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v/examples/lander.v

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// Example of sum types
// Models a landing craft leaving orbit and landing on a world
import rand
import time
struct Moon {
}
struct Mars {
}
fn (m Mars) dust_storm() bool {
return rand.int() >= 0
}
struct Venus {
}
type World = Moon | Mars | Venus
struct Lander {
}
fn (l Lander) deorbit() {
println('leaving orbit')
}
fn (l Lander) open_parachutes(n int) {
println('opening $n parachutes')
}
fn wait() {
println('waiting...')
time.sleep(1)
}
fn (l Lander) land(w World) {
if w is Mars {
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for it.dust_storm() {
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wait()
}
}
l.deorbit()
match w {
Moon {} // no atmosphere
Mars {
// light atmosphere
l.open_parachutes(3)
}
Venus {
// heavy atmosphere
l.open_parachutes(1)
}
}
println('landed')
}
fn main() {
l := Lander {}
l.land(Venus{})
l.land(Mars{})
}