From 6713b05872f60c65c7c27700588f44e2edbd4e6b Mon Sep 17 00:00:00 2001
From: James Eversole <james@eversole.co>
Date: Sat, 25 Jan 2025 15:12:28 -0600
Subject: [PATCH] Add optimization cases for triage and composition

---
 lib/base.tri | 11 ++++-------
 src/Eval.hs  | 22 +++++++++++++++++++---
 test/Spec.hs |  3 +--
 3 files changed, 24 insertions(+), 12 deletions(-)

diff --git a/lib/base.tri b/lib/base.tri
index 0208f42..b3e27ae 100644
--- a/lib/base.tri
+++ b/lib/base.tri
@@ -7,17 +7,14 @@ s     = t (t (k t)) t
 m     = s i i
 b     = s (k s) k
 c     = s (s (k s) (s (k k) s)) (k k)
-iC    = (\a b c : s a (k c) b)
-iD    = b (b iC) iC
-iE    = b (b iD) iC
-yi    = (\i : b m (c b (i m)))
-y     = yi iC
-yC    = yi iD
-yD    = yi iE
 id    = (\a : a)
 pair  = t
 if    = (\cond then else : t (t else (t t then)) t cond)
 
+y = ((\mut wait fun : wait mut (\x : fun (wait mut x)))
+     (\x : x x)
+     (\a0 a1 a2 : t (t a0) (t t a2) a1))
+
 triage = (\leaf stem fork : t (t leaf stem) fork)
 test   = triage "Leaf" (\_ : "Stem") (\_ _ : "Fork")
 
diff --git a/src/Eval.hs b/src/Eval.hs
index dcfda2a..2664739 100644
--- a/src/Eval.hs
+++ b/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
diff --git a/test/Spec.hs b/test/Spec.hs
index 71ec7f5..c8ea93a 100644
--- a/test/Spec.hs
+++ b/test/Spec.hs
@@ -497,7 +497,6 @@ fileEval = testGroup "File evaluation tests"
       decodeResult (result res) @?= "\"String test!\""
   ]
 
-
 demos :: TestTree
 demos = testGroup "Test provided demo functionality"
   [ testCase "Structural equality demo" $ do
@@ -511,7 +510,7 @@ demos = testGroup "Test provided demo functionality"
   , testCase "Determining the size of functions" $ do
       library <- liftIO $ evaluateFile "./lib/base.tri"
       res     <- liftIO $ evaluateFileWithContext library "./demos/size.tri"
-      decodeResult (result res) @?= "2071"
+      decodeResult (result res) @?= "454"
   , testCase "Level Order Traversal demo" $ do
       library <- liftIO $ evaluateFile "./lib/base.tri"
       res     <- liftIO $ evaluateFileWithContext library "./demos/levelOrderTraversal.tri"