Can I create a tuple from a non-comma separated set of tokens in Scala?

Question

I'm continuing my Stack-Overflow-Driven Programming of a testing DSL - thanks to all who have contributed so far!

At the moment my DSL reads like this

scenario("Incorrect password") {
  given("user visits", the[AdminHomePage])
  then(the[SignInPage], "is displayed")      

  when("username", "admin", "and password", "wrongpassword", "are entered")
  then(the[SignInPage], "is displayed")      
  and("Error message is", "Sign in failed")
}

given, when and then are methods that take Any, so when called like this they are passed a tuple of the arguments - Why and how is Scala treating a tuple specially when calling a one arg function? .

Ideally I'd drop the commas, so that it reads much nicer, with just spaces separating the tokens

scenario("Incorrect password") {
  given("user visits" the[AdminHomePage])
  then(the[SignInPage] "is displayed")      

  when("username" "admin" "and password" "wrongpassword" "are entered")
  then(the[SignInPage] "is displayed")      
  and("Error message is" "Sign in failed")
}

Can anyone think of any technique that would let me achieve this goal, or is it going too far for an internal DSL?

score 1 · Answer 1 · answered Jun 10 '11 at 10:54

1

No, you can't create tuples from space separated tokens (although you can use a custom operator as separator instead of comma). What you can do is to use the dot free syntax like this:

obj method obj method obj ...

Many DSL implementations (like specs) utilize this syntax to create more "text-like" syntax.

answered Jun 10 '11 at 10:54

Jesper Nordenberg

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I was wondering if that was a path, but every other token would have to be the name of a method? – Duncan McGregor Jun 10 '11 at 10:58
Yes, so you can add "extension methods" to the String type, but the method names themselves can't be strings, for example: `"hello" is "displayed" and "groovy"` – Jesper Nordenberg Jun 10 '11 at 14:06

score 1 · Accepted Answer · answered Jun 10 '11 at 11:39

1

You need a method/operator between the "tokens". For pairs there is already ->, e.g.

println("hello" -> 12 -> '!' -> 12.0)
//--> (((hello,12),!),12.0)

answered Jun 10 '11 at 11:39

Landei

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I did consider using | or something like that, but everything seems as least as obtrusive as the the commas, for a lot more work. – Duncan McGregor Jun 10 '11 at 11:57
1

Often "is" seems to work well in your case: `then(the[SignInPage] is "displayed")`, `and("ErrorMessage" is "Sign in failed")` – Landei Jun 10 '11 at 12:39

score 1 · Answer 3 · answered Jun 10 '11 at 11:49

1

Not sure if it works:

As mentioned before you can call one argument methods in operator notation. There is also the Dynamic Trait which allows dynamic invocation of methods: http://www.scala-lang.org/api/current/index.html#scala.Dynamic

So if you start with an object implementing the dynamic trait it might work ..

answered Jun 10 '11 at 11:49

Jens Schauder

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But I'd still need every other token to be interpretable as a method name...? – Duncan McGregor Jun 10 '11 at 11:58
it would be interpreted as a method name, but the method wouldn't need to exist. – Jens Schauder Jun 10 '11 at 12:01
Indeed, but that means no spaces, can't just use strings etc – Duncan McGregor Jun 10 '11 at 12:17

Can I create a tuple from a non-comma separated set of tokens in Scala?

3 Answers3