Scala first program issue

Question

I have just started to learn Scala after some experience with functional programming in other languages.

def freq(c:Char, y:String, list:List[(Char,Int)]): List[(Char,Int)] = list match{
  case _ =>  freq(c, y.filter(_ == c), list :: List((count(c,y),c))) 
  case nil => list
}

In the above code I am getting an error when trying to concatenate the list recursively. The error is occurring in list::List((count(c,y),c)). The count method takes a char and a string and returns an int based on how many times that char occurs.

Any help would be much appreciated. The error I am getting states found [(Char,Int)] required (Char,Int).

Arek · Accepted Answer · 2015-06-22 11:18:00Z

2

Cons operator (::) is an infix operator so if you want to get a type of List[T] and not List[List[T]] then you should write

freq(c, y.filter(_ == c),(count(c,y),c)) :: list)

answered Jun 22, 2015 at 11:18

Arek

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5 Comments

djaidjd Over a year ago

Found (Char,Int) required List[(Char,Int)]??

Arek Over a year ago

In which line? BTW: c is of type Char and a tuple you're creating should have second element of type Int - it still will not compile.

djaidjd Over a year ago

The return type of count is an Int while c is a char.

Arek Over a year ago

So you should write: freq(c, y.filter(_ == c),(c, count(c,y))) :: list)

djaidjd Over a year ago

Like this case _ => freq(c, y.filter(_ == c),(c, count(c,y)) :: list) it compiles :P

Chobeat · Accepted Answer · 2015-06-22 11:17:10Z

0

Also you need to switch the 2 match cases because nil would never be evaluated this way. _ will catch nil too and never continue to reach the second case.

answered Jun 22, 2015 at 11:17

Chobeat

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1 Comment

djaidjd Over a year ago

Thanks I will keep that in mind, it works a little different from Haskell where I can just put [] = [] or otherwise.

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