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Get vs State
// In the following code, Get is a type which has previously been called State - a name which
// the author found to be confusing, since instances aren't actually states!
//
// Instances are in fact functions which obtain (get) a value that depends on some state.
//
// The following code demonstrates using a Get to set as well as get!
//
// claim: even this is less confusing than using the name State!
//
// N.B. Here, 'State' is the type of the er, state.
object app extends App {
type Get[A, S] = S => (A, S)
case class State(n: Int)
def set(n: Int): State = {
val get = new Get[Unit, State] {
def apply(s0: State) = ((), s0)
}
val (_, s) = get(State(n))
s
}
def get(s0: State): (Int, State) = {
val get = new Get[Int, State] {
def apply(s: State) = (s.n, s)
}
get(s0)
}
// test that get returns the value passed to set
val s0 = set(1)
val (n, s1) = get(s0)
assert(n == 1)
}
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