Re: What do you assume when you see fromListN in a library?

I should add that one of my actual use cases is to take a list of unknown length and chunk it into a list of fixed sized vectors. I use fromListN which allows me to fill a vector up until N and then I move onto the next one etc until the list is exhausted. Requiring an exact N is a pessimisation for me because it would force me to create intermediate lists of the desired size before calling fromListN. I do not mind if a function with the current behaviour exists but with a different name like fromListUntilN or something similar. On Fri, 28 Feb 2020 at 16:58, John Ky wrote:

I expect it to pre-allocate space for N elements and populate the vector until there are no more elements or the vector is full and return a vector that has a size the minimum of the length of the input list and N.

To me size hint is definitely not what I want because it hides performance/allocation bugs.

If it is possible to modify the function type then I would have it return a tuple of a vector with maximum size N as well as the remainder of the list.

On Fri, 28 Feb 2020, 2:41 pm Zemyla, wrote:

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I'm kind of the opposite. I think the number given to fromListN should be a "size hint", not a redundant coding of the size of the list given.

On Thu, Feb 27, 2020, 21:31 chessai . wrote:

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I expect a list with precisely length N, and reject anything else. IIRC both primitive and vector do this

On Thu, Feb 27, 2020, 6:54 PM Carter Schonwald < carter.schonwald@gmail.com> wrote:

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Hey everyone: When you see fromListN as a function in a library, do you assume / presume it’s expecting an exactly N element list ? Or do you expect/tolerate other behavior ?

Should it reject shorter lists?

Should it truncate or reject longer lists?

A corner case of this came up in some bug discussion I was having regarding vector, and I shall claim and or presume that most folks assume exact size with prompt rejection of too long or too short.

Thoughts please ?

-Carter _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

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