Maxim Grishin - Scala test tasks #1
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| class Assignment1 { | ||
| // Fibonacci sequence | ||
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| def fib(n: Int) = fibHelper(0, n, 0, 1) |
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Solution is good! But it is possible to improve style. You can use pattern matching instead of if. You can move n: Int to be the first argument and set default values for other arguments, so we can call fibHelper like that: fibHelper(n)
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| // Prime numbers | ||
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| def prime(n: Int): Int = primeHelper(n, 0, 1) |
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Cool! Same comments on style as for fib. You can improve code with Sieve of Eratosthenes and there is a really functional implementation using that approach, it involves usage of Stream since scala affords
infinite lists through Stream
| // High order functions - 2 - map | ||
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| def map[A, B](f: A => B, l: List[A]): List[B] = l match { | ||
| case head :: tail => List[B](f(head)) ::: map(f, tail) |
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I think it is more efficient to just do f(head) :: map(f, tail) because concatenation ::: requires whole list traversal
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| def map[A, B](f: A => B, l: List[A]): List[B] = l match { | ||
| case head :: tail => List[B](f(head)) ::: map(f, tail) | ||
| case Nil => List[B]() |
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Lists constructed as:
Nil or el :: List
so you can return just Nil instead of ListB
| // High order functions - 5 - filter and map revisited | ||
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| def foldMap[A, B](f: A => B, l: List[A]): List[B] = | ||
| foldLeft(List[B](), (b: List[B], a: A) => b ::: List[B](f(a)), l) |
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You also can pass Nil as an acc. Also you can consider f(a) :: b instead of b ::: List[B](f(a)), but in this case you should reverse list at the end
| case object Zero extends Nat | ||
| case class Succ(n: Nat) extends Nat | ||
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| def add(a: Nat, b: Nat): Nat = (a, b) match { |
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It is possible to define this function with two cases too (as sub)
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