Btukfyl

if this question is stupid, please understand.

I'm starting to learn scala with basic grammar.

But I don't understand why one is error other is not. I tested this with scala worksheet

val range = 1 to 10 by 3 toList

println(s"$range") //error

but the below is the List(actually Seq)

val range = (1 to 10 by 3).toList

println(s"$range") //no problem

I am using intellij 2018.2 ultimate edit.

Edit: Image was changed. I attached capture that is included error message not warning.

Edit: I thought it is intellij version problem, but still doesn't work

If you're getting this error ...

Error:(2, 13) recursive lazy value range needs type

... it's because you're using infix (dot-less) notation where you shouldn't.

Put a blank line before the println(), or a semicolon after the toList and it will work.

The reason for the error is that instance.method(argument) can be turned into ...

instance method argument

... but the compiler is often confused if you try to turn instance.method into ...

instance method

The compiler will look for the missing argument until it hits a semicolon or a blank line.

Either should work. In scala you can omit . with space for method invocation, which is probably broken version of haskell way. I think space is not recommended in scala as per official doc - STYLE GUIDE - METHOD INVOCATION

Example:

scala> val data = "guitar"

data: String = guitar



scala> data.toUpperCase

res8: String = GUITAR

you can use space instead of .,

scala> data toUpperCase

<console>:13: warning: postfix operator toUpperCase should be enabled

by making the implicit value scala.language.postfixOps visible.

This can be achieved by adding the import clause 'import scala.language.postfixOps'

or by setting the compiler option -language:postfixOps.

See the Scaladoc for value scala.language.postfixOps for a discussion

why the feature should be explicitly enabled.

       data toUpperCase

            ^

res9: String = GUITAR

Since .toUpperCase is used after the data-structure without . (it is called postfix Operator) and compiler is simply warning about that. It can be fixed as the warning says,

scala> import scala.language.postfixOps

import scala.language.postfixOps



scala> data toUpperCase

res10: String = GUITAR

Same thing applies to your example. From readability perspective dot makes more readable in your example.

scala> (1 to 10 by 3).toList

res9: List[Int] = List(1, 4, 7, 10)

ALSO, post-fix operators could lead into bugs. For example, 1 + "11" toInt apply the toInt at the end of the computation but maybe what I wanted was 1 + "11".toInt

ALSO, ALSO regarding your bug you need to yell at compiler to stop chaining on toList with ; or a new line after post-fix operator. Or you can use val, def after post-fix operator that way compiler knows it is different context now.

scala> :paste



    import scala.language.postfixOps

    val range = 1 to 10 by 3 toList



    println(s"$range")



// Exiting paste mode, now interpreting.



List(1, 4, 7, 10)

import scala.language.postfixOps

range: List[Int] = List(1, 4, 7, 10)

Also read: Let’s drop postfix operators