[Haskell-cafe] Read lines of a file into a Vector

Jake jake.waksbaum at gmail.com
Thu Aug 11 07:03:55 UTC 2016

I want to write a function that will read the contents of a file and return
a Vector of its lines:

readLines :: Handle -> IO (Vector String)

I have an implementation that works but seems to naive and inefficient to
me because it reads the entire file contents, *then *splits it into lines,
and *then* converts it to a Vector from a list.

readLines h = fromList . lines <$> hGetContents h

I would like to a) use hGetLine and continue until I get an isEOFError and
b) read directly into a Vector instead of a list. I started something using
Data.Vector.unfoldr but I the presence of the IO monad around my String was
causing issues I couldn't figure out how to solve.

I'd also be curious to see how to do either one of these things separately
and I assume they'd each help make my program more efficient on their own.
Or, maybe my implementation is not as terrible as I thought because some
laziness/fusion/optimization magic is happening behind the scenes?

Jake Waksbaum
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