function retrieveRelated($productName)
{
return S::of(function (Cacher $cache) use($productName) {
// do some database work
$products = ['iPhone 5', 'iPhone 6s'];
return [$products, $cache->put($productName, $products)];
});
}
/**
* ioState :: IO a -> State IO a
*
* @param M\IO $io
*
* @return M\State
*/
function ioState(M\IO $io)
{
return M\State::of(function ($state) use($io) {
list($key, $data) = $state;
$value = $io->run();
$data[$key] = $value;
$newState = [$key, $data];
return [$value, $newState];
});
}
/**
* modify :: State s m => (s -> s) -> m ()
*
* Monadic state transformer.
*
* Maps an old state to a new state inside a state monad.
* The old state is thrown away.
*
* @param callable $transformation
*
* @return M\State
*/
function modify(callable $transformation)
{
return M\State::of(function ($state) use($transformation) {
return [null, $transformation($state)];
});
}
