`fsep` and `fcat` are confusing as well. Does anyone know what "Paragraph fill" mean in this context?

[jwaldmann]

fsep and fcat are confusing as well. Does anyone know what "Paragraph fill" mean in this context?

"Paragraph fill" version of sep.

"Paragraph fill" version of cat.

Originally posted by @banacorn in https://github.com/haskell/pretty/issues/48#issuecomment-793432598

[jwaldmann]

I agree this is under-documented. There is no mention of "paragraph fill" in the original paper? http://belle.sourceforge.net/doc/hughes95design.pdf

From experimentation, the semantics of fcat/fsep seems to be

• if each element is one-line: fill up current line (with hcat or hsep) until ribbon width, then insert line break and repeat
• else, vcat

There's a specification in the code https://hackage.haskell.org/package/pretty-1.1.3.6/docs/src/Text.PrettyPrint.Annotated.HughesPJ.html#fsep

Perhaps something (from that spec, or from my comment here) could be lifted to API doc.