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