evalVal g vm c <&> \case
@@ -127,7 +214,7 @@ stepT g vm (If c t f) = do
       _ -> t
   pure $ vm & #code .~ branch.code & #tail .~ branch.tail
 
-evalToLabel :: Jalmot :> es => Env -> VM -> Val -> Eff es Name
+evalToLabel :: Jalmot :> es => Env -> VM -> Val -> Eff es Label
 evalToLabel e vm v =
   evalVal e vm v >>= \case
     ObjImm (ImmLabel x) -> pure x
@@ -140,11 +227,40 @@ evalVal e vm = \case
     Just x -> pure x
     Nothing -> vmerror [i|undefined register: #{r}|]
 
+splitAtExact :: Int -> List a -> Maybe (List a, List a)
+splitAtExact n xs = case compareLength xs n of
+  (EQ;GT) -> Just $ splitAt n xs
+  LT -> Nothing
+
+takeExact :: Int -> List a -> Maybe (List a)
+takeExact n xs = case compareLength xs n of
+  (EQ;GT) -> Just $ take n xs
+  LT -> Nothing
+
+parseCall :: Int -> Frame -> Maybe (List Obj, Label, Label, Frame)
+parseCall nargs frm = do
+  (xs,ys) <- splitAtExact (nargs+2) (frm ^. #locals)
+  let (xs',[f,ret]) = splitAt nargs xs
+  f' <- f ^? #ObjImm . #ImmLabel
+  ret' <- ret ^? #ObjImm . #ImmLabel
+  pure (xs',f',ret',MkFrame ys)
+
+parseTailCall :: Int -> Frame -> Maybe (List Obj, Label, Label)
+parseTailCall nargs frm = do
+  (xs,_) <- splitAtExact (nargs+1) (frm ^. #locals)
+  let (xs',f) = xs ^?! _Snoc
+  f' <- f ^? #ObjImm . #ImmLabel
+  pure (xs',f',frm ^?! returnAddress)
+
 initialVM :: VM
 initialVM = MkVM
-  { stack = []
+  { stack = MkStack . NE.singleton . MkFrame $
+    [ ObjLabel "start"
+    , ObjLabel "<nowhere at all>"
+    , ObjLabel "halt"
+    ]
+  , tail = TailCall 0
   , code = []
-  , tail = TailCall (ValLabel "start") [ValLabel "halt"]
   , registers = mempty
   , stdout = ""
   , result = Nothing
@@ -282,16 +398,28 @@ ppVM vm = do
       details_ do
         summary_ do
           var_ [class_ "loc"] . toHtml $ vm ^. #debug . #currentRoutine
-            . re (_Unwrapped' . prefixed "$")
+            . re (prefixed "$" . _Unwrapped' . _Unwrapped')
         pre_ do
           code_ . toHtml . pShowNoColor $ vm
     td_ do
       code_ curi
     td_ do
-      let xs = code_ . ppDatum <$> (vm ^. #stack)
+      let xs = _
       sequence_ $ intersperse " | " xs
   where
     curi = vm ^?! failing (#code . _head . to ppDatum) (#tail . to ppDatum)
 
 ppDatum :: S.DatumIso a => a -> Html ()
 ppDatum = htmlDatum . runJalmotUnsafe . S.toDatum S.datumIso
+
+blah = [stkP|
+        (define $id
+          (return 1))
+        (define $c
+          (return 1))
+        (define $start
+          (push! $c)
+          (push! $id)
+          (push! 123)
+          (call 1))
+      |]

test/Gyehoek/Test/Stack/VM.hs

@@ -13,64 +13,82 @@ evalsTo :: List Obj -> Program -> Assertion
 evalsTo rs p = runJalmotUnsafe (Sut.eval p) @?= rs
 
 test_root = testGroup "stack machine"
-  [ testCase "lit int" do
+  [ testCase "immediate halt" do
+      evalsTo [] [stkP|
+        (define $start
+          (return 0))
+      |]
+  , testCase "lit int" do
       evalsTo [ObjImm (ImmInt 3)] [stkP|
-        (define ($start %ktail)
+        (define $start
-          (tail-call %ktail 3))
+          (push! 3)
+          (return 1))
       |]
-  , testCase "return constant" do
+  , testCase "non-tail identity function" do
       evalsTo [ObjImm (ImmInt 123)] [stkP|
-        (define ($start %ktail)
+        (define $id
-          (tail-call $silly %ktail))
+          (return 1))
-        (define ($silly %ktail)
+        (define $c
-          (tail-call %ktail 123))
+          (return 1))
+        (define $start
+          (push! $c)
+          (push! $id)
+          (push! 123)
+          (call 1))
       |]
-  , testCase "identity continuation" do
+  -- , testCase "return constant" do
-      evalsTo [ObjImm (ImmInt 45)] [stkP|
+  --     evalsTo [ObjImm (ImmInt 123)] [stkP|
-        (define ($start %ktail)
+  --       (define ($start %ktail)
-          (push! %ktail)
+  --         (tail-call $silly %ktail))
-          (tail-call $id 45))
+  --       (define ($silly %ktail)
-        (define ($id %x)
+  --         (tail-call %ktail 123))
-          (pop! %ktail)
+  --     |]
-          (tail-call %ktail %x))
+  -- , testCase "identity continuation" do
-      |]
+  --     evalsTo [ObjImm (ImmInt 45)] [stkP|
-  , testCase "identity function" do
+  --       (define ($start %ktail)
-      evalsTo [ObjImm (ImmInt 45)] [stkP|
+  --         (push! %ktail)
-        (define ($start %ktail)
+  --         (tail-call $id 45))
-          (tail-call $id 45 %ktail))
+  --       (define ($id %x)
-        (define ($id %x %ktail)
+  --         (pop! %ktail)
-          (tail-call %ktail %x))
+  --         (tail-call %ktail %x))
-      |]
+  --     |]
-  , testCase "square" do
+  -- , testCase "identity function" do
-      evalsTo [ObjImm (ImmInt 16)] [stkP|
+  --     evalsTo [ObjImm (ImmInt 45)] [stkP|
-        (define ($start %ktail)
+  --       (define ($start %ktail)
-          (tail-call $square 4 %ktail))
+  --         (tail-call $id 45 %ktail))
-        (define ($square %x %ktail)
+  --       (define ($id %x %ktail)
-          (prim %x2 (* %x %x))
+  --         (tail-call %ktail %x))
-          (tail-call %ktail %x2))
+  --     |]
-      |]
+  -- , testCase "square" do
-  , testCase "factorial" do
+  --     evalsTo [ObjImm (ImmInt 16)] [stkP|
-      let hsfac (n :: Int) = foldr (*) (1) [1..n]
+  --       (define ($start %ktail)
-      let fac (n :: Int) = [stkP|
+  --         (tail-call $square 4 %ktail))
-            (define ($fac %n %ktail)
+  --       (define ($square %x %ktail)
-              (prim %x0 (zero? %n))
+  --         (prim %x2 (* %x %x))
-              (if %x0
+  --         (tail-call %ktail %x2))
-                (then (tail-call %ktail 1))
+  --     |]
-                (else (push! %n)
+  -- , testCase "factorial" do
-                      (push! %ktail)
+  --     let hsfac (n :: Int) = foldr (*) (1) [1..n]
-                      (prim %x1 (- %n 1))
+  --     let fac (n :: Int) = [stkP|
-                      (tail-call $fac %x1 $fac-k0))))
+  --           (define ($fac %n %ktail)
-            (define ($fac-k0 %x2)
+  --             (prim %x0 (zero? %n))
-              (pop! %ktail)
+  --             (if %x0
-              (pop! %n)
+  --               (then (tail-call %ktail 1))
-              (prim %x3 (* %x2 %n))
+  --               (else (push! %n)
-              (tail-call %ktail %x3))
+  --                     (push! %ktail)
-            (define ($start %ktail)
+  --                     (prim %x1 (- %n 1))
-              (tail-call $fac #{n} %ktail))
+  --                     (tail-call $fac %x1 $fac-k0))))
-          |]
+  --           (define ($fac-k0 %x2)
-      evalsTo [ObjImm (ImmInt 1)] $ fac 0
+  --             (pop! %ktail)
-      evalsTo [ObjImm (ImmInt 1)] $ fac 1
+  --             (pop! %n)
-      evalsTo [ObjImm (ImmInt 720)] $ fac 6
+  --             (prim %x3 (* %x2 %n))
-      -- 20 is the greatest `n` for which n! ≤ maxBount @Int
+  --             (tail-call %ktail %x3))
-      evalsTo [ObjImm (ImmInt 2432902008176640000)] $ fac 20
+  --           (define ($start %ktail)
+  --             (tail-call $fac #{n} %ktail))
+  --         |]
+  --     evalsTo [ObjImm (ImmInt 1)] $ fac 0
+  --     evalsTo [ObjImm (ImmInt 1)] $ fac 1
+  --     evalsTo [ObjImm (ImmInt 720)] $ fac 6
+  --     -- 20 is the greatest `n` for which n! ≤ maxBount @Int
+  --     evalsTo [ObjImm (ImmInt 2432902008176640000)] $ fac 20
   ]