More functional approach

Question

I wonder if there is a more "functional" way of implementing something like this:

@months.zipWithIndex.foreach { case (month, index) =>
    if (index%3 == 0) {
        <tr>
    }
    <td>@month</td>
    if (index%3 == 0) {
        </tr>
    }
}

Can these two if-statements be removed by using something other than foreach?

Answer 1

I am not sure which framework you are using, but this is how you could do it using Scala´s native XML library:

 <div>
 { for (row <- months grouped 3) yield (<tr> { for (month <- row) yield (<td> {month} </td>) } </tr>) }
 </div>

Rendered slightly more prettily, the code looks like this:

for (row <- months grouped 3) yield {
  <tr> 
  { for (month <- row) yield (<td> {month} </td>) }
  </tr>
}

Which hopefully makes the structure clear.

If your framework works with yield, all you need to do is add @ in the appropriate places. If it does not, you might have to do something like this:

for (row <- @months grouped 3) {
  <tr>
  for (month <- @row) {
    <td> @month </td>
  }
  </tr>
}

Your code is structured only around months, so has to use conditional logic to create your rows. My code is structured around rows (and within that around months), so needs no conditionals. My code also only has the value for the number of months in one place, which is less error prone and makes it easier to change the number of months in a row.

You don't have to use a list comprehension, though. The important thing is simply to slice the list up into groups of 3 (or n, where n is the number of months you want in each row) and iterate over those.

Answer 2

I don't believe there's any kind of functional looping structure that will allow you to obtain this behavior without the 'if' statements. The fact is, you have to include something conditionally, and so you have to check that condition somehow. This is a bit more idiomatic way to do it, I believe, and I think it's prettier:

@months.zipWithIndex.foreach { 
    case (month, index) if (index % 3 == 0) => <tr><td>@month</td></tr>
    case (month, _) => <td>@month</td>
}

I'm guessing you're using Play or something like that based on the @months. I've never used Play much so I'm not sure what the return type needs to be for a function like this but it might be possible to do something along the lines of

@months.zipWithIndex.foreach { case (month, index) => 
    @str = <td>@month</td>
    if(index % 3 == 0) @str = "<tr>" + @str + "<\tr>"
    @str
}

but I don't personally think that's helping anything. Hope that was helpful.