[Haskell-cafe] Efficient records with arbitrarily many fields [was: Extensible states]

Nikita Volkov nukasu.kanaka at gmail.com
Sat Jul 4 13:45:27 UTC 2015

I somehow missed the preceding discussion, so I'll comment on what I've
seen so far.

> I think the most reasonable default is O(1) for lookup and O(n) for
> extension, like in Nikita Volkov's record package. It is quite unfortunate
> that this package limits the number of fields! If GHC would offer generic
> support for tuples of arbitrary size (with the same efficiency as today)
> this limitation could be avoided and all would be well.

Currently "record" is limited to up to 24 fields. However it was just an
arbitrary number that I've chosen. No part of GHC limits us to that number.
The only reason I'm not introducing bigger arities is that unfortunately
the compilation time of the "record" library grows exponentially in
relation to the highest arity supported. I expect, that limitation could be
lifted once/if the ideas behind the library get implemented as an extension
to GHC.
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