small things

app/Code.hs

@@ -51,7 +51,8 @@ data Cho =
     , _retcut :: Bool -- cut after this goal succeeds
     , _heap :: Heap -- a snapshot of the heap (there's no trail; we rely on CoW copies in other choicepoints)
     , _stk :: [(Code, Scope, [Cho], Bool)] -- remaining goals together with their vars, cuts, and ret-cut flag
-    , _cut :: [Cho] -- snapshot of choicepoints before entering
+    , _cut :: [Cho] -- snapshot of choicepoints before entering the goal
+    , _hcut :: [Cho] -- save of choicepoints just before starting to match head
     }
   deriving (Show)
 

app/Interpreter.hs

@@ -35,6 +35,7 @@ prove g = do
       , _heap = emptyHeap
       , _stk = []
       , _cut = []
+      , _hcut = []
       }
   cho .= []
   loop
@@ -54,10 +55,14 @@ proveStep = do
   import Control.Monad.Trans.Class (lift)
   import System.Console.Haskeline
   g <- use (cur . gol)
+  cho <- use cho
+  cut <- use (cur . cut)
   lift $ do
     outputStrLn $ "STEP (unis="++show u++")"
     outputStrLn $ "head = "++ show h
     outputStrLn $ "goal = "++ show g
+    outputStrLn $ "cut = " ++ show cut
+    outputStrLn $ "cho = " ++ show cho
   -}
   case (u, h) of
     (0, []) -> goalStep
@@ -92,7 +97,7 @@ headStep h = do
   case (h, g) of
     ([Done], _) -> succeedHead
     (Cut:_, _) -> cutHead
-    (Invoke (Builtin bf):_, _) -> advanceHead >> bf
+    (Invoke (Builtin bf):_, _) -> cur . hed .= [Done] >> bf
     (_, [Done]) -> tailCall
     (_, [Cut, Done]) -> tailCut
     (_, _) -> pushCall
@@ -134,7 +139,9 @@ retCut = do
     doCut
     cur . retcut .= False
 
-cutHead = doCut >> advanceHead
+cutHead = do
+  use (cur . hcut) >>= assign cho
+  advanceHead
 
 cutGoal = doCut >> advance
 
@@ -147,7 +154,8 @@ openGoal fn = do
       cur . hvar .= emptyScope
       cur . unis .= arity fn
       cc <- use cur
-      let (newcur:newcho) = [cc & hed .~ h | h <- hs]
+      oldcho <- use cho
+      let (newcur:newcho) = [cc & hcut .~ oldcho & hed .~ h | h <- hs]
       cur .= newcur
       cho %= (newcho ++)
       continue
@@ -162,12 +170,15 @@ pushCall = do
   ngol <- use (cur . hed)
   ngvar <- use (cur . hvar)
   scut <- use (cur . cut)
+  ncut <- use (cur . hcut)
   sretcut <- use (cur . retcut)
   cur . stk %= ((sgol, sgvar, scut, sretcut) :)
   cur . gol .= ngol
   cur . gvar .= ngvar
+  cur . cut .= ncut
   cur . hed .= []
   cur . hvar .= emptyScope
+  cur . hcut .= []
   cur . retcut .= False
   continue
 
@@ -179,6 +190,7 @@ tailCall = do
   cur . gvar .= ngvar
   cur . hed .= []
   cur . hvar .= emptyScope
+  cur . hcut .= []
   continue
 
 tailCut :: InterpFn
@@ -189,8 +201,9 @@ tailCut = do
 
 succeedHead :: InterpFn
 succeedHead = do
-  cur . hvar .= emptyScope
   cur . hed .= []
+  cur . hvar .= emptyScope
+  cur . hcut .= []
   continue
 
 succeedGoal :: InterpFn

inst/prelude.pl

@@ -45,17 +45,8 @@ Ax > Bx :- A is Ax, B is Bx, int2p_lt(B,A).
 Ax >= Bx :- A is Ax, B is Bx, int2p_leq(B,A).
 zero(Ax) :- A is Ax, int1p_zero(A).
 
-gcd(X,Y,R) :- writeln(a), fail.
+gcd(X,Y,R) :- Y > X, !, gcd(Y,X,R).
-gcd(X,Y,R) :- writeln(b), zero(Y), !, R=X.
+gcd(X,Y,R) :- zero(Y), !, R=X.
-gcd(X,Y,R) :- writeln(c), X1 is X mod Y, gcd(Y,X1,R).
+gcd(X,Y,R) :- X1 is X mod Y, gcd(Y,X1,R).
-gcd(X,Y,R) :- writeln(a), Y > X, writeln(wat), !, gcd(Y,X,R).
-gcd(X,Y,R) :- writeln(b), zero(Y), !, R=X.
-gcd(X,Y,R) :- writeln(c), X1 is X mod Y, gcd(Y,X1,R).
 
-test(X) :- writeln(there), zero(X), fail.
+lcm(X,Y,R) :- gcd(X,Y,GCD), R is X*(Y/GCD).
-test(X) :- writeln(here).
-
-test :- writeln(a), a=a, !, fail.
-test :- writeln(b).
-
-xxx :- test.