Iteration functions, which ones do we need?

[Andy Parker]

It has been brought to my attention that there are a number of the functions that were added as part of the "iteration in the puppet language" work that there isn't any kind of general agreement on their value.

I think the list of functions in question is:

  * map

  * reduce

  * filter

  * slice

The use cases for each of these come down to various forms of data manipulation. Map, for instance, can be used to place a prefix or suffix on some, or all of the elements of a list. Filter is used when only a subset of elements is wanted. Slice is to produce groupings of elements in a list. Reduce is the oddest one of the bunch, it is the actual "foreach" loop that everyone is familiar with from languages with mutable variables, but in a very different form.

Are these functions too much? Should they be left out?

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[Trevor Vaughan]

I would like them kept. These are items that I often have to fall back into Ruby to use and it's nice to have them exposed. Otherwise, it's either an inline template or a custom function (doing the exact same thing).

Trevor

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[Erik Dalén]

I don't think they are too much or that any should be left out.

I suppose all of them could be emulated with just the reduce function, so if anything that one should be kept. But it is just cumbersome and makes the code less clear to do a filter in a reduce function.

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Erik Dalén

[Ben Ford]

I don't think we have the luxury of backing them out any more; and to be honest I think that these functions here are mostly OK. Map & filter will be fine. People will struggle with reduce and slice and they probably won't get used much.

I have two real concerns here. Clearly I'm concerned about language complexity, since one of the major questions I get asked in training is why we can't use a case statement inside a resource declaration. My bigger concern, though, is that the question is being asked here, where we're all the top 1% of the top 1%. This is a self-selected list of very advanced users who all find these functions simple and readable. We have needs and requirements that just don't align with the bulk of our userbase.

Ashley said it rather well the other day when he said that having a DSL wasn't a benefit--but having a readable DSL was. The more we add to the language, the less true that becomes, and then there's less of a reason to choose Puppet. I don't want to inhibit the language development, I just want that to be the number one priority in regards to any new functionality and nobody in here, including myself, is really able to identify the end-user impact of these changes.