rose-ash/sx/sx/geography/cek.sx

;; ---------------------------------------------------------------------------
;; CEK Machine — Geography section
;; ---------------------------------------------------------------------------


;; ---------------------------------------------------------------------------
;; Island demos
;; ---------------------------------------------------------------------------

;; Counter: signal + deref in text position
(defisland ~geography/cek/demo-counter (&key initial)
  (let ((count (signal (or initial 0)))
        (doubled (computed (fn () (* 2 (deref count))))))
    (div :class "rounded-lg border border-stone-200 p-4 space-y-2"
      (div :class "flex items-center gap-3"
        (button :class "px-3 py-1 rounded bg-violet-600 text-white text-sm"
          :on-click (fn (e) (swap! count dec)) "-")
        (span :class "text-2xl font-bold text-violet-700 min-w-[3ch] text-center"
          (deref count))
        (button :class "px-3 py-1 rounded bg-violet-600 text-white text-sm"
          :on-click (fn (e) (swap! count inc)) "+"))
      (p :class "text-sm text-stone-500"
        (str "doubled: " (deref doubled))))))

;; Computed chain: base -> doubled -> quadrupled
(defisland ~geography/cek/demo-chain ()
  (let ((base (signal 1))
        (doubled (computed (fn () (* (deref base) 2))))
        (quadrupled (computed (fn () (* (deref doubled) 2)))))
    (div :class "rounded-lg border border-stone-200 p-4 space-y-2"
      (div :class "flex items-center gap-3"
        (button :class "px-3 py-1 rounded bg-violet-600 text-white text-sm"
          :on-click (fn (e) (swap! base dec)) "-")
        (span :class "text-2xl font-bold text-violet-700 min-w-[3ch] text-center"
          (deref base))
        (button :class "px-3 py-1 rounded bg-violet-600 text-white text-sm"
          :on-click (fn (e) (swap! base inc)) "+"))
      (p :class "text-sm text-stone-500"
        (str "doubled: " (deref doubled) "  |  quadrupled: " (deref quadrupled))))))

;; Reactive attribute: (deref sig) in :class position
(defisland ~geography/cek/demo-reactive-attr ()
  (let ((danger (signal false)))
    (div :class "rounded-lg border border-stone-200 p-4 space-y-3"
      (button :class "px-3 py-1 rounded bg-violet-600 text-white text-sm"
        :on-click (fn (e) (swap! danger not))
        (if (deref danger) "Safe mode" "Danger mode"))
      (div :class (str "p-3 rounded font-medium transition-colors "
                       (if (deref danger)
                         "bg-red-100 text-red-800"
                         "bg-green-100 text-green-800"))
        (if (deref danger)
          "DANGER: reactive class binding via CEK"
          "SAFE: reactive class binding via CEK")))))

;; Stopwatch: effect + cleanup
(defisland ~geography/cek/demo-stopwatch ()
  (let ((running (signal false))
        (elapsed (signal 0))
        (time-text (create-text-node "0.0s"))
        (btn-text (create-text-node "Start")))
    (effect (fn ()
      (when (deref running)
        (let ((id (set-interval (fn () (swap! elapsed inc)) 100)))
          (fn () (clear-interval id))))))
    (effect (fn ()
      (let ((e (deref elapsed)))
        (dom-set-text-content time-text
          (str (floor (/ e 10)) "." (mod e 10) "s")))))
    (effect (fn ()
      (dom-set-text-content btn-text
        (if (deref running) "Stop" "Start"))))
    (div :class "rounded-lg border border-stone-200 p-4"
      (div :class "flex items-center gap-3"
        (span :class "text-2xl font-bold text-violet-700 font-mono min-w-[5ch]" time-text)
        (button :class "px-3 py-1 rounded bg-violet-600 text-white text-sm"
          :on-click (fn (e) (swap! running not)) btn-text)
        (button :class "px-3 py-1 rounded bg-stone-400 text-white text-sm"
          :on-click (fn (e) (reset! running false) (reset! elapsed 0)) "Reset")))))

;; Batch: two signals, one notification
(defisland ~geography/cek/demo-batch ()
  (let ((first-sig  (signal 0))
        (second-sig (signal 0))
        (renders    (signal 0)))
    (effect (fn ()
      (deref first-sig) (deref second-sig)
      (swap! renders inc)))
    (div :class "rounded-lg border border-stone-200 p-4 space-y-2"
      (div :class "flex items-center gap-4 text-sm"
        (span (str "first: " (deref first-sig)))
        (span (str "second: " (deref second-sig)))
        (span :class "px-2 py-0.5 rounded bg-green-100 text-green-800 text-xs font-semibold"
          (str "renders: " (deref renders))))
      (div :class "flex items-center gap-2"
        (button :class "px-3 py-1 rounded bg-violet-600 text-white text-sm"
          :on-click (fn (e)
            (batch (fn ()
              (swap! first-sig inc)
              (swap! second-sig inc))))
          "Batch +1")
        (button :class "px-3 py-1 rounded bg-stone-400 text-white text-sm"
          :on-click (fn (e)
            (swap! first-sig inc)
            (swap! second-sig inc))
          "No-batch +1")))))


;; ---------------------------------------------------------------------------
;; Overview page content
;; ---------------------------------------------------------------------------

(defcomp ~geography/cek/cek-content ()
  (~docs/page :title "CEK Machine"

    (~docs/section :title "Three registers" :id "registers"
      (p "The CEK machine makes evaluation explicit. Every step is a pure function from state to state:")
      (ul :class "space-y-1 text-stone-600 list-disc pl-5"
        (li (strong "C") "ontrol — the expression being evaluated")
        (li (strong "E") "nvironment — the bindings in scope")
        (li (strong "K") "ontinuation — what to do with the result"))
      (p "The tree-walk evaluator uses the same three things, but hides them in the call stack. The CEK makes them " (em "data") " — inspectable, serializable, capturable."))

    (~docs/section :title "Why it matters" :id "why"
      (p "Making the continuation explicit enables:")
      (ul :class "space-y-1 text-stone-600 list-disc pl-5"
        (li (strong "Stepping") " — pause evaluation, inspect state, resume")
        (li (strong "Serialization") " — save a computation mid-flight, restore later")
        (li (strong "Delimited continuations") " — " (code "shift") "/" (code "reset") " capture \"the rest of this expression\" as a value")
        (li (strong "Deref-as-shift") " — " (code "(deref sig)") " inside a reactive boundary captures the continuation as the subscriber")))

    (~docs/section :title "Default evaluator" :id "default"
      (p "CEK is the default evaluator on both client (JS) and server (Python). Every " (code "eval-expr") " call goes through " (code "cek-run") ". The tree-walk evaluator is preserved as " (code "_tree_walk_eval_expr") " for test runners that interpret " (code ".sx") " files.")
      (p "The CEK is defined in two spec files:")
      (ul :class "space-y-1 text-stone-600 list-disc pl-5"
        (li (code "frames.sx") " — frame types (IfFrame, ArgFrame, ResetFrame, ReactiveResetFrame, ...)")
        (li (code "cek.sx") " — step function, run loop, special form handlers, continuation operations")))

    (~docs/section :title "Deref as shift" :id "deref-as-shift"
      (p "The reactive payoff. When " (code "(deref sig)") " encounters a signal inside a " (code "reactive-reset") " boundary:")
      (ol :class "space-y-1 text-stone-600 list-decimal pl-5"
        (li (strong "Shift") " — capture all frames between here and the reactive-reset")
        (li (strong "Subscribe") " — register the captured continuation as a signal subscriber")
        (li (strong "Return") " — flow the current signal value through the rest of the expression"))
      (p "When the signal changes, the captured continuation is re-invoked with the new value. The " (code "update-fn") " on the ReactiveResetFrame mutates the DOM. No explicit " (code "effect()") " wrapping needed.")
      (~docs/code :code (highlight
        ";; User writes:\n(div :class (str \"count-\" (deref counter))\n  (str \"Value: \" (deref counter)))\n\n;; CEK sees (deref counter) → signal? → reactive-reset on stack?\n;; Yes: capture (str \"count-\" [HOLE]) as continuation\n;; Register as subscriber. Return current value.\n;; When counter changes: re-invoke continuation → update DOM."
        "lisp")))))


;; ---------------------------------------------------------------------------
;; CEK stepper: interactive stepping debugger
;; ---------------------------------------------------------------------------

(defisland ~geography/cek/demo-stepper (&key initial-expr)
  (let ((source (signal (or initial-expr "(+ 1 (* 2 3))")))
        (state (signal nil))
        (steps (signal 0))
        (history (signal (list)))
        (error-msg (signal nil)))

    ;; Parse and create initial CEK state
    (define start-eval
      (fn ()
        (reset! error-msg nil)
        (reset! history (list))
        (reset! steps 0)
        (let ((parsed (sx-parse (deref source))))
          (if (empty? parsed)
            (reset! error-msg "Parse error: empty expression")
            (reset! state (make-cek-state (first parsed) (make-env) (list)))))))

    ;; Single step
    (define do-step
      (fn ()
        (when (and (deref state) (not (cek-terminal? (deref state))))
          (let ((prev (deref state)))
            (swap! history (fn (h) (append h (list prev))))
            (swap! steps inc)
            (reset! state (cek-step prev))))))

    ;; Run to completion
    (define do-run
      (fn ()
        (when (deref state)
          (let run-loop ((n 0))
            (when (and (not (cek-terminal? (deref state))) (< n 200))
              (do-step)
              (run-loop (+ n 1)))))))

    ;; Reset
    (define do-reset
      (fn ()
        (reset! state nil)
        (reset! steps 0)
        (reset! history (list))
        (reset! error-msg nil)))

    ;; Format control for display
    (define fmt-control
      (fn (s)
        (if (nil? s) "\u2014"
          (let ((c (get s "control")))
            (if (nil? c) "\u2014"
              (sx-serialize c))))))

    ;; Format value
    (define fmt-value
      (fn (s)
        (if (nil? s) "\u2014"
          (let ((v (get s "value")))
            (cond
              (nil? v) "nil"
              (callable? v) (str "\u03bb:" (or (lambda-name v) "fn"))
              :else (sx-serialize v))))))

    ;; Format kont
    (define fmt-kont
      (fn (s)
        (if (nil? s) "\u2014"
          (let ((k (get s "kont")))
            (if (empty? k) "[]"
              (str "[" (join " " (map (fn (f) (get f "type")) k)) "]"))))))

    ;; Initialize on first render
    (start-eval)

    (div :class "space-y-4"
      ;; Input
      (div :class "flex gap-2 items-end"
        (div :class "flex-1"
          (label :class "text-xs text-stone-400 block mb-1" "Expression")
          (input :type "text" :bind source
                 :class "w-full px-3 py-1.5 rounded border border-stone-300 font-mono text-sm focus:outline-none focus:border-violet-400"
                 :on-change (fn (e) (start-eval))))
        (div :class "flex gap-1"
          (button :on-click (fn (e) (start-eval))
                  :class "px-3 py-1.5 rounded bg-stone-200 text-stone-700 text-sm hover:bg-stone-300" "Reset")
          (button :on-click (fn (e) (do-step))
                  :class "px-3 py-1.5 rounded bg-violet-500 text-white text-sm hover:bg-violet-600" "Step")
          (button :on-click (fn (e) (do-run))
                  :class "px-3 py-1.5 rounded bg-violet-700 text-white text-sm hover:bg-violet-800" "Run")))

      ;; Error
      (when (deref error-msg)
        (div :class "text-red-600 text-sm" (deref error-msg)))

      ;; Current state
      (when (deref state)
        (div :class "rounded border border-stone-200 bg-white p-3 font-mono text-sm space-y-1"
          (div :class "flex gap-4"
            (span :class "text-stone-400 w-16" "Step")
            (span :class "font-bold" (deref steps)))
          (div :class "flex gap-4"
            (span :class "text-stone-400 w-16" "Phase")
            (span :class (str "font-bold " (if (= (get (deref state) "phase") "eval") "text-blue-600" "text-green-600"))
              (get (deref state) "phase")))
          (div :class "flex gap-4"
            (span :class "text-violet-500 w-16" "C")
            (span (fmt-control (deref state))))
          (div :class "flex gap-4"
            (span :class "text-amber-600 w-16" "V")
            (span (fmt-value (deref state))))
          (div :class "flex gap-4"
            (span :class "text-emerald-600 w-16" "K")
            (span (fmt-kont (deref state))))
          (when (cek-terminal? (deref state))
            (div :class "mt-2 pt-2 border-t border-stone-200 text-stone-800 font-bold"
              (str "Result: " (sx-serialize (cek-value (deref state))))))))

      ;; Step history
      (when (not (empty? (deref history)))
        (div :class "rounded border border-stone-100 bg-stone-50 p-2"
          (div :class "text-xs text-stone-400 mb-1" "History")
          (div :class "space-y-0.5 font-mono text-xs max-h-48 overflow-y-auto"
            (map-indexed (fn (i s)
              (div :class "flex gap-2 text-stone-500"
                (span :class "text-stone-300 w-6 text-right" (+ i 1))
                (span :class (if (= (get s "phase") "eval") "text-blue-400" "text-green-400") (get s "phase"))
                (span :class "text-violet-400 truncate" (fmt-control s))
                (span :class "text-amber-400" (fmt-value s))
                (span :class "text-emerald-400" (fmt-kont s))))
              (deref history))))))))


;; ---------------------------------------------------------------------------
;; Demo page content
;; ---------------------------------------------------------------------------

(defcomp ~geography/cek/cek-demo-content ()
  (~docs/page :title "CEK Demo"

    (~docs/section :title "What this demonstrates" :id "what"
      (p "These are " (strong "live islands") " evaluated by the CEK machine. Every " (code "eval-expr") " goes through " (code "cek-run") ". Every " (code "(deref sig)") " in an island creates a reactive DOM binding via continuation frames.")
      (p "The CEK machine is defined in " (code "cek.sx") " and " (code "frames.sx") " — pure s-expressions, bootstrapped to both JavaScript and Python."))

    (~docs/section :title "Stepper" :id "stepper"
      (p "The CEK machine is pure data\u2192data. Each step takes a state dict and returns a new one. "
         "Type an expression, click Step to advance one CEK transition.")
      (~geography/cek/demo-stepper :initial-expr "(let ((x 10)) (+ x (* 2 3)))")
      (~docs/code :code (highlight
        "(defisland ~demo-stepper (&key initial-expr)\n  (let ((source (signal (or initial-expr \"(+ 1 2)\")))\n        (state (signal nil))\n        (steps (signal 0))\n        (history (signal (list))))\n    ;; Parse and create initial CEK state\n    (define start-eval (fn ()\n      (let ((parsed (sx-parse (deref source))))\n        (reset! state (make-cek-state (first parsed) (make-env) (list))))))\n    ;; Single step\n    (define do-step (fn ()\n      (when (and (deref state) (not (cek-terminal? (deref state))))\n        (swap! history (fn (h) (append h (list (deref state)))))\n        (swap! steps inc)\n        (reset! state (cek-step (deref state))))))\n    (start-eval)\n    (div\n      (input :type \"text\" :bind source :on-change (fn (e) (start-eval)))\n      (button :on-click (fn (e) (do-step)) \"Step\")\n      ;; Display C, V, K registers from (deref state)\n      (pre (str \"C: \" (sx-serialize (get (deref state) \"control\")))))))"
        "lisp")))

    (~docs/section :title "1. Counter" :id "demo-counter"
      (p (code "(deref count)") " in text position creates a reactive text node. " (code "(deref doubled)") " is a computed that updates when count changes.")
      (~geography/cek/demo-counter :initial 0)
      (~docs/code :code (highlight
        "(defisland ~demo-counter (&key initial)\n  (let ((count (signal (or initial 0)))\n        (doubled (computed (fn () (* 2 (deref count))))))\n    (div\n      (button :on-click (fn (e) (swap! count dec)) \"-\")\n      (span (deref count))\n      (button :on-click (fn (e) (swap! count inc)) \"+\")\n      (p (str \"doubled: \" (deref doubled))))))"
        "lisp")))

    (~docs/section :title "2. Computed chain" :id "demo-chain"
      (p "Three levels of computed: base -> doubled -> quadrupled. Change base, all propagate.")
      (~geography/cek/demo-chain)
      (~docs/code :code (highlight
        "(let ((base (signal 1))\n      (doubled (computed (fn () (* (deref base) 2))))\n      (quadrupled (computed (fn () (* (deref doubled) 2)))))\n  (span (deref base))\n  (p (str \"doubled: \" (deref doubled)\n         \"  |  quadrupled: \" (deref quadrupled))))"
        "lisp")))

    (~docs/section :title "3. Reactive attributes" :id "demo-attr"
      (p (code "(deref sig)") " in " (code ":class") " position. The CEK evaluates the " (code "str") " expression, and when the signal changes, the continuation re-evaluates and updates the attribute.")
      (~geography/cek/demo-reactive-attr)
      (~docs/code :code (highlight
        "(div :class (str \"p-3 rounded font-medium \"\n             (if (deref danger)\n               \"bg-red-100 text-red-800\"\n               \"bg-green-100 text-green-800\"))\n  (if (deref danger) \"DANGER\" \"SAFE\"))"
        "lisp")))

    (~docs/section :title "4. Effect + cleanup" :id "demo-stopwatch"
      (p "Effects still work through CEK. This stopwatch uses " (code "effect") " with cleanup — toggling the signal clears the interval.")
      (~geography/cek/demo-stopwatch)
      (~docs/code :code (highlight
        "(effect (fn ()\n  (when (deref running)\n    (let ((id (set-interval (fn () (swap! elapsed inc)) 100)))\n      (fn () (clear-interval id))))))"
        "lisp")))

    (~docs/section :title "5. Batch coalescing" :id "demo-batch"
      (p "Two signals updated in " (code "batch") " — one notification cycle. Compare render counts between batch and no-batch.")
      (~geography/cek/demo-batch)
      (~docs/code :code (highlight
        "(batch (fn ()\n  (swap! first-sig inc)\n  (swap! second-sig inc)))\n;; One render pass, not two."
        "lisp")))))