Higher Order Functions

[wdonne]

I've been writing functions in jslt and I miss higher order functions. Being able to pass a function as an argument to another function or to return a function can make code a lot DRYer. I think closures would be a vital part of this feature.

[larsga]

I have a lot of sympathy for this view, and have been thinking along the same lines myself. The difficulty is that so far JSLT has maintained a strict "all values are JSON" approach, which makes functions-as-values problematic. Although not necessarily impossible.

It would be interesting to see some code examples showing ways you are thinking you would use this feature, assuming JSLT had it.

[wdonne]

I understand that the impact would be considerable in that case. Because I changed my original code in the end the better example is gone now. Instead I'll show this tiny one. The current code is this:

def relation(filteredRelations)
  if (size($filteredRelations) == 1) $filteredRelations[0] else null

def relation-parent(relations, type)
  relation([for ($relations) . if (.type == 1 and .pupilRelationType == $type)])

def relation-self(relations)
  relation([for ($relations) . if (.type == 1 and .pupilRelationType == null)])

The "algorithm" is repeated in the functions relation-parent and relation-self. Instead it could be like this:

def relation-with(relations, criterion)
    relation([for ($relations) . if (.type == 1 and criterion(.))])

It could then be called like this:

relation-with(relations, json -> json.pupilRelationType == null)

The example is too small to make a point, but for every new criterion I would have to repeat relation-with, while with a predicate I could use any criterion.