feat: ffi example

data/ffi.ts

@@ -0,0 +1,56 @@
+/**
+ * @title Foreign Function Interface
+ * @difficulty intermediate
+ * @tags cli
+ * @run --unstable --allow-ffi <url>
+ * @resource {https://docs.deno.com/runtime/manual/runtime/ffi_api} Manual: FFI
+ * @resource {https://denonomicon.deno.dev} Denonomicon
+ *
+ * Foreign Function Interface (FFI) is a way to call functions written in other languages from JavaScript.
+ */
+
+// Prerequisites:
+// - Julia from https://julialang.org/downloads/ installed
+// - `julia` in your `PATH`
+
+// This example shows how to use the julia FFI library to execute Julia code from Deno.
+
+// First lets define the symbols we want to import from the library.
+const SYMBOLS = {
+  // The `jl_init` function initializes the Julia runtime.
+  jl_init: {
+    // The function takes no parameters so we pass an empty array.
+    parameters: [],
+    // The function returns a `void` pointer.
+    result: "void",
+  },
+  // The `jl_eval_string` function takes a string and evaluates it as Julia code.
+  jl_eval_string: {
+    // The function takes a string so we pass an array with a buffer type
+    parameters: ["buffer"],
+    // The function results in a `pointer`.
+    result: "pointer",
+  },
+} as const;
+
+// Next, we import the FFI library from Deno.
+const julia = Deno.dlopen(
+  // Change .dll to .dylib on macOS and .so on Linux
+  `libjulia.dll`,
+  SYMBOLS,
+).symbols;
+
+// Before we can call the functions we need to convert the string to a C string. Let's define a helper function for that.
+export function cstr(str: string): Uint8Array {
+  const buf = new Uint8Array(str.length + 1);
+  new TextEncoder().encodeInto(str, buf);
+  return buf;
+}
+
+// We can now call the functions we imported.
+julia.jl_init();
+
+// We can now evaluate Julia code.
+julia.jl_eval_string(
+  cstr("println(sqrt(2.0))"),
+);

toc.ts

@@ -129,6 +129,7 @@ export const TOC: TocGroup[] = [
     title: "Advanced",
     icon: IconStars,
     items: [
+      "ffi",
       "web-workers",
       "webassembly",
     ],