Added toLines.

[GregorySchwartz]

Resolves #354. Probably needs a better name, should avoid partial functions, and needs verification if bang patterns are needed, especially on stream.

[Gabriella439]

@GregorySchwartz: If you don't mind, I put up an alternative fix here: #356

The main reason for doing it the other way was to ensure that toLines can handle infinite streams and operate in constant space when possible

[GregorySchwartz]

For educational purposes, is the constant space due to the strict pair?

[Gabriella439]

@GregorySchwartz: The main difference is that in the streaming version the outer step' function immediately passes each complete Line to the inner step function here:

-- Emit each complete `Line`
x' <- foldM step x (NonEmpty.init lines')

... before moving on to the next Text chunk. In particular, the streaming version does not store the complete sequence of Lines inside of the accumulator as a Shell Line.

Passing completed Lines to the inner step function immediately instead of holding onto them ensures that even if there are a large (or infinite) number of output Lines then the toLines function still makes progress and doesn't wait until computing all of the Lines to begin forwarding them downstream.

[GregorySchwartz]

Ah, I never thought of building a Shell outside of fold or reduce, so that makes sense.

[Gabriella439]

I'll go ahead and merge #356, then. However, I'd still like you to review #357 if you can to see if it addresses your use case before merging that one