List equality using parser combinators

Question

I've grabbed some Scala CSV parsing code from here:

Use Scala parser combinator to parse CSV files

And then I tried to write a basic test for it:

assertEquals(List(List()), CSV.parse(""))

And this fails, with message:

java.lang.AssertionError: expected: scala.collection.immutable.$colon$colon but was: scala.collection.immutable.$colon$colon

Any ideas? The output from CSV.parse is an empty List[List[String]] but seems to have a different hashCode than List(Nil) or ListList[String] etc. I can't seem to find any way to compose a list which is equal to the output of CSV.parse("").

UPDATE:

Here is the failure using REPL:

scala> assertEquals(List(Nil), CSV.parse("")) 
java.lang.AssertionError: expected: scala.collection.immutable.$colon$colon<List(List())> but was: scala.collection.immutable.$colon$colon<List(List())>

paradigmatic · Accepted Answer · 2011-07-13 16:24:30Z

2

Edited: I tried the parser you supplied in the link:

scala> CSV.parse("")
res7: List[List[String]] = List(List(""))

So apparently, it doesn't return a List with an empty List, but a List with a List with the empty string. So your test should fail.

edited Jul 13, 2011 at 16:24

answered Jul 13, 2011 at 15:50

paradigmatic

40.5k18 gold badges92 silver badges148 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

waterlooalex Over a year ago

Good catch, thanks, thats it. What confused me is that println(List(List("")) and println(List[List[String]](Nil)) have the same output, so in my println calls, and in the JUnit failures I seemed to be getting the same values on either side.

waterlooalex Over a year ago

I don't (yet) understand how/why the REPL shows different output than toString.

Collectives™ on Stack Overflow

List equality using parser combinators

1 Answer 1

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related