Add a tutorial on Juvix module to JS interop via Wasm

docs/org/SUMMARY.org

@@ -6,6 +6,8 @@
   - [[./getting-started/quick-start.md][Quick start]]
   - [[./getting-started/dependencies.md][Installing dependencies]]
 - [[./examples/README.md][Juvix Examples]]
+- [[./tutorials/README.md][Tutorials]]
+  - [[./tutorials/nodejs-interop.md][NodeJS Interop]]
 
 - [[./language-reference/README.md][Language reference]]
   - [[./language-reference/comments.md][Comments]]

docs/org/tutorials/README.org

@@ -0,0 +1 @@
+  - [[./nodejs-interop.md][NodeJS Interop]]

docs/org/tutorials/nodejs-interop.org

@@ -0,0 +1,108 @@
+* NodeJS Interop
+
+A Juvix module can be compiled to a Wasm module. When a Wasm module is
+instantiated by a host, functions from the host can be injected into a Wasm
+module and functions from the Wasm module can be called by the host.
+
+In this tutorial you will see how to call host functions in Juvix and call Juvix
+functions from the host using the Wasm mechanism.
+
+** The Juvix module
+
+The following Juvix module has two functions.
+
+The function =hostDisplayString= is an =axiom= with no corresponding =compile=
+block that implements it. We will inject an implementation for this function
+when we instantiate the module from NodeJS.
+
+The function =juvixRender= is a normal Juvix function. We will call this from
+NodeJS.
+
+#+begin_src
+-- NodeJsInterop.juvix
+module NodeJsInterop;
+
+open import Stdlib.Prelude;
+
+axiom hostDisplayString : String → IO;
+
+juvixRender : IO;
+juvixRender ≔ hostDisplayString "Hello World from Juvix!";
+
+end;
+#+end_src
+
+** Compiling the Juvix module
+
+The Juvix module can be compiled using the following command:
+
+#+begin_src
+juvix compile -r standalone NodeJsInterop.juvix
+#+end_src
+
+This will create a file containing a Wasm module called =NodeJsInterop.wasm=.
+
+** The NodeJS module
+
+The following NodeJS module demonstrates both calling a Juvix function from
+NodeJS and injecting a NodeJS function into a Juvix module.
+
+The NodeJS function =hostDisplayString= is passed to the Wasm module
+=NodeJSInterop.wasm= when it is instantiated. After instantiation the Juvix
+function =juvixRender= is called.
+
+The functions =ptrToCstr= and =cstrlen= are necessary to convert the =char=
+pointer passed from Juvix to a JS =String=.
+
+#+begin_src
+-- NodeJSInterop.js
+const fs = require('fs');
+let wasmModule = null;
+
+function cstrlen(mem, ptr) {
+    let len = 0;
+    while (mem[ptr] != 0) {
+        len++;
+        ptr++;
+    }
+    return len;
+}
+
+function ptrToCstr(ptr) {
+    const wasmMemory = wasmModule.instance.exports.memory.buffer;
+    const mem = new Uint8Array(wasmMemory);
+    const len = cstrlen(mem, ptr);
+    const bytes = new Uint8Array(wasmMemory, ptr, len);
+    return new TextDecoder().decode(bytes);
+}
+
+function hostDisplayString(strPtr) {
+    const text = ptrToCstr(strPtr);
+    console.log(text);
+}
+
+const wasmBuffer = fs.readFileSync("NodeJsInterop.wasm");
+WebAssembly.instantiate(wasmBuffer, {
+    env: {
+        hostDisplayString,
+    }
+}).then((w) => {
+    wasmModule = w;
+    wasmModule.instance.exports.juvixRender();
+});
+#+end_src
+
+** Running the Wasm module
+
+Now you should have the files =NodeJsInterop.wasm= and =NodeJsInterop.js= in the
+same directory. Run the following command to execute the module:
+
+#+begin_src
+node NodeJsInterop.js
+#+end_src
+
+You should see the following output:
+
+#+begin_src
+Hello World from Juvix!
+#+end_src

tests/positive/MiniC/ImportExportName/Input.juvix

@@ -2,15 +2,9 @@ module Input;
 
 open import Stdlib.Prelude;
 
-axiom Void : Type;
+axiom hostDisplayString : String → IO;
 
-compile Void {
-  c ↦ "void";
-};
-
-axiom hostDisplayString : String → Void;
-
-juvixRender : Void;
+juvixRender : IO;
 juvixRender ≔ hostDisplayString "Hello World from Juvix!";
 
 end;

tests/positive/MiniC/ImportExportName/input.js

@@ -11,16 +11,16 @@ function cstrlen(mem, ptr) {
     return len;
 }
 
-function ptrToCstr(wasmMemory, ptr) {
+function ptrToCstr(ptr) {
+    const wasmMemory = wasmModule.instance.exports.memory.buffer;
     const mem = new Uint8Array(wasmMemory);
     const len = cstrlen(mem, ptr);
     const bytes = new Uint8Array(wasmMemory, ptr, len);
     return new TextDecoder().decode(bytes);
 }
 
 function hostDisplayString(strPtr) {
-    const wasmMemory = wasmModule.instance.exports.memory.buffer;
-    const text = ptrToCstr(wasmMemory, strPtr);
+    const text = ptrToCstr(strPtr);
     console.log(text);
 }