Counter API

A simple counter with increment, decrement, and get. Demonstrates memory slots and basic state management. Serve: soma serve 049_counter_api.cell Test: curl localhost:8080/increment/5 curl localhost:8080/get

Example 049 of the basic Soma programs: a small, commented program that teaches one thing. Every output below was printed by soma 3.2.4 when this page was built.

How it is built

The cell CounterAPI declares 5 signals in its face: increment(amount: Int) -> Int, decrement(amount: Int) -> Int, get() -> Int, reset() -> Int and demo() -> String; keeps 1 memory slot: value (Map<String, Int>, persistent and consistent). Handlers: increment (line 31), decrement (line 38), get (line 45), reset (line 49) and demo (line 54).

Generated from soma describe on this file.

The source

049_counter_api.cell

// ============================================================================
// 049 — Counter API
// ============================================================================
// A simple counter with increment, decrement, and get.
// Demonstrates memory slots and basic state management.
//
// Serve: soma serve 049_counter_api.cell
// Test:  curl localhost:8080/increment/5
//        curl localhost:8080/get
//
// Run:   soma run 049_counter_api.cell demo
// Expect:
//   Initial: 0
//   After +5: 5
//   After +3: 8
//   After -2: 6

cell CounterAPI {
    face {
        signal increment(amount: Int) -> Int
        signal decrement(amount: Int) -> Int
        signal get() -> Int
        signal reset() -> Int
        signal demo() -> String
    }

    memory {
        value: Map<String, Int> [persistent, consistent]
    }

    on increment(amount: Int) {
        let current = value.get("count") ?? 0
        let new_val = current + amount
        value.set("count", new_val)
        return new_val
    }

    on decrement(amount: Int) {
        let current = value.get("count") ?? 0
        let new_val = current - amount
        value.set("count", new_val)
        return new_val
    }

    on get() {
        return value.get("count") ?? 0
    }

    on reset() {
        value.set("count", 0)
        return 0
    }

    on demo() {
        reset()
        let v0 = get()
        print("Initial: {v0}")

        increment(5)
        let v1 = get()
        print("After +5: {v1}")

        increment(3)
        let v2 = get()
        print("After +3: {v2}")

        decrement(2)
        let v3 = get()
        print("After -2: {v3}")

        return "done"
    }
}

What the toolchain says

$ soma check 049_counter_api.cell
✓ All checks passed.

$ soma run 049_counter_api.cell demo
Initial: 0
After +5: 5
After +3: 8
After -2: 6
done