wip: stack frames

2026-08-28 11:39:37 -06:00
parent 49292d5d01
commit c0a44c89b4
6 changed files with 349 additions and 117 deletions
@@ -0,0 +1,88 @@
+* example
+
+#+begin_src scheme
+  (letrec ((fac (λ (n)
+                (if (zero? n)
+                    1
+                    (* n (fac (- n 1)))))))
+  (fac 3))
+#+end_src
+
+#+begin_src scheme
+  (λ (ktail0)
+  (letrec ((fac
+            (λ (n ktail1)
+              (zero?
+               n
+               (κ (x0)
+                  (if x0
+                      (continue ktail1 1)
+                      (- n 1
+                         (κ (x1)
+                            (fac x1
+                                 (κ (x2)
+                                    (* n x2 ktail1)))))))))))
+    (fac 3)))
+#+end_src
+
+#+begin_example
+n ktail1
+| |
+| | x0
+| | |
+| | ^
+| |
+| | x1
+| | |
+| | ^
+| | 
+| | x2
+| | |
+^ ^ ^
+#+end_example
+
+#+begin_src scheme
+  (define $fac-c0
+    (pop! %x0 0) ; [ x0 $fac-c0 n $fac ktail1 ]
+    (if %x0 ; [ $fac-c0 n $fac ktail1 ]
+        ;; every variable but `ktail1' is dead so we pop them all.
+        ;; this probably means that `if' should take two continuations
+        ;; rather than two blocks.
+        (then (pop! %_) ; [ $fac-c0 n $fac ktail1 ]
+              (pop! %_) ; [ n $fac ktail1 ]
+              (pop! %_) ; [ $fac ktail1 ]
+              (push! 1) ; [ ktail1 ]
+              (return 1)) ; [ 1 ktail1 ]
+        (else (load! %n 1) ; [ $fac-c0 n $fac ktail1 ]
+              (prim %x1 (- %n 1)) ; [ $fac-c0 n $fac ktail1 ]
+              (push! $fac-c1) ; [ $fac-c0 n $fac ktail1 ]
+              (push! $fac) ; [ $fac-c1 $fac-c0 n $fac ktail1 ]
+              (push! %x1) ; [ $fac $fac-c1 $fac-c0 n $fac ktail1 ]
+              (call 1) ; [ x1 $fac $fac-c1 $fac-c0 n $fac ktail1 ]
+              )))
+
+  (define $fac-c1
+    (pop! %x2) ; [ x2 $fac-c1 $fac-c0 n $fac ktail1 ]
+    (load! %n 3) ; [ $fac-c1 $fac-c0 n $fac ktail1 ]
+    (prim %x3 (* %n %x2))
+    (push! %x3) ; [ $fac-c1 $fac-c0 n $fac ktail1 ]
+    (return 1) ; [ x3 $fac-c1 $fac-c0 n $fac ktail1 ]
+    )
+
+  (define $fac
+    (load! %ktail1 2) ; [ n $fac ktail1 ]
+    (load! %n 0) ; [ n $fac ktail1 ]
+    (push! $fac-c0) ; [ n $fac ktail1 ]
+    (push! $zero?) ; [ $fac-c0 n $fac ktail1 ]
+    (push! %n) ; [ $zero? $fac-c0 n $fac ktail1 ]
+    (call 1) ; [ n $zero? $fac-c0 n $fac ktail1 ]
+    )
+
+  (define $start
+    (push! $fac) ; [ $start ktail0 ]
+    (push! 3) ; [ $fac $start ktail0 ]
+    (tail-call 1) ; [ 3 $fac $start ktail0 ]
+    ;; ↑ `tail-call' knows how to dispose of the caller's stack frame.
+    )
+#+end_src
+