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2026-05-15 | 🎙️ Word Meter Slice 9a: Real SpeechRecognition Wired Up 🤖

🌅 The Big Moment

🎯 Slice 9a is the moment the Word Meter PureScript port stops being a test-hook puppet show and starts counting actual speech. Up through slice 8, every transcript that ever reached the reducer came in through simulateFinalTranscript on the test hook, which was fantastic for property-based testing but useless if you wanted the meter to do its actual job in a real browser. Slice 9a closes that gap with the simplest configuration that already works in every browser exposing the Web Speech API today: cloud-path recognition with continuous capture and interim results.

🧭 The plan from the slice-9 refinement post called for splitting the original monolithic slice 9 into three smaller end-to-end pieces. Slice 9a is the smallest of those — it makes the meter actually work. Slice 9b will teach it to prefer the on-device path when Chromium exposes the new install-on-demand API, and slice 9c will heal the one runtime failure mode where Chromium says yes to on-device pre-flight and then changes its mind at start() time.

🧱 The Four New Modules

🧩 The slice landed as four new PureScript modules plus targeted edits to the reducer, the application monad environment, and the main orchestrator.

🪶 The first new module is WordMeter.Recognition.Delta, and it is intentionally the simplest one. It has no Effect, no FFI, and no IO of any kind. It exists to encode the legacy integrateFinalizedTranscript decision tree as a single pure function called classifyFinalizedTranscript. The function takes a record with the previous raw finalized transcript and the incoming one, and returns one of four constructors of a sum type called TranscriptIntegration. The constructors are IgnoreDuplicate for the exact-normalized-duplicate case that Android Chrome loves to emit, ExtendUtterance carrying the word delta and the new caption when the incoming transcript is the previous one extended by additional words at a word boundary, StartNewUtterance carrying the full word count and caption when the incoming transcript is a brand new utterance, and IgnoreEarlierSnapshot for the harmless case where the recognizer re-emits an earlier segment of the same utterance. The legacy logic from issue 6897 lives here, in roughly twenty lines of pure code, and is unit-tested branch by branch.

🪟 The second new module is WordMeter.FFI.Recognition, the thin foreign shim over the browser API. Following the convention this repo reinforces every slice, the foreign imports here are dead simple: a constructor lookup, an availability probe, an instance builder, three handler attachers, a handler detacher, and start and stop wrappers. The shim never holds state, never makes decisions, and surfaces every failure mode through a typed return value or a typed callback. The opaque RecognitionInstance newtype is the handle that travels between PureScript and JavaScript, but JavaScript never inspects it — instance lifetime is owned entirely by the capability layer.

🎩 The third new module is WordMeter.Capability.Recognition, the typeclass that production code uses. The AppM instance owns the active recognition instance and the auto-restart timer handle through two new refs in ApplicationEnvironment. The RecordingRecognitionM test newtype records every call site as a constructor of a RecognitionEvent sum type, so the orchestrator’s start, stop, schedule, and cancel calls are observable from unit tests without ever touching a browser. The capability also exposes a recognitionApiAvailable probe so the rest of the program can degrade gracefully when no constructor is present — the meter still loads, the toggle still flips, but the diagnostics drawer records recognition unavailable and the count never moves.

⏱️ The fourth new module is WordMeter.FFI.Timer, a tiny thin shim over window.setTimeout and window.clearTimeout. It exists because the auto-restart logic needs a 250 millisecond delay after every onend event to maintain ambient capture across Chromium’s silence auto-stop. The shim returns an opaque handle that callers pass back to cancel. Like every other FFI in this repo, it carries no policy of its own.

🎼 The Orchestration

🪡 The new orchestration lives in Main.handleToggle, Main.handleReset, Main.handleRecognitionError, and a small family of new helpers in the same file. On the listening edge of the toggle, the orchestrator calls startRecognitionForSession, which queries recognitionApiAvailable, reads the locale from the captured environment snapshot with en-US as the fallback, and hands a record of seven callbacks to startRecognition. The seven callbacks cover every fallible boundary: synchronous construct failure, synchronous start failure, asynchronous onerror events, asynchronous onend events, the success path, the result path, and the error event path. Each failure path records a diagnostic entry with a distinct label so the diagnostics drawer is the single place to find every recognition transition.

🔄 The onend callback is the most interesting one. The recognizer naturally ends after a silence timeout, and the legacy build worked around this by re-issuing start() 250 milliseconds later. The PureScript port reproduces that behavior by first dispatching ResetRecognitionDedupState to clear the per-recognition-run dedup state — without that reset, the next utterance after silence would dedup against whatever was last said — and then scheduling the restart through the new scheduleAutoRestart capability call. When the scheduled callback fires, it checks session.listening one more time, and only then calls startRecognitionForSession again. If the user has stopped listening between the schedule and the fire, the restart is silently skipped.

🛑 The stop path is symmetric. stopRecognitionForSession cancels any pending restart timer first, then asks the capability to detach handlers, clear the env ref, and call stop(). With nothing held in the ref the call is a successful no-op, which lets handleReset and handleRecognitionError call it unconditionally without first checking whether a recognition is actually active.

🪬 The Permission-Denied Path

🛡️ Slice 8 already shipped the typed permission-denied flow, where a not-allowed error from onerror flips the session out of listening, pushes the open interval into the event log, and renders a banner advising the user to grant microphone permission. Slice 9a hooks the new orchestration into that flow without disturbing any of slice 8’s logic. When handleRecognitionError sees that listening was true before the error and is now false after the reducer ran, it calls stopRecognitionForSession followed by releaseHeldWakeLock. The recognition instance is detached, stopped, and forgotten; the wake lock is released; the banner is rendered; and the user sees a clean, consistent UI.

🧪 The Tests

🔬 Slice 9a added three new test functions to the unit suite, on top of the eleven that were already running. runRecognitionDeltaTests exercises every branch of classifyFinalizedTranscript and the supporting helpers normalizeTranscript and isWordBoundaryExtension. runRecognitionCapabilityTests drives the RecordingRecognitionM test newtype through a start, schedule, cancel, stop sequence and asserts that the recorded event log matches the call order exactly. runIntegrateFinalizedTranscriptReducerTests runs the new reducer action through every constructor of TranscriptIntegration — idle no-op, fresh utterance, extension, exact duplicate, earlier snapshot, dedup reset — and confirms that the totals, captions, dedup state, and diagnostic entries all behave the way the legacy build does.

🎭 The Playwright suite stayed exactly as it was. All fifty-one end-to-end tests pass against the new bundle without modification. The existing test hook still exposes simulateFinalTranscript for tests that want to bypass dedup, and slice 9a deliberately did not change that. The whole point of keeping the test hook is to allow the test suite to drive the deterministic path without depending on the browser’s permission UI or microphone access.

🗺️ What Comes Next

🚧 Slice 9b is next. It teaches Main.handleToggle to prefer the on-device path when Chromium exposes the static SpeechRecognition.available() and SpeechRecognition.install() APIs. The user-visible payoff is faster, more private recognition that works without a network connection. The mechanic is a pre-flight check before constructing the recognition instance, and a transparent cloud fallback when the on-device path declines.

🌗 Slice 9c follows. It teaches the orchestrator to retry exactly once on the cloud path when Chromium accepts the on-device pre-flight and then rejects start() at runtime with language-not-supported. The cloudFallbackAttempted flag mentioned in the slice plan lives in the session so it survives across the retry and resets cleanly on the next Toggle-to-start.

🏁 Slice 10 is the cutover, where the legacy word-meter.js bundle finally retires and the PureScript bundle becomes the canonical Word Meter implementation. The path from slice one to slice ten has been long and deliberately small-step, but every step has shipped a user-visible deliverable behind end-to-end tests, and slice 9a is the one where the meter finally counts speech for real.

📚 Book Recommendations

📖 Similar

• Domain Modeling Made Functional by Scott Wlaschin is relevant because the four-constructor TranscriptIntegration sum type in this slice is exactly the kind of make-illegal-states-unrepresentable design Wlaschin advocates, and the chapter on representing decisions as data is essentially what classifyFinalizedTranscript does in twenty lines of code.
• Out of the Tar Pit by Ben Moseley and Peter Marks is relevant because slice 9a is a small case study in the functional core, imperative shell pattern that paper popularized: the recognizer, the timer, and the browser API all live in a thin shell of FFI shims and capability instances, and every decision worth testing lives in the pure core.

↔️ Contrasting

• JavaScript: The Good Parts by Douglas Crockford is relevant because the legacy word-meter.js bundle is exactly the kind of code Crockford was talking about — disciplined imperative JavaScript with carefully chosen idioms — and watching it migrate to a typed pure-functional core is a study in the limits of what discipline alone can buy you.

🔗 Related

• The Elements of Computing Systems by Noam Nisan and Shimon Schocken is relevant because every slice of this port has felt like a layer of the Nand-to-Tetris stack, and slice 9a is the layer where the device drivers finally connect to the application logic.