Add optimization cases for triage and composition

src/Eval.hs

@@ -59,8 +59,21 @@ evalAST env term
 elimLambda :: TricuAST -> TricuAST
 elimLambda = go
   where
+    -- η-reduction
     go (SLambda [v] (SApp f (SVar x)))
       | v == x && not (isFree v f) = elimLambda f
+    -- Triage optimization
+    go (SLambda [a] (SLambda [b] (SLambda [c] body))) 
+      | body == triageBody         = _TRIAGE
+      where
+        triageBody =
+          (SApp (SApp TLeaf (SApp (SApp TLeaf (SVar a)) (SVar b))) (SVar c))
+    -- Compose optimization
+    go (SLambda [f] (SLambda [g] (SLambda [x] body))) 
+      | body == composeBody = _COMPOSE
+      where
+        composeBody = SApp (SVar f) (SApp (SVar g) (SVar x))
+    -- General elimination
     go (SLambda (v:vs) body)
       | null vs                    = toSKI v (elimLambda body)
       | otherwise                  = elimLambda (SLambda [v] (SLambda vs body))
@@ -75,10 +88,13 @@ elimLambda = go
       | otherwise        = SApp (SApp _S (toSKI x n)) (toSKI x u)
     toSKI x t
       | not (isFree x t) = SApp _K t
+      | otherwise        = errorWithoutStackTrace "Unhandled toSKI conversion"
 
-    _S = parseSingle "t (t (t t t)) t"
-    _K = parseSingle "t t"
-    _I = parseSingle "t (t (t t)) t"
+    _S       = parseSingle "t (t (t t t)) t"
+    _K       = parseSingle "t t"
+    _I       = parseSingle "t (t (t t)) t"
+    _TRIAGE  = parseSingle "t (t (t t (t (t (t t t))))) t"
+    _COMPOSE = parseSingle "t (t (t t (t (t (t t t)) t))) (t t)"
     
     isFree x = Set.member x . freeVars
     freeVars (SVar    v    ) = Set.singleton v