Web Support by bfeitknecht · Pull Request #65 · bfeitknecht/impli

bfeitknecht · 2026-02-07T21:37:37Z

Closes #58, #51 and #50

Try to hook into Implis TTY
Add workflow badges
Update workflow names
Rename release workflow
fix: WasmWebTerm REPL didn't submit
fix: perhaps super.activate overrides customizations
fix: typo lowercase l
fix: this should do it
Small restructure web/
Progress
Rework everything AGAIN
Proof of concept
Human lints
Always this standard input
Small things matter
Sketch out
Baby steps
God is alive
Holy moly
Example files mapped into WASI FS
Remove redundancy
Copy stub.js to GitHub Pages
Remove Prelude hide

Added badges for release, deployment, tests, and DeepWiki.

Copilot

Pull request overview

This PR reworks the project’s browser/WASM support by replacing the previous wasm-webterm/service-worker approach with a custom xterm.js-based frontend that runs the WASM interpreter via @runno/wasi, plus corresponding JSFFI changes in the Haskell browser REPL and build/deploy updates.

Changes:

Add a new web frontend (web/impli.js) using xterm.js + @runno/wasi, plus an unsupported-browser fallback page.
Update the Haskell WASM entrypoint/REPL to integrate with the browser via JSFFI (prompt export, stdin via JS, :clear/:write via JS hooks).
Adjust build/deploy to generate and ship stub.js, and update workflows/badges/names.

Reviewed changes

Copilot reviewed 15 out of 17 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
web/unsupported.html	Adds a fallback page for browsers without required features.
web/sw.js	Removes the old service-worker-based cross-origin isolation approach.
web/index.html	Switches to importmap-based ES modules and adds unsupported redirects.
web/main.js	Simplifies bootstrapping to a module entry that starts the new `Impli` class.
web/impli.js	Implements the new xterm + WASI runtime and JS hooks consumed by Haskell JSFFI.
web/deno.json	Adds Deno config/tasks for web dev (currently inconsistent with repo contents/deps).
web/deno.lock	Locks Deno/npm dependencies for the web setup.
src/Web.hs	Exports `start` for WASM reactor mode entrypoint.
src/REPL/Execute/Browser.hs	Reworks browser REPL IO to use JSFFI for input/prompt/clear/write.
impli.cabal	Adds WASM reactor/export flags and `ghc-experimental` dependency for browser build.
flake.nix	Adds nodejs and generates `stub.js` via `post-link.mjs` during install.
.github/workflows/deploy.yaml	Copies generated `stub.js` and moves examples into `web/examples/`.
.github/workflows/test.yaml	Renames workflow for consistent casing.
.github/workflows/release.yaml	Renames workflow and trims whitespace.
.github/workflows/format.yaml	Renames workflow and trims whitespace.
README.md	Adds workflow badges.
.gitignore	Ignores generated web artifacts (`impli.wasm`, `stub.js`, `web/examples`).

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Copilot · 2026-02-07T21:43:51Z

src/Web.hs

+import GHC.Wasm.Prim
+
+foreign export javascript "start" main :: IO ()
+


Web.hs introduces foreign export javascript ..., which requires the JavaScriptFFI language extension. This module doesn’t enable it (no {-# LANGUAGE JavaScriptFFI #-} pragma and no default-extensions in the cabal file), so this is likely to fail to compile. Add the pragma at the top of Web.hs (or enable the extension for the impli-web component).

Copilot · 2026-02-07T21:43:51Z

web/impli.js

+    // Open blob in new tab
+    globalThis.open(url, "_blank");


writeIMP opens a new tab via globalThis.open(url, "_blank") without noopener/noreferrer, which allows the opened page to access window.opener in some contexts. Use window.open(url, "_blank", "noopener,noreferrer") (and/or explicitly null out opener) to avoid reverse-tabnabbing-style issues.

Suggested change

// Open blob in new tab

globalThis.open(url, "_blank");

// Open blob in new tab with protections against reverse tabnabbing

const newWindow = globalThis.open(url, "_blank", "noopener,noreferrer");

if (newWindow) {

newWindow.opener = null;

}

Copilot · 2026-02-07T21:43:52Z

web/impli.js

+      // Fetch and instantiate WASM module
+      const wasm = await WebAssembly.instantiateStreaming(fetch("./impli.wasm"), {
+        ...wasi.getImportObject(),
+        ghc_wasm_jsffi: stub(exports),
+      });


WebAssembly.instantiateStreaming(fetch(...)) will throw if the server doesn’t serve .wasm with application/wasm (common in some local dev servers). Add a fallback to fetch(...).then(r => r.arrayBuffer()).then(bytes => WebAssembly.instantiate(bytes, ...)) so local testing and alternate hosting setups don’t break.

Copilot · 2026-02-07T21:43:52Z

web/index.html

+    <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/@xterm/xterm@6.0.0/css/xterm.css" />
+    <link rel="stylesheet" href="./style.css" />
+    <script type="importmap">
+      {
+        "imports": {
+          "@xterm/xterm": "https://cdn.jsdelivr.net/npm/@xterm/xterm@6.0.0/+esm",
+          "@xterm/addon-fit": "https://cdn.jsdelivr.net/npm/@xterm/addon-fit@0.11.0/+esm",
+          "@gytx/xterm-local-echo": "https://cdn.jsdelivr.net/npm/@gytx/xterm-local-echo@0.1.8/+esm",
+          "@runno/wasi": "https://cdn.jsdelivr.net/npm/@runno/wasi@0.10.0/+esm"


The web/README.md still describes the wasm-webterm + service worker architecture and old file layout, but this PR migrates to xterm + @runno/wasi and removes sw.js. Please update the web documentation to match the new setup so local testing/deployment instructions remain accurate.

Copilot · 2026-02-07T21:43:52Z

web/impli.js

+    // Use local-echo to read a line with full editing support
+    const prompt = await this.exports.getPrompt();
+    const line = await this.localEcho.read(prompt);
+    return line + "\n";


readInput() appends a trailing newline (return line + "\n"), but the Haskell REPL loop matches exact strings like "", ":)", and parses meta commands from the raw input. With the newline included, these matches/parses will fail (e.g., ":)\n" won’t match). Return the line without an extra newline (or strip \r?\n on the Haskell side) so the REPL receives the same format as getLine would.

Suggested change

return line + "\n";

// Return the line without an extra newline so it matches Haskell getLine semantics

return line;

Copilot · 2026-02-07T21:43:53Z

src/REPL/Execute/Browser.hs

+foreign export javascript "getPrompt" getPrompt :: JSString
+
+-- | Get the current prompt from the REPL state (prompt + separator + space)
+getPrompt :: JSString
+getPrompt = toJSString prompts
+    where
+        store = unsafePerformIO (readIORef ref)
+        prompts = _prompt store ++ [_separator store] ++ " "


getPrompt is exported as a pure JSString but reads mutable state via unsafePerformIO (readIORef ref). Exporting an IO action (getPrompt :: IO JSString) and reading the IORef normally would avoid unsafePerformIO and make evaluation order/semantics explicit for the JSFFI boundary.

Suggested change

foreign export javascript "getPrompt" getPrompt :: JSString

-- | Get the current prompt from the REPL state (prompt + separator + space)

getPrompt :: JSString

getPrompt = toJSString prompts

where

store = unsafePerformIO (readIORef ref)

prompts = _prompt store ++ [_separator store] ++ " "

foreign export javascript "getPrompt" getPrompt :: IO JSString

-- | Get the current prompt from the REPL state (prompt + separator + space)

getPrompt :: IO JSString

getPrompt = do

store <- readIORef ref

let prompts = _prompt store ++ [_separator store] ++ " "

pure (toJSString prompts)

Copilot · 2026-02-07T21:43:53Z

src/REPL/Execute/Browser.hs

-import REPL.State
+import REPL.State hiding (writeIMP)
+
+-- | Read input from JavaScript (awaits promise from @impli.readIn()@)


The Haddock comment mentions impli.readIn() but the foreign import calls globalThis.impli.readInput(). Update the comment so it matches the actual JS API name.

Suggested change

-- | Read input from JavaScript (awaits promise from @impli.readIn()@)

-- | Read input from JavaScript (awaits promise from @impli.readInput()@)

Copilot · 2026-02-07T21:43:53Z

src/REPL/Execute/Browser.hs

            Reset aspect -> reset aspect
            Show aspect -> shower aspect
            Load path -> loadIMP path
-            Write path -> writeIMP path
+            Write _ -> writeIMP
            AST element -> ast element


Browser :write now ignores the provided FilePath (Write _ -> writeIMP), but the meta-command parser still requires a filepath argument and the help text still says it writes to a file. Consider either (1) using the argument as a suggested filename for the blob/download, or (2) changing the meta command to accept no argument in browser mode (and updating help accordingly) to avoid forcing users to type a dummy path.

Copilot · 2026-02-07T21:43:53Z

web/deno.json

@@ -0,0 +1,13 @@
+{
+  "tasks": {
+    "dev": "deno run --watch main.ts"


deno.json defines a dev task that runs main.ts, but this repository’s web/ directory currently contains main.js and no main.ts. Update the task (or add the missing entrypoint) so deno task dev works as intended.

Suggested change

"dev": "deno run --watch main.ts"

"dev": "deno run --watch main.js"

Copilot · 2026-02-07T21:43:54Z

web/deno.json

+  "imports": {
+    "@/": "./",
+    "@xterm/xterm": "npm:xterm@^5.3.0",
+    "@xterm/addon-fit": "npm:xterm-addon-fit@^0.8.0",
+    "xterm-pty": "npm:xterm-pty@^0.11.1",
+    "@runno/wasi": "npm:@runno/wasi@^0.10.0",
+    "@gytx/xterm-local-echo": "npm:@gytx/xterm-local-echo@^0.1.8"
+  }


The Deno import mappings pin @xterm/xterm to npm:xterm@^5.3.0 and @xterm/addon-fit to the deprecated xterm-addon-fit, while the browser importmap/code uses the scoped @xterm/* packages (and @xterm/xterm@6). Align these dependency definitions (or remove the unused Deno config) to prevent running different, incompatible xterm APIs between local dev and production.

bfeitknecht and others added 24 commits February 3, 2026 18:44

Try to hook into Implis TTY

f3fdd48

Add workflow badges

505668e

Added badges for release, deployment, tests, and DeepWiki.

Update workflow names

e20e869

Rename release workflow

e07ffcc

Merge branch 'develop'

952241b

fix: WasmWebTerm REPL didn't submit

0eabfa7

fix: perhaps super.activate overrides customizations

2e214af

fix: typo lowercase l

1e59211

fix: this should do it

1ef216a

Small restructure web/

bd8fef0

Progress

fe872e9

Rework everything AGAIN

99fa223

Proof of concept

16f10ce

Human lints

d2d334b

Always this standard input

ab463b2

Small things matter

de9704f

Sketch out

48df701

Baby steps

247ec64

God is alive

518de84

Holy moly

b11b225

Example files mapped into WASI FS

fe64a1a

Remove redundancy

79f7f2c

Copy stub.js to GitHub Pages

3d1a43a

Remove Prelude hide

0a91cc9

Copilot AI review requested due to automatic review settings February 7, 2026 21:37

Copilot started reviewing on behalf of bfeitknecht February 7, 2026 21:38 View session

This was linked to issues Feb 7, 2026

Use JS FFI for IO meta-commands #50

Closed

Rework WASM REPL IO #51

Closed

bfeitknecht merged commit b530107 into master Feb 7, 2026
16 of 17 checks passed

Copilot AI reviewed Feb 7, 2026

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Web Support#65

Web Support#65
bfeitknecht merged 24 commits intomasterfrom
echo-ffi

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		import GHC.Wasm.Prim

		foreign export javascript "start" main :: IO ()

-    // Open blob in new tab
-    globalThis.open(url, "_blank");
+    // Open blob in new tab with protections against reverse tabnabbing
+    const newWindow = globalThis.open(url, "_blank", "noopener,noreferrer");
+    if (newWindow) {
+      newWindow.opener = null;
+    }

	return line + "\n";
	// Return the line without an extra newline so it matches Haskell getLine semantics
	return line;

	-- \| Read input from JavaScript (awaits promise from @impli.readIn()@)
	-- \| Read input from JavaScript (awaits promise from @impli.readInput()@)

	"dev": "deno run --watch main.ts"
	"dev": "deno run --watch main.js"

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