wip: abstract stack/continuation machine

doc/abi.org

@@ -0,0 +1,218 @@
+#+title: ABI
+
+largely based on the Guile Hoot's [[https://codeberg.org/spritely/hoot/src/branch/main/design/ABI.md][ABI]].
+
+* calling convention
+
+** non-tail calls
+
+- set the global variable ~$current-closure~ to the callee's closure.
+- load arguments into globals ~$arg0~, ~$arg1~, ~$arg2~, …
+- push return continuation onto ~$cont-stack~
+
+* scratchpad
+
+#+begin_src scheme
+  ;; Scheme source
+  (define (silly f g h x)
+    (f (h x) (g x)))
+
+
+  ;; continuation-passing style
+  (define (silly f g h x ktail)
+    (h x (κ (x0)
+            (g x (κ (x1)
+                    (f x0 x1 ktail))))))
+
+  ;; with explicit stacks
+  (define (silly)
+    (define f (pop!))
+    (define g (pop!))
+    (define h (pop!))
+    (define x (pop!))
+    (define ktail (pop-cont!))
+    (push-cont! (κ (x0)
+                   (define x* (pop!))
+                   (define g* (pop!))
+                   (push-cont! (κ (x1)
+                                  (define f* (pop!))
+                                  (define x0* (pop!))
+                                  (push-cont! ktail)
+                                  (push! x0*)
+                                  (push! x1)
+                                  (call! f)))
+                   (push! x*)
+                   (call! g)))
+    (push! x)
+    (call! h))
+#+end_src
+
+** fac
+
+*** Scheme source
+
+#+begin_src scheme
+(define fac
+  (λ (n)
+    (if (zero? n)
+        1
+        (* n (fac (- n 1))))))
+
+(fac 3)
+#+end_src
+
+*** CPS
+
+#+begin_src scheme
+  (define fac
+  (λ (n ktail)
+    (zero? n (κ (x0)
+                (if x0
+                    1
+                    (- n 1
+                       (κ (x1)
+                          (fac x1
+                               (κ (x2)
+                                  (* n x2 ktail))))))))))
+
+(fac 3 halt)
+
+#+end_src
+
+*** tailified
+
+#+begin_src scheme
+(define (fac-k1)
+  (define n (pop!))
+  (define x2 (pop!))
+  (define x3 (* n x2))
+  (define ktail (pop-cont!))
+  (push! x3)
+  (call! ktail))
+
+(define (fac-k0)
+  (define x0 (pop!))
+  (define n (pop!))
+  (if x0
+      (begin (define ktail (pop-cont!))
+             (push! 1)
+             (call! ktail))
+      (begin (define x1 (- n 1))
+             (push! x1)
+             (push-cont! fac-k1)
+             (call! fac))))
+
+(define (fac)
+  (define n (pop!))
+  (push! n)
+  (push-cont! fac-k0)
+  (push! n)
+  (call! zero?))
+
+(push! 3)
+(push-cont! halt)
+(call! fac)
+#+end_src
+
+evaluation of ~(fac 0)~:
+
+#+begin_src scheme
+(push! 0)                  ; [] []
+(push-cont! halt)          ; [0] []
+(call! fac)                ; [0] [halt]
+(define n (pop!))          ; [0] [halt]
+(push! n)                  ; [] [halt]
+(push-cont! fac-k0)        ; [0] [halt]
+(push! n)                  ; [0] [halt fac-k0]
+(call! zero?)              ; [0 0] [halt fac-k0]
+#<internals of zero?>      ; [0 0] [halt fac-k0]
+(define x0 (pop!))         ; [0 #t] [halt]
+(define n (pop!))          ; [0] [halt]
+(define ktail (pop-cont!)) ; [] [halt]
+(push! 1)                  ; [] []
+(call! ktail)              ; [1] []
+#+end_src
+
+evaluation of ~(fac 3)~
+
+#+begin_src scheme
+(push! 3)                  ; [] []
+(push-cont! halt)          ; [3] []
+(call! fac)                ; [3] [halt]
+
+(define n (pop!))          ; [3] [halt]
+(push! n)                  ; [] [halt]
+(push-cont! fac-k0)        ; [3] [halt]
+(push! n)                  ; [3] [halt fac-k0]
+(call! zero?)              ; [3 3] [halt fac-k0]
+#<internals of zero?>      ; [3 3] [halt fac-k0]
+(define x0 (pop!))         ; [3 #f] [halt]
+(define n (pop!))          ; [3] [halt]
+(define x1 (- n 1))        ; [] [halt]
+(push! n)                  ; [] [halt]
+(push! x1)                 ; [3] [halt]
+(push-cont! fac-k1)        ; [3 2] [halt]
+(call! fac)                ; [3 2] [halt fac-k1]
+
+(define n (pop!))          ; [3 2] [halt fac-k1]
+(push! n)                  ; [3 ] [halt fac-k1]
+(push-cont! fac-k0)        ; [3 2] [halt fac-k1]
+(push! n)                  ; [3 2] [halt fac-k1 fac-k0]
+(call! zero?)              ; [3 2 2] [halt fac-k1 fac-k0]
+#<internals of zero?>      ; [3 2 2] [halt fac-k1 fac-k0]
+(define x0 (pop!))         ; [3 2 #f] [halt fac-k1]
+(define n (pop!))          ; [3 2] [halt fac-k1]
+(define x1 (- n 1))        ; [3] [halt fac-k1]
+(push! n)                  ; [3] [halt fac-k1]
+(push! x1)                 ; [3 2] [halt fac-k1]
+(push-cont! fac-k1)        ; [3 2 1] [halt fac-k1]
+(call! fac)                ; [3 2 1] [halt fac-k1 fac-k1]
+
+(define n (pop!))          ; [3 2 1] [halt fac-k1 fac-k1]
+(push! n)                  ; [3 2] [halt fac-k1 fac-k1]
+(push-cont! fac-k0)        ; [3 2 1] [halt fac-k1 fac-k1]
+(push! n)                  ; [3 2 1] [halt fac-k1 fac-k1 fac-k0]
+(call! zero?)              ; [3 2 1 1] [halt fac-k1 fac-k1 fac-k0]
+#<internals of zero?>      ; [3 2 1 1] [halt fac-k1 fac-k1 fac-k0]
+(define x0 (pop!))         ; [3 2 1 #f] [halt fac-k1 fac-k1]
+(define n (pop!))          ; [3 2 1] [halt fac-k1 fac-k1]
+(define x1 (- n 1))        ; [3 2] [halt fac-k1 fac-k1]
+(push! n)                  ; [3 2] [halt fac-k1]
+(push! x1)                 ; [3 2 1] [halt fac-k1 fac-k1]
+(push-cont! fac-k1)        ; [3 2 1 0] [halt fac-k1 fac-k1]
+(call! fac)                ; [3 2 1 0] [halt fac-k1 fac-k1 fac-k1]
+
+(define n (pop!))          ; [3 2 1 0] [halt fac-k1 fac-k1 fac-k1]
+(push! n)                  ; [3 2 1] [halt fac-k1 fac-k1 fac-k1]
+(push-cont! fac-k0)        ; [3 2 1 0] [halt fac-k1 fac-k1 fac-k1]
+(push! n)                  ; [3 2 1 0] [halt fac-k1 fac-k1 fac-k1 fac-k0]
+(call! zero?)              ; [3 2 1 0 0] [halt fac-k1 fac-k1 fac-k1 fac-k0]
+#<internals of zero?>      ; [3 2 1 0 0] [halt fac-k1 fac-k1 fac-k1 fac-k0]
+(define x0 (pop!))         ; [3 2 1 0 #t] [halt fac-k1 fac-k1 fac-k1]
+(define n (pop!))          ; [3 2 1 0] [halt fac-k1 fac-k1 fac-k1]
+(define ktail (pop-cont!)) ; [3 2 1] [halt fac-k1 fac-k1 fac-k1]
+(push! 1)                  ; [3 2 1 1] [halt fac-k1 fac-k1]
+(call! ktail)              ; [3 2 1 1] [halt fac-k1 fac-k1]
+
+(define n (pop!))          ; [3 2 1 1] [halt fac-k1 fac-k1]
+(define x2 (pop!))         ; [3 2 1] [halt fac-k1 fac-k1]
+(define x3 (* n x2))       ; [3 2] [halt fac-k1 fac-k1]
+(define ktail (pop-cont!)) ; [3 2] [halt fac-k1 fac-k1]
+(push! x3)                 ; [3 2] [halt fac-k1]
+(call! ktail)              ; [3 2 1] [halt fac-k1]
+
+(define n (pop!))          ; [3 2 1] [halt fac-k1]
+(define x2 (pop!))         ; [3 2] [halt fac-k1]
+(define x3 (* n x2))       ; [3] [halt fac-k1]
+(define ktail (pop-cont!)) ; [3] [halt fac-k1]
+(push! x3)                 ; [3] [halt]
+(call! ktail)              ; [3 2] [halt]
+
+(define n (pop!))          ; [3 2] [halt]
+(define x2 (pop!))         ; [3] [halt]
+(define x3 (* n x2))       ; [] [halt]
+(define ktail (pop-cont!)) ; [] [halt]
+(push! x3)                 ; [] []
+(call! ktail)              ; [6] []
+;; => (halt 6)
+#+end_src

doc/closure-conversion.org

@@ -0,0 +1,83 @@
+#+title: closure-conversion
+
+the closure-conversion phase makes closed-over variables explicit by addition of the primitive ~make-closure~, taking a code pointer (in the CPS language, bare lambda) and the environment.
+
+* scratchpad
+
+#+begin_src scheme
+(letrec ((make-adder
+        (lambda (n)
+          (lambda (x)
+            (+ n x)))))
+((make-adder 3) 2))
+#+end_src
+
+#+begin_src scheme
+(define add-code
+  (lambda (n env)
+    (+ n (env-ref env 'x))))
+
+(define make-adder-code
+  (lambda (n)
+    (make-closure add-code ('x n))))
+
+(define make-adder (make-closure make-adder-code))
+
+(apply-closure (apply-closure make-addder 3) 2)
+#+end_src
+
+#+begin_src wat
+(module
+ (type $heap-object (sub (struct (field $hash (mut i32)))))
+ (type $closure (sub $heap-object
+                     (struct (field $hash (mut i32))
+                             (field $code (ref $cont-type)))))
+ (type $closure1 (sub $closure
+                      (struct (field $hash (mut i32))
+                              (field $code (ref $cont-type))
+                              (field $env0 (ref eq)))))
+ (global $arg0 (mut (ref null eq)) (ref.null eq))
+ (global $arg1 (mut (ref null eq)) (ref.null eq))
+ (global $arg2 (mut (ref null eq)) (ref.null eq))
+ (global $arg3 (mut (ref null eq)) (ref.null eq))
+ (global $arg4 (mut (ref null eq)) (ref.null eq))
+ (global $arg5 (mut (ref null eq)) (ref.null eq))
+ ;; ⋮
+ ;; (global $argn (mut (ref null eq)) (ref.null eq))
+
+ (global $current-closure (mut (ref null $closure)) (ref.null $closure))
+
+ (func $add-code (param $nargs i32)
+       (local $n (ref eq))
+       (local $x (ref eq))
+       (local.set $n (global.get $arg0))
+       (local.set $x (struct.get $closure1
+                                 (global.get $current-closure)
+                                 $env0))
+       (return (i32.add $n $x)))
+
+ (func $make-adder-code (param $nargs i32)
+       (local $n (ref eq))
+       (local.set $n (global.get $arg0))
+       (return (struct.new $closure1
+                           0
+                           $add-code)))
+
+ (func $main
+       (local.set $make-adder
+                  (struct.new $closure
+                              0
+                              $make-adder-code))
+       (global.set $current-closure $make-adder)
+       (global.set $arg0 (i32.const 3))
+       (local.set $f (call (struct.get $closure
+                                       $make-adder
+                                       $code)
+                           1))
+       (global.set $current-closure $f)
+       (global.set $arg0 (i32.const 2))
+       (return (call (struct.get $closure
+                                 $f
+                                 $code)
+                     1))))
+#+end_src

doc/notes.org

@@ -0,0 +1,53 @@
+#+title: assorted notes on compilation
+
+* letrec
+
+consider:
+
+#+begin_src scheme
+  (letrec ((even? (lambda (n)
+                    (if (zero? n)
+                        #t
+                        (odd? (- n 1)))))
+           (odd? (lambda (n)
+                   (if (zero? n)
+                       #f
+                       (even? (- n 1))))))
+    (even? 12))
+#+end_src
+
+#+RESULTS:
+: #t
+
+since ~letrec~ is a primitive construct in the CPS language, the translation of mutually recursive functions is straightforward:
+
+#+begin_src scheme
+  (define (-& x y k) (k (- x y)))
+  (define (zero?& x k) (k (zero? x)))
+  (define (halt x) x)
+
+  (letrec ((even? (lambda (n ktail)
+                    (zero?& n
+                            (lambda (x1)
+                              (if x1
+                                  #t
+                                  (-& n 1
+                                      (lambda (x2)
+                                        (odd? x2 ktail))))))))
+           (odd? (lambda (n ktail)
+                   (zero?& n
+                           (lambda (x1)
+                             (if x1
+                                 #f
+                                 (-& n 1
+                                     (lambda (x2)
+                                       (even? x2 ktail)))))))))
+    (even? 12 halt))
+#+end_src
+
+#+RESULTS:
+: #t
+
+however, Scheme permits ~letrec~-expressions with non-lambda right-hand sides, while the CPS language permits only kappa and lambda forms. thus, the handling of these forms is less trivial.
+
+for now we'll just reject any ~letrec~ forms with non-lambda right-hand sides, lol. they aren't very important.

golden/apply2/source.scm

@@ -0,0 +1,5 @@
+((λ (f g x)
+   (f (g x)))
+ (λ (x) (+ x 4))
+ (λ (x) (* x 2))
+ 3)

golden/fn-of-fn/source.scm

@@ -1 +1,3 @@
-(((λ (f) f) (λ (x) (* x 4))) 32)
+(((λ (f) f)
+  (λ (x) (* x 4)))
+ 32)

golden/let-fn/source.scm

@@ -0,0 +1,2 @@
+(let ((square (λ (x) (* x x))))
+  (square 4))

gyehoek.cabal

@@ -61,6 +61,8 @@ library
     Gyehoek.Options
     Gyehoek.Scheme.Syntax
     Gyehoek.Sexp
+    Gyehoek.Stack.Syntax
+    Gyehoek.Stack.VM
     Gyehoek.Wasm
 
   build-depends:
@@ -100,16 +102,21 @@ test-suite test
   type:             exitcode-stdio-1.0
   hs-source-dirs:   test
   main-is:          Main.hs
+
+  -- cabal-fmt: expand test
   other-modules:
     Gyehoek.Test.CPS.Syntax
     Gyehoek.Test.Golden
     Gyehoek.Test.Sexp
+    Gyehoek.Test.Stack.VM
 
   build-depends:
     , base
     , directory
     , filepath
+    , generic-lens
     , gyehoek
+    , lens
     , process-extras
     , sexp-grammar
     , tasty

src/Gyehoek/CPS/Convert.hs

@@ -2,6 +2,7 @@
 {- HLINT ignore "Use camelCase" -}
 module Gyehoek.CPS.Convert
   ( convertProgram
+  , convertExp
   ) where
 
 import Gyehoek.CPS.Syntax
@@ -79,7 +80,6 @@ convert (Scm.ExpLet bs e) k =
         (continue #{kbody} ##{rhss'}))
     |]
 
-
 convert _ k = _
 
 convertProgram :: forall es. (GenSym :> es) => Scm.Program -> Eff es Program
@@ -88,3 +88,6 @@ convertProgram p =
     pure . Halt1 $ case NE.nonEmpty exps of
       Nothing -> ValLit Void
       Just es -> NE.last es
+
+convertExp :: forall es. (GenSym :> es) => Scm.Exp -> Eff es Exp
+convertExp e = convert e (pure . Halt1)

src/Gyehoek/CPS/Syntax.hs

@@ -309,32 +309,53 @@ instance Vars Exp where
 
 
 data Scope
-  = Bind (List Name) Scope
+  = Bind (List Name) (List Scope)
-  | Use (List Name) Scope
+  | Use (List Name) (List Scope)
-  | Leaf
   deriving (Show, Eq)
 
 makeBaseFunctor ''Scope
 
-class Subst a where
-  substWith :: (Name -> Val) -> a -> a
-
-instance Subst Exp where
-  substWith sub = cata \e ->
-    _
-
 class Scoped a where
   scope :: a -> Scope
 
 instance Scoped Kappa where
   scope (MkKappa bs e) =
-    Bind bs (scope e)
+    Bind bs [scope e]
+
+instance Scoped Lambda where
+  scope (MkLambda bs k e) = Bind (bs ++ [k]) [scope e]
+
+instance Scoped Abs where
+  scope = \case
+    AbsKappa k -> scope k
+    AbsLambda l -> scope l
 
 instance Scoped Val where
   scope = \case
-    ValVar x -> Use [x] Leaf
+    ValVar x -> Use [x] []
-    _ -> Leaf
+    _ -> Use [] []
 
 instance Scoped Exp where
   scope = \case
-    ExpApply f xs k = _
+    ExpApply f xs k ->
+      Use (((f:xs) ^.. each . _ValVar) ++ [k]) []
+    ExpLetRec bs e ->
+      Bind (bs ^.. each . _1) $
+        (bs ^.. each . _2 . to scope)
+        ++ [scope e]
+    ExpPrim p k ->
+      Use (p ^.. each . _ValVar) [scope k]
+    ExpContinue k xs ->
+      Use (k : (xs ^.. each . _ValVar)) []
+    ExpIf c t f ->
+      Use (c ^.. _ValVar) [ scope t, scope f ]
+
+
+
+class Subst a where
+  substWith :: (Name -> Maybe Val) -> a -> a
+
+instance Subst Exp where
+  substWith f = go HS.empty where
+    go bound e = case scope e of
+      Use xs ss -> _

src/Gyehoek/Scheme/Syntax.hs

@@ -23,6 +23,8 @@ module Gyehoek.Scheme.Syntax
   , subst
   , getName
   , scm
+  , readExp
+  , readProgram
   )
   where
 
@@ -33,6 +35,7 @@ import Language.SexpGrammar
 import Language.SexpGrammar qualified as Sexp
 import Language.Sexp.Located qualified as S
 import Language.SexpGrammar.Generic
+import Effectful
 import GHC.Generics
 import Prelude hiding ((.), id)
 import Control.Category
@@ -49,6 +52,10 @@ import Data.HashSet (HashSet)
 import qualified Data.HashSet as HS
 import Data.Foldable (fold)
 import Language.Haskell.TH.Quote (QuasiQuoter)
+import Effectful.FileSystem (runFileSystem)
+import qualified Effectful.FileSystem.IO as FS
+import qualified Data.Text.Encoding as T
+import qualified Effectful.FileSystem.IO.ByteString as FB
 
 
 newtype Name = MkName { inner :: Text }
@@ -72,7 +79,8 @@ data Prim e
   | PrimWrite e
   | PrimZeroP e
   | PrimNewline
-  | PrimMakeClosure { code :: e, upvals :: List e }
+  | PrimMakeClosure { code :: e, env :: List e }
+  | PriEnvRef e Int
   deriving (Show, Generic, Functor, Foldable, Traversable, Data, Eq)
 
 instance Each (Prim e) (Prim e') e e'
@@ -157,6 +165,7 @@ primSexpIso namefn a = match
     $ With (. unop "zero?")
     $ With (. nullop "newline")
     $ With (. mkclosure)
+    $ With (. envref)
     $ End
     where
       idn s = el (sym (namefn s))
@@ -164,6 +173,7 @@ primSexpIso namefn a = match
       unop s = list $ idn s >>> el a
       binop s = list $ idn s >>> el a >>> el a
       mkclosure = list $ idn "make-closure" >>> el a >>> rest a
+      envref = list $ idn "env-ref" >>> el a >>> el Sexp.int
 
 instance SexpIso a => SexpIso (Prim a) where
   -- sexpIso = primSexpIso ("prim:"<>) sexpIso
@@ -259,3 +269,22 @@ subst f = \e -> cata go e mempty where
   go (ExpLetF _ _) _ = error "todo lol"
   go (ExpLambdaF bs e) bound = e $ insertFrom bs bound
   go e bound = embed $ fmap ($ bound) e
+
+
+
+fileName :: FilePath -> FilePath
+fileName "-" = "<interactive>"
+fileName e = e
+
+hGetContents :: FS.FileSystem :> es => FS.Handle -> Eff es Text
+hGetContents h = T.decodeUtf8 <$> FB.hGetContents h
+
+readProgram :: IOE :> es => FilePath -> Eff es Program
+readProgram fp = runFileSystem $
+  FS.withFile fp FS.ReadMode $ \h ->
+    Gyehoek.Sexp.parseSexps @CommandOrDef (fileName fp) <$> hGetContents h
+     >>= either error (pure . MkProgram)
+
+readExp :: IOE :> es => FilePath -> Eff es Program
+readExp fp = readProgram fp <&>
+  (^?! (#commandsAndDefs . _head . _Comm))

src/Gyehoek/Sexp.hs

@@ -38,10 +38,12 @@ module Gyehoek.Sexp
   , makeSx'
   , toSexp
   , fromSexp
+  , fromSexp'
   , stripLocation
   , format
   , equivalent
   , encodeOrShow
+  , readSxs
   )
   where
 
@@ -87,6 +89,10 @@ import qualified Data.Vector as V
 import qualified Data.Vector.Strict
 import Data.Function (on)
 import Data.String (IsString (fromString))
+import Effectful
+import qualified Effectful.FileSystem.IO as FS
+import qualified Effectful.FileSystem.IO.ByteString as FB
+import qualified Data.Text.Encoding as T
 
 
 sexp :: SexpIso a => Iso' a Text
@@ -120,6 +126,10 @@ parseSexps :: SexpIso a => FilePath -> Text -> Either String (List a)
 parseSexps f = marshal . SL.parseSexps f . view lazy . encodeUtf8
   where marshal = join . traverseOf (_Right . each) (Sexp.fromSexp sexpIso)
 
+parseSexpsWith :: SexpGrammar a -> FilePath -> Text -> Either String (List a)
+parseSexpsWith g f = marshal . SL.parseSexps f . view lazy . encodeUtf8
+  where marshal = join . traverseOf (_Right . each) (Sexp.fromSexp g)
+
 parseSexp :: SexpIso a => FilePath -> Text -> Either String a
 parseSexp f = marshal . SL.parseSexp f . view lazy . encodeUtf8
   where marshal = join . traverseOf _Right (Sexp.fromSexp sexpIso)
@@ -140,6 +150,24 @@ parseSexpWithPos g pos =
   marshal . SL.parseSexpWithPos pos . view lazy . encodeUtf8
   where marshal = join . traverseOf _Right (Sexp.fromSexp g)
 
+fileName :: FilePath -> FilePath
+fileName "-" = "<interactive>"
+fileName e = e
+
+hGetContents :: FS.FileSystem :> es => FS.Handle -> Eff es Text
+hGetContents h = T.decodeUtf8 <$> FB.hGetContents h
+
+readSxs
+  :: IOE :> es
+  => SexpGrammar a
+  -> FilePath -> Eff es (List a)
+readSxs g fp = FS.runFileSystem $
+  FS.withFile fp FS.ReadMode $ \h ->
+    parseSexpsWith g (fileName fp) <$> hGetContents h
+     >>= either error pure
+
+
+
 nonEmptyGrammar :: Grammar p (NonEmpty x :- t) (List x :- x :- t)
 nonEmptyGrammar = IGB.Iso
   (\((x:|xs) :- t) -> reverse xs :- x :- t)

src/Gyehoek/Stack/Syntax.hs

@@ -0,0 +1,70 @@
+{-# LANGUAGE TemplateHaskellQuotes #-}
+module Gyehoek.Stack.Syntax
+  ( Program(..)
+  , Block(..)
+  , Instr(..)
+  , Val(..)
+  , Lit(..)
+  , Obj(..)
+  , Imm(..)
+  , Prim(..)
+  , Name
+  ) where
+
+import Control.Lens
+import Data.List (List)
+import GHC.Generics (Generic)
+import Data.HashMap.Strict (HashMap)
+import Language.SexpGrammar (SexpIso, (>>>), (:-))
+import Language.SexpGrammar qualified as S
+import Language.SexpGrammar.Generic
+import Data.Coerce (coerce)
+import Data.Text (Text)
+import qualified Gyehoek.Sexp
+import Language.Haskell.TH.Quote (QuasiQuoter)
+import Data.Data (Data)
+import qualified Data.HashMap.Strict as H
+import Effectful
+import Gyehoek.Scheme.Syntax (Name(..), Lit(..), Prim(..))
+
+
+newtype Program = MkProgram
+  { blocks :: List Block
+  }
+  deriving stock (Show, Generic, Data)
+
+data Block = MkBlock
+  { label :: Name
+  , params :: List Name
+  , code :: List Instr
+  }
+  deriving stock (Show, Generic, Data)
+
+instance Each Block Block Instr Instr where
+  each = #code . each
+
+data Instr
+  = Pop Name
+  | Push Val
+  | PopCont Name
+  | PushCont Name
+  | Prim Name (Prim Val)
+  | CallLabel Name (List Val)
+  | CallReg Name (List Val)
+  deriving stock (Show, Generic, Data)
+
+data Val
+  = ValLabel Name
+  | ValReg Name
+  | ValImm Imm
+  deriving stock (Show, Generic, Data, Eq)
+
+data Imm
+  = ImmInt Int
+  | ImmBool Bool
+  deriving stock (Show, Generic, Data, Eq)
+
+data Obj
+  = ObjImm Imm
+  | ObjLabel Name
+  deriving (Show, Generic, Data, Eq)

src/Gyehoek/Stack/VM.hs

@@ -0,0 +1,110 @@
+module Gyehoek.Stack.VM
+  ( VM(..)
+  , Env(..)
+  , eval
+  ) where
+
+import Gyehoek.Stack.Syntax
+import Data.List (List)
+import GHC.Generics (Generic)
+import Control.Lens
+import Data.HashMap.Strict (HashMap)
+import Data.Text (Text)
+import qualified Data.HashMap.Strict as H
+import Data.String.Interpolate (i)
+import Gyehoek.Scheme.Syntax (Sexp(..))
+
+
+data VM = MkVM
+  { stack :: List Obj
+  , kstack :: List Name
+  , code :: List Instr
+  , registers :: HashMap Name Obj
+  , stdout :: Text
+  , result :: Maybe (List Obj)
+  }
+  deriving (Show, Generic)
+
+data Env = MkEnv
+  { blocks :: HashMap Name Block
+  }
+  deriving (Show, Generic)
+
+step :: Env -> VM -> VM
+step e vm = case vm ^. #code of
+  c:cs -> stepI e (vm & #code .~ cs) c
+  _ -> error "halt never called"
+
+stepI :: Env -> VM -> Instr -> VM
+
+stepI e vm (Push v) = vm & #stack %~ (evalVal e vm v :)
+
+stepI e vm (PushCont k) = vm & #kstack %~ (k:)
+
+stepI e vm (Prim r p) = case evalVal e vm <$> p of
+  PrimAdd x y -> arith_binop (+) x y
+  PrimMul x y -> arith_binop (*) x y
+  PrimSub x y -> arith_binop (-) x y
+  PrimDiv x y -> arith_binop div x y
+  x -> error [i|unimplemented prim: #{p}|]
+  where
+    arith_binop op (ObjImm (ImmInt x)) (ObjImm (ImmInt y)) =
+      vm & #registers . at r ?~ ObjImm (ImmInt (op x y))
+    arith_binop _ x y = error [i|bad arith: #{x}, #{y}|]
+
+stepI e vm (Pop r) = case vm ^. #stack of
+  [] -> error "empty stack"
+  (x:xs) -> vm & #registers . at r ?~ x
+               & #stack .~ xs
+
+stepI e vm (PopCont r) = case vm ^. #kstack of
+  [] -> error "empty stack"
+  (x:xs) -> vm & #registers . at r ?~ ObjLabel x
+               & #kstack .~ xs
+
+stepI e vm (CallReg r xs) = stepI e vm (CallLabel l xs)
+  where l = vm ^?! #registers . at r . _Just . #ObjLabel
+
+stepI e vm (CallLabel "halt" xs) = vm & #result ?~ fmap (evalVal e vm) xs
+
+stepI e vm (CallLabel l xs) =
+  vm & #code .~ b.code
+     & #registers .~ fmap (evalVal e vm) (H.fromList $ b.params `zip` xs)
+  where
+    b = case e ^. #blocks . at l of
+      Just x -> x
+      Nothing -> error [i|undefined label: #{l}|]
+
+stepI e vm _ = _
+
+evalVal :: Env -> VM -> Val -> Obj
+evalVal e vm = \case
+  ValImm imm -> ObjImm imm
+  ValReg r -> case vm ^. #registers . at r of
+    Just x -> x
+    Nothing -> error [i|undefined register: #{r}|]
+
+initialVM :: VM
+initialVM = MkVM
+  { stack = []
+  , kstack = ["halt"]
+  , code = [CallLabel "main" []]
+  , registers = mempty
+  , stdout = ""
+  , result = Nothing
+  }
+
+initialEnv :: Program -> Env
+initialEnv (MkProgram bs) = MkEnv
+  { blocks = bs & foldMap \b -> H.singleton b.label b
+  }
+
+loop :: (a -> Either b a) -> a -> b
+loop f a = case f a of
+  Right a' -> loop f a'
+  Left b -> b
+
+eval :: Program -> List Obj
+eval p = initialVM & loop \vm -> case vm ^. #result of
+  Nothing -> Right $ step (initialEnv p) vm
+  Just rs -> Left rs

t.scm

@@ -1,3 +1,21 @@
-(letrec ((x 3)
+(define (-& x y k) (k (- x y)))
-         (y 4))
+(define (zero?& x k) (k (zero? x)))
-  (values x y))
+(define (halt x) x)
+
+(letrec ((even? (lambda (n ktail)
+                  (zero?& n
+                          (lambda (x1)
+                            (if x1
+                                #t
+                                (-& n 1
+                                    (lambda (x2)
+                                      (odd? x2 ktail))))))))
+         (odd? (lambda (n ktail)
+                 (zero?& n
+                         (lambda (x1)
+                           (if x1
+                               #f
+                               (-& n 1
+                                   (lambda (x2)
+                                     (even? x2 ktail)))))))))
+  (even? 12 halt))

test/Gyehoek/Test/Stack/VM.hs

@@ -0,0 +1,50 @@
+module Gyehoek.Test.Stack.VM (root) where
+
+import Test.Tasty (TestTree, testGroup)
+import Test.Tasty.HUnit
+import Gyehoek.Stack.Syntax
+import Gyehoek.Stack.VM qualified as Sut
+import Data.List (List)
+import Control.Lens
+import Data.Generics.Labels
+
+
+root :: IO TestTree
+root = pure . testGroup "stack machine" $
+  [ lit_int
+  , arith
+  ]
+
+
+
+evalsTo :: List Obj -> List Block -> Assertion
+evalsTo rs bs = Sut.eval (MkProgram bs) @?= rs
+
+
+
+lit_int = testCase "lit int" do
+  evalsTo [ObjImm (ImmInt 3)]
+    [ MkBlock "main" []
+      [ PopCont "ktail"
+      , CallReg "ktail" [ValImm (ImmInt 3)]
+      ]
+    ]
+  
+arith = testGroup "arith"
+  [ testCase "multipy" do
+      evalsTo [ObjImm (ImmInt 12)]
+        [ MkBlock "main" []
+          [ PopCont "ktail"
+          , Prim "x1" (PrimMul (ValImm $ ImmInt 3) (ValImm $ ImmInt 4))
+          , CallReg "ktail" [ValReg "x1"]
+          ]
+        ]
+  , testCase "subtract" do
+      evalsTo [ObjImm (ImmInt 14)]
+        [ MkBlock "main" []
+          [ PopCont "ktail"
+          , Prim "x1" (PrimSub (ValImm $ ImmInt 20) (ValImm $ ImmInt 6))
+          , CallReg "ktail" [ValReg "x1"]
+          ]
+        ]
+  ]

test/Main.hs

@@ -5,6 +5,7 @@ import Test.Tasty.Silver.Interactive (defaultMain)
 import qualified Gyehoek.Test.Golden
 import qualified Gyehoek.Test.Sexp
 import qualified Gyehoek.Test.CPS.Syntax
+import qualified Gyehoek.Test.Stack.VM
 
 
 main :: IO ()
@@ -12,8 +13,9 @@ main = defaultMain =<< root
 
 root :: IO TestTree
 root = testGroup "test" <$> sequenceA
-  [ Gyehoek.Test.Golden.root
+  [ {- Gyehoek.Test.Golden.root
-  , Gyehoek.Test.Sexp.root
+  ,-} Gyehoek.Test.Sexp.root
   , Gyehoek.Test.CPS.Syntax.root
+  , Gyehoek.Test.Stack.VM.root
   ]