counter.afs

// SPDX-License-Identifier: MPL-2.0
// SPDX-FileCopyrightText: 2025-2026 hyperpolymath
//
// AffineScript TEA counter — Stage 3c dogfood
//
// Demonstrates The Elm Architecture in AffineScript:
//   - Model is an owned value: each update consumes the old model, produces a new one
//   - Msg is linear: consumed by update, not reusable
//   - Cmd carries obligations: None means no side-effects, Log carries a message to handle
//
// Run: affinescript eval examples/counter.afs
//   At the stdin prompt, type one of: Increment  Decrement  Reset
//   Ctrl-D (EOF) exits cleanly.

// ── Msg ─────────────────────────────────────────────────────────────────────
// Linear: each message is consumed exactly once by update.

enum CounterMsg {
  Increment,
  Decrement,
  Reset
}

// ── Cmd ─────────────────────────────────────────────────────────────────────
// Linear obligation.  None → no effect.  Log(String) → something to handle.
// Dropping a non-None Cmd at compile time is a quantity violation (Stage 1).

enum CounterCmd {
  None,
  Log(String)
}

// ── init ─────────────────────────────────────────────────────────────────────
// Produces the initial model.  No commands needed at start-up.

fn counter_init() -> Int {
  0
}

// ── update ───────────────────────────────────────────────────────────────────
// Consumes Msg and old Model; produces new Model plus any commands.
// The old model is gone after this call — AffineScript enforces this via QTT.

fn counter_update(msg: CounterMsg, model: Int) -> Int {
  match msg {
    Increment => model + 1,
    Decrement => model - 1,
    Reset     => 0
  }
}

// ── view ─────────────────────────────────────────────────────────────────────
// Borrows the model (read-only), renders a string.
// Rebuilding the view does not consume the model.

fn counter_view(model: Int) -> String {
  "Count: " ++ int_to_string(model)
}

// ── subscriptions ────────────────────────────────────────────────────────────
// No real-time subscriptions at the interpreter level.

fn counter_subs(model: Int) -> String {
  "None"
}

// ── main ─────────────────────────────────────────────────────────────────────
// Wire up the TEA runtime and hand off to the interpreter loop.

fn main() -> () {
  tea_run({
    init:          counter_init,
    update:        counter_update,
    view:          counter_view,
    subscriptions: counter_subs
  })
}