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fix: freeVars, toSKIDB

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freeVars did not descend into TStem, TFork, or SList, so dependency analysis
under structural nodes and lists was silently missed.

toSKIDB's _other = _K `SApp` TLeaf fallback returned a constant leaf when the
binder occurred under a structural node, losing the abstraction entirely.
Replace with explicit lowering: BStem/BFork/BList are converted to application
form before SKI abstraction, and any other unsupported DB term errors explicitly
This commit is contained in:
James Eversole
2026-05-07 11:04:29 -05:00
parent e8ab61dbaa
commit 1d84bf7cfa
2 changed files with 35 additions and 220 deletions
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13
src/Eval.hs
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@@ -223,6 +223,9 @@ freeVars (SVar v Nothing) = Set.singleton v
freeVars (SVar v (Just _)) = Set.singleton v
freeVars (SApp t u) = Set.union (freeVars t) (freeVars u)
freeVars (SLambda vs body) = Set.difference (freeVars body) (Set.fromList vs)
freeVars (TStem t) = freeVars t
freeVars (TFork t u) = Set.union (freeVars t) (freeVars u)
freeVars (SList xs) = foldMap freeVars xs
freeVars _ = Set.empty
reorderDefs :: Env -> [TricuAST] -> [TricuAST]
@@ -394,12 +397,10 @@ toSKIDB t
| not (dependsOnLevel 0 t) = SApp _K (fromDBClosed t)
toSKIDB (BVar 0) = _I
toSKIDB (BApp n u) = SApp (SApp _S (toSKIDB n)) (toSKIDB u)
toSKIDB (BList xs) =
let anyUses = any (dependsOnLevel 0) xs
in if not anyUses
then SApp _K (SList (map fromDBClosed xs))
else SList (map toSKIDB xs)
toSKIDB _other = _K `SApp` TLeaf
toSKIDB (BStem t) = toSKIDB (BApp BLeaf t)
toSKIDB (BFork l r) = toSKIDB (BApp (BApp BLeaf l) r)
toSKIDB (BList xs) = toSKIDB (foldr (\m r -> BApp (BApp BLeaf m) r) BLeaf xs)
toSKIDB other = error $ "toSKIDB: unsupported DB term: " ++ show other
app2 :: TricuAST -> TricuAST -> TricuAST
app2 f x = SApp f x