cont stack example

examples/cont-stack/Shakefile.hs

@@ -0,0 +1,21 @@
+import Development.Shake
+import Development.Shake.Command
+import Development.Shake.FilePath
+import Development.Shake.Util
+
+main = shakeArgs shakeOptions $ do
+  -- action $ do
+  --   sourceFiles <- getDirectoryFiles "" ["//*.luasm"]
+  --   need $ (-<.> "luac") <$> sourceFiles
+  want ["cont-stack.wasm"]
+  alternatives $ do
+    "*.wasm" %> \out -> do
+        let wat = out -<.> "wat"
+        need [wat]
+        cmd_ "wasm-tools parse" [wat] "-o" [out]
+  phony "run" $ do
+    need ["cont-stack.wasm"]
+    cmd_ "./run.js"
+  phony "clean" $ do
+    removeFilesAfter ".shake" ["//*"]
+    liftIO $ removeFiles "." ["*.wasm"]

examples/cont-stack/cont-stack.wat

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+(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))))

examples/cont-stack/run.js

@@ -0,0 +1,14 @@
+#!/usr/bin/env node
+const fs = require('node:fs');
+
+const imports = {
+    guppy: {
+        print: (arg) => console.log (arg)
+    }
+}
+
+const wasmBuffer = fs.readFileSync ('cont-stack.wasm');
+WebAssembly.instantiate (wasmBuffer, imports).then (wasmModule => {
+    const { main } = wasmModule.instance.exports;
+    main ()
+});