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Editorial Team
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Asked: 2026-06-12T23:00:42+00:00

Can anyone explain why I see this compile error for the following when I

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Can anyone explain why I see this compile error for the following when I omit the dot notation for applying the foldLeft function?(version 2.9.2) 

scala> val l = List(1, 2, 3)
res19: List[Int] = List(1 ,2 ,3)

scala> l foldLeft(1)(_ * _)
<console>:9: error: Int(1) does not take parameters
                    l foldLeft(1)(_ * _)
                                    ^

but

scala> l.foldLeft(1)(_ * _) 
res27: Int = 6

This doesn’t hold true for other higher order functions such as map which doesn’t seem to care whether I supply the dot or not.

I don’t think its an associativity thing because I can’t just invoke foldLeft(1)

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1 Answer

  1. Editorial Team

    It’s because foldLeft is curried. As well as using the dot notation, you can also fix this by adding parentheses:

    scala> (l foldLeft 1)(_ * _)
res3: Int = 6

    Oh – and regarding your comment about not being able to invoke foldLeft(l), you can, but you need to partially apply it like this:

    scala> (l foldLeft 1) _
res3: ((Int, Int) => Int) => Int = <function1>
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