Improve document on unsafeTextWithLength

Author: reixn

prettyprinter/src/Prettyprinter/Internal.hs

@@ -27,7 +27,7 @@ module Prettyprinter.Internal (
     emptyDoc, nest, line, line', softline, softline', hardline,
 
     -- ** create doc directly from Text, unsafe
-    unsafeTextWithLength
+    unsafeTextWithLength,
 
     -- ** Primitives for alternative layouts
     group, flatAlt,
@@ -455,11 +455,6 @@ instance Pretty a => Pretty (Maybe a) where
 -- Manually use @'hardline'@ if you /definitely/ want newlines.
 instance Pretty Text where pretty = vsep . map unsafeTextWithoutNewlines . T.splitOn "\n"
 
--- | Convert text to Doc. Must not contain newlines. 
--- Useful when dealing with wide characters and emojis
-unsafeTextWithLength :: Text -> Int -> Doc ann
-unsafeTextWithLength txt l = Text l txt
-
 -- | (lazy 'Text' instance, identical to the strict version)
 instance Pretty Lazy.Text where pretty = pretty . Lazy.toStrict
 #endif
@@ -484,6 +479,20 @@ unsafeTextWithoutNewlines text = case T.uncons text of
         | T.null ext -> Char t
         | otherwise -> Text (T.length text) text
 
+-- | @(unsafeTextWithLength t l)@ convert text @t@ of length @l@ into Doc.
+-- 
+-- The string must not contain any newline characters.
+--
+-- The real length can be specified manually when there are some wide character 
+-- or emojis in the string, so that it can be layed out correctly.
+--
+-- For example using doclayout to get the real length
+-- @
+--      unsafeTextWithLength "😃" (realLength "😃")
+-- @
+unsafeTextWithLength :: Text -> Int -> Doc ann
+unsafeTextWithLength txt l = Text l txt
+
 -- | The empty document behaves like @('pretty' "")@, so it has a height of 1.
 -- This may lead to surprising behaviour if we expect it to bear no weight
 -- inside e.g. 'vcat', where we get an empty line of output from it ('parens'