- List is immutable, its elements can’t be changed
- List is recursive
- All the elements of list have the same type
- All lists are constructed from
- An empty list Nil
- Operator cons (::)
- Operators ending with “:” is calculated from right to left
A :: B :: C is interpreted A :: (B :: C)
Functions on list
- Implement of last
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def last[T](xs: List[T]): T = xs match { case List() => throw new Error("Empty list") case List(x) => x case y :: ys => last(ys) } |
- Implement of init
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def init[T](xs: List[T]): List[T] = xs match { case List() => throw new Error("init of empty list") case List(_) => List() case y :: ys => y :: init(ys) } |
- Implement of concat
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def concat[T](xs: List[T], ys: List[T]): List[T] = xs match { case List() => ys case z :: zs => z :: concat(zs, ys) } |
- Implement of reverse
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def reverse[T](xs: List[T]): List[T] = xs match { case List() => List() case y :: ys => reverse(ys) ::: List(y) } |
- Implement of removeAt
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def removeAt[T](xs: List[T], n: Int): List[T] = { if(n < 0 || n > xs.length - 1) throw new Error("Can't remove") var count = n xs match { case y :: ys => if(count == 0) ys else { count = count - 1 y :: removeAt(ys, count) } } } |
List patterns
- Nil: an empty list
- p :: ps: this pattern will match any lists whose head matches p and tail matches ps
- List(p1, …, pn) is the same as p1 :: … :: pn :: Nil
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