cont stack example

2026-07-14 17:35:37 -06:00
parent cd56b176af
commit 42f17c0dac
3 changed files with 119 additions and 0 deletions
@@ -0,0 +1,84 @@
+(module
+ ;; import console.log.
+ (func $print (import "guppy" "print") (param i32))
+
+ ;; declare a table with a reference to $halt in it. idk why, but this
+is ;; necessary to use funcrefs lmfao.
+ (table 2 funcref)
+ (elem (i32.const 0) $halt)
+
+ ;; an array of return continuations.
+ (type $cont (func (param i32)))
+ (type $cont-stack-type (array (mut (ref null $cont))))
+ (global $cont-stack (ref $cont-stack-type)
+         (array.new_default $cont-stack-type (i32.const 128)))
+ (global $cont-stack-top (mut i32) (i32.const 0))
+
+ ;; a global array on which we pass arguments.
+ (type $arg-array-type (array (mut (ref null eq))))
+ (global $arg-array (ref $arg-array-type)
+         (array.new_default $arg-array-type (i32.const 32)))
+
+ ;; cps'd function. takes the number of scheme arguments as the sole
+ ;; wasm argument. arguments are read into locals from
+ ;; $arg-array. does not return, instead popping a continuation from
+ ;; $cont-stack and tail-calling it.
+ (func $add (param $nargs i32)
+       (local $x (ref eq))
+       (local $y (ref eq))
+       (local $return (ref $cont))
+       (local.set $x (ref.as_non_null
+                      (array.get $arg-array-type
+                                 (global.get $arg-array)
+                                 (i32.const 0))))
+       (local.set $y (ref.as_non_null
+                      (array.get $arg-array-type
+                                 (global.get $arg-array)
+                                 (i32.const 1))))
+       (array.set $arg-array-type
+                  (global.get $arg-array)
+                  (i32.const 0)
+                  (ref.i31
+                   (i32.add (i31.get_s (ref.cast (ref i31) (local.get $x)))
+                            (i31.get_s (ref.cast (ref i31) (local.get $y))))))
+       (return_call_ref
+        $cont
+        (i32.const 1)
+        (block (result (ref $cont))
+               (ref.as_non_null
+                (array.get $cont-stack-type
+                           (global.get $cont-stack)
+                           (global.get $cont-stack-top)))
+               (global.set $cont-stack-top
+                           (i32.sub (global.get $cont-stack-top)
+                                    (i32.const 1))))))
+ ;; for demo purposes, this continuation calls console.log and stops.
+ (func $halt (param $nargs i32)
+       (call $print
+             (i31.get_s
+              (ref.cast
+               (ref i31)
+               (ref.as_non_null
+                (array.get $arg-array-type
+                           (global.get $arg-array)
+                           (i32.const 0)))))))
+ ;; entry point }:3
+ (func (export "main")
+       ;; push args
+       (array.set $arg-array-type
+                  (global.get $arg-array)
+                  (i32.const 0)
+                  (ref.i31 (i32.const 4)))
+       (array.set $arg-array-type
+                  (global.get $arg-array)
+                  (i32.const 1)
+                  (ref.i31 (i32.const 5)))
+       ;; push return continuation
+       (array.set $cont-stack-type
+                  (global.get $cont-stack)
+                  (i32.const 0)
+                  (ref.func $halt))
+       ;; make call }:)
+       (return_call $add
+                    ;; inform $add how many arguments we called it with
+                    (i32.const 2))))