From c9145d854b31b48e4f699321148ce07564f46372 Mon Sep 17 00:00:00 2001
From: Krasimir Angelov <kr.angelov@gmail.com>
Date: Thu, 19 Feb 2026 15:40:01 +0100
Subject: [PATCH] started working on a termination checker

---
 .../api/GF/Compile/TerminationCheck.hs        | 71 +++++++++++++++++++
 src/compiler/gf.cabal                         |  1 +
 2 files changed, 72 insertions(+)
 create mode 100644 src/compiler/api/GF/Compile/TerminationCheck.hs

diff --git a/src/compiler/api/GF/Compile/TerminationCheck.hs b/src/compiler/api/GF/Compile/TerminationCheck.hs
new file mode 100644
index 000000000..07de1991a
--- /dev/null
+++ b/src/compiler/api/GF/Compile/TerminationCheck.hs
@@ -0,0 +1,71 @@
+{-# LANGUAGE BangPatterns #-}
+module GF.Compile.TerminationCheck where
+
+import GF.Grammar
+import Debug.Trace
+
+callGraph m c (ps,t) =
+  let (_,xs) = foldl (\(i,xs) p -> (i+1,patts i EQ xs p)) (0,[]) ps
+      cs     = calls m 0 xs t [] []
+  in trace (show (c,cs)) $ return ()
+
+patts i ord xs (PP _ ps)    = foldl (patts i LT) xs ps
+patts i ord xs (PV x)
+  | x /= identW             = (x,(i,ord)):xs
+patts i ord xs (PR as)      = foldl (\xs (_,p) -> patts i ord xs p) xs as
+patts i ord xs (PT ty p)    = patts i ord xs p
+patts i ord xs (PAs x p)    = patts i ord ((x,(i,ord)):xs) p
+patts i ord xs (PImplArg p) = patts i ord xs p
+patts i ord xs (PSeq _ _ p1 _ _ p2) = patts i LT (patts i LT xs p1) p2
+patts i ord xs _            = xs
+
+
+calls m i xs (App t1 t2) args cs =
+  let args' = case t2 of
+                Vr x -> case lookup x xs of
+                          Just (j,ord) -> (i,j,ord):args
+                          Nothing -> args
+                _    -> args
+  in calls m (i+1) xs t1 args' (calls m 0 xs t2 [] cs)
+calls m i xs (Q (m',q)) args cs
+  | m == m' =
+      let args' = [(i-i'-1,j,ord) | (i',j,ord) <- args]
+      in (q,args') : cs
+calls m i xs _ args cs = cs
+
+
+matmul a b =
+  sum [(i,k,mul ord1 ord2) | (i ,j,ord1) <- a
+                           , (j',k,ord2) <- b
+                           , j==j'
+                           ]
+      []
+  where
+    sum []                 ys = ys
+    sum (x@(i,k,ord) : xs) ys = sum xs (accumulate ys)
+      where
+        accumulate []      = [x]
+        accumulate (y@(i',k',ord') : ys)
+          | i==i' && k==k' = let !sum = add ord ord'
+                             in (i',k',sum):ys
+          | otherwise      = y : accumulate ys
+
+    add LT LT = LT
+    add LT EQ = LT
+    add LT GT = LT
+    add EQ LT = LT
+    add EQ EQ = EQ
+    add EQ GT = EQ
+    add GT LT = LT
+    add GT EQ = EQ
+    add GT GT = GT
+
+    mul LT LT = LT
+    mul LT EQ = LT
+    mul LT GT = GT
+    mul EQ LT = LT
+    mul EQ EQ = EQ
+    mul EQ GT = GT
+    mul GT LT = GT
+    mul GT EQ = GT
+    mul GT GT = GT
diff --git a/src/compiler/gf.cabal b/src/compiler/gf.cabal
index 14ba590f3..db3e9c6ae 100644
--- a/src/compiler/gf.cabal
+++ b/src/compiler/gf.cabal
@@ -123,6 +123,7 @@ library
     GF.Compile.Tags
     GF.Compile.ToAPI
     GF.Compile.TypeCheck
+    GF.Compile.TerminationCheck
     GF.Compile.Update
     GF.Data.BacktrackM
     GF.Data.Graph