From fa9621542a6a2d6221bcdeebd335dfbcc826c65d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Madeleine=20Sydney=20=C5=9Alaga?= <msyds@deertopia.net>
Date: Mon, 17 Aug 2026 18:38:05 -0600
Subject: [PATCH]

---
 doc/abi.org | 86 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 t.stk       | 22 --------------
 2 files changed, 86 insertions(+), 22 deletions(-)
 delete mode 100644 t.stk

diff --git a/doc/abi.org b/doc/abi.org
index aa89d0b..439ecb5 100644
--- a/doc/abi.org
+++ b/doc/abi.org
@@ -46,3 +46,89 @@ largely based on the Guile Hoot's [[https://codeberg.org/spritely/hoot/src/branc
     (push! x)
     (call! h))
 #+end_src
+
+** fac
+
+*** Scheme source
+
+#+begin_src scheme
+(define fac
+  (λ (n)
+    (if (zero? n)
+        1
+        (* n (fac (- n 1))))))
+
+(fac 3)
+#+end_src
+
+*** CPS
+
+#+begin_src scheme
+  (define fac
+  (λ (n ktail)
+    (zero? n (κ (x0)
+                (if x0
+                    1
+                    (- n 1
+                       (κ (x1)
+                          (fac x1
+                               (κ (x2)
+                                  (* n x2 ktail))))))))))
+
+(fac 3 halt)
+
+#+end_src
+
+*** tailified
+
+#+begin_src scheme
+(define (fac-k1)
+  (define n (pop!))
+  (define x2 (pop!))
+  (define x3 (* n x2))
+  (define ktail (pop-cont!))
+  (push! x3)
+  (call! ktail))
+
+(define (fac-k0)
+  (define x0 (pop!))
+  (define n (pop!))
+  (if x0
+      (begin (define ktail (pop-cont!))
+             (push! 1)
+             (call! ktail))
+      (begin (define x1 (- n 1))
+             (push! x1)
+             (push-cont! fac-k1)
+             (call! fac))))
+
+(define (fac)
+  (define n (pop!))
+  (push! n)
+  (push-cont! fac-k0)
+  (push! n)
+  (call! zero?))
+
+(push! 3)
+(push-cont! halt)
+(call! fac)
+#+end_src
+
+evaluation of ~(fac 0)~:
+
+#+begin_src scheme
+(push! 0)                  ; [] []
+(push-cont! halt)          ; [0] []
+(call! fac)                ; [0] [halt]
+(define n (pop!))          ; [0] [halt]
+(push! n)                  ; [] [halt]
+(push-cont! fac-k0)        ; [0] [halt]
+(push! n)                  ; [0] [halt fac-k0]
+(call! zero?)              ; [0 0] [halt fac-k0]
+#<internals of zero?>      ; [0 0] [halt fac-k0]
+(define x0 (pop!))         ; [0 #t] [halt]
+(define n (pop!))          ; [0] [halt]
+(define ktail (pop-cont!)) ; [] [halt]
+(push! 1)                  ; [] []
+(call! ktail)              ; [1] []
+#+end_src
diff --git a/t.stk b/t.stk
deleted file mode 100644
index 925fc89..0000000
--- a/t.stk
+++ /dev/null
@@ -1,22 +0,0 @@
-;; -*- mode:scheme -*-
-
-(define (silly)
-  (define f (pop!))
-  (define g (pop!))
-  (define h (pop!))
-  (define x (pop!))
-  (define ktail (pop-cont!))
-  (push-cont! (κ (x0)
-                 (define x* (pop!))
-                 (define g* (pop!))
-                 (push-cont! (κ (x1)
-                                (define f* (pop!))
-                                (define x0* (pop!))
-                                (push-cont! ktail)
-                                (push! x0*)
-                                (push! x1)
-                                (call! f)))
-                 (push! x*)
-                 (call! g)))
-  (push! x)
-  (call! h))