unsafeTextWithoutNewlines might be slower than necessary

[sjakobi]

prettyprinter/prettyprinter/src/Prettyprinter/Internal.hs

Lines 468 to 477 in 0dbe08f

	-- | @(unsafeTextWithoutNewlines s)@ contains the literal string @s@.
	--
	-- The string must not contain any newline characters, since this is an
	-- invariant of the 'Text' constructor.
	unsafeTextWithoutNewlines :: Text -> Doc ann
	unsafeTextWithoutNewlines text = case T.uncons text of
	Nothing -> Empty
	Just (t,ext)
	| T.null ext -> Char t
	| otherwise -> Text (T.length text) text

It seems that this function would allocate a new Text value in order to perform the T.null check on it. GHC may be able to optimize this allocation away, but it seems fragile.

[sjakobi]

Apparently this issue was investigated before: https://github.com/quchen/prettyprinter/blob/0dbe08f65468697b729d5e05c98c89a58a42486b/prettyprinter/bench/FasterUnsafeText.hs