CODEWITHSUNDEEP
alloy
Roger Costello
Roger Costello

Reputation: 3209

How to implement order in a set of sets?

When an aircraft approaches an airport to land, the aircraft's approach procedure is divided up into transitions. Each transition consists of a set of legs. 

sig Transition {
     legs: set Leg 
}
sig Leg {}

The set of legs within a transition is ordered. For each transition, I want to be able to access the first leg in the transition, the last leg in the transition, and I want to navigate from leg to leg in the transition. Thus, I want a first, last, and next function.

What's the simplest way to implement this? I have an implementation working but I wonder if there's something simpler. My implementation associates each Leg to a sequence number:

open util/ordering [SequenceNumber]
sig SequenceNumber {}

sig Transition {
     legs: Leg one -> one SequenceNumber
}

Then I created my own utility functions:

fun First (t: Transition): Leg {
    t.legs.(min [Leg.(t.legs)])
}

fun Last (t: Transition): Leg {
    t.legs.(max [Leg.(t.legs)])
}

fun Next (t: Transition, leg: Leg): Leg { 
    t.legs.(next [leg.(t.legs)])
}

I am hoping you can show me a simpler solution.

Upvotes: 0

Views: 88

Answers (1)

user1513683
user1513683

Reputation: 419

Why not use seq Leg and the inbuilt sequence predicates & functions?

Upvotes: 1

Related Questions