CODEWITHSUNDEEP
scala
Sumit Paliwal
Sumit Paliwal

Reputation: 395

Scala Errors- forward reference extends over definition of value

I am trying to generate the list of intervals which are not included in a given list starting from 1. So I wrote the code as shown below: 

def comparatorInt(first: (Int,Int), second: (Int, Int)) = first._2 <= second._1

val list1 = List((93,97), (5,10),(15,20),(30,50), (76,90)).sortWith(comparatorInt)

var curr = 1
val res = for(x <- list1; tmp = curr; curr = x._2+1) yield(tmp,x._1-1)

Here I am getting an compiler error

Error: forward reference extends over definition of value tmp

lazy val res = for(x <- list1; tmp = curr; curr = x._2+1) yield(tmp,x._1-1)

I am not able to figure out the fix for the issue. Kindly suggest a solution for the same.

Upvotes: 0

Views: 1412

Answers (2)

Dima
Dima

Reputation: 40500

The other answer explains well enough why you are getting the error. I just wanted to add: do not use var, you don't need them most of the time. If you are writing in scala might as well take advantage of the power of the language and stay idiomatic, rather than just writing same old java code with funny syntax :) Consider something like this: 

  ((0,0) :: list1).foldRight(List.empty[(Int,Int)]) { 
     case(x@(a, b), res@((c, d) :: tail)) if(b < c-1) => x :: (b+1, c-1) :: res 
     case(x, res)  => x :: res
  }.tail

(Besides not causing a compilation error, this version also works correctly, unlike yours, that has logical errors ;)).

Upvotes: 1

John K
John K

Reputation: 1285

The curr in the for comprehension is not the same one as your var. What you wrote is equivalent to 

var curr = 1
val res = for(x <- list1; tmp = anotherCurr; anotherCurr = x._2+1) yield(tmp,x._1-1)

so the compiler sees that you are trying to define temp before you defined anotherCurr, hence the error.

If you want to modify the var, you can do it after the yield operation.

Upvotes: 3

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