2026-08-17 16:17:53 -06:00
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+#+title: ABI
+
+largely based on the Guile Hoot's [[https://codeberg.org/spritely/hoot/src/branch/main/design/ABI.md][ABI]].
+
+* calling convention
+
+** non-tail calls
+
+- set the global variable ~$current-closure~ to the callee's closure.
+- load arguments into globals ~$arg0~, ~$arg1~, ~$arg2~, …
+- push return continuation onto ~$cont-stack~
+
+* scratchpad
+
+#+begin_src scheme
+  ;; Scheme source
+  (define (silly f g h x)
+    (f (h x) (g x)))
+
+
+  ;; continuation-passing style
+  (define (silly f g h x ktail)
+    (h x (κ (x0)
+            (g x (κ (x1)
+                    (f x0 x1 ktail))))))
+
+  ;; with explicit stacks
+  (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))
+#+end_src