Provide a Vector datatype

[snoyberg]

In our usage of Fay at FP Complete, we've significantly reduced the occurrences of serialization bugs by using Text in place of String. It also reduces the number of conversions the generated Javascript performs.

I wonder if we could do the same thing with lists and Vectors. A Vector could be represented in server-side code using Data.Vector.Vector, and as an array in generated Javascript. There could be toVector and fromVector helper functions, and serialization would essentially not touch Vector.

However, it also seems like this could be significantly more complicated than the work on Text, since the contained value in Text was always a character, whereas we have full polymorphism with Vectors.

Does this sound like something worth looking into?

[chrisdone]

Hmm I think this would be fine to implement. Could just take the existing list implementation in the FFI and replace the representation (chains of Conses) with a native JS array, add the serialization in Convert (might have to change showToFay to use Data).

I presume any conversion bugs you have had are due to using Automatic and a polymorphically typed String? What is your implementation of Text?

[snoyberg]

One example of a bug we've run into a number of times is #250. We always have to make sure to wrap up our lists in some datatype. We have similar issues with Strings until we switched to Text.

We're using a very simplistic Text implementation provided by yesod-fay: https://github.com/fpco/yesod-fay/blob/master/Language/Fay/Yesod.hs.