Callback Algorithms example

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// Build from the repository root:
// build/flecha build examples/callback_algorithms.fl \
//     --lib std=std/src -o /tmp/flecha-callback-algorithms
// Returns 42 after exercising every v0.2.0 callback form.

module callback_algorithms;

@imports
    :: lib::std::containers::collections;

bool is_greater_than_two(&const i32 value) {
    return *value > 2;
}

i32 main() {
    [4]i32 values = [1, 2, 3, 4];

    // Named function.
    index, found :=
        collections::find_if<i32>(values[:], is_greater_than_two);
    if !found or index != 2 {
        return 1;
    }

    // Captureless, contextually inferred anonymous function.
    total := collections::fold<i32, i32>(
        values[:],
        0,
        (sum, value) => { return sum + *value; }
    );
    if total != 10 {
        return 2;
    }

    // Capturing anonymous function.
    i32 visited = 0;
    collections::for_each<i32>(values[:], [&visited](value) => {
        visited = visited + *value;
    });
    if visited != 10 {
        return 3;
    }

    // Captureless comparator.
    collections::sort_by<i32>(values[:], (left, right) => {
        return *left > *right;
    });
    if values[0] != 4 or values[1] != 3 or
        values[2] != 2 or values[3] != 1 {
        return 4;
    }

    return 42;
}