$ package:ghc

Concatenate with an optional newline

Join two docs together vertically. If there is no vertical overlap it "dovetails" the two onto one line.

Join two SDoc together vertically

Above, except that if the last line of the first argument stops at least one position before the first line of the second begins, these two lines are overlapped. For example:

text "hi" $$ nest 5 (text "there")

lays out as

hi   there

rather than

hi
there

$$ is associative, with identity empty, and also satisfies

• (x $$ y) <> z = x $$ (y <> z), if y non-empty.

Above, with no overlapping. $+$ is associative, with identity empty.