-- |
-- Module : Text.PrettyPrint.HughesPJ
-- Copyright : (c) The University of Glasgow 2001
--- License : BSD-style (see the file libraries/core/LICENSE)
+-- License : BSD-style (see the file libraries/base/LICENSE)
--
-- Maintainer : libraries@haskell.org
-- Stability : provisional
-- Portability : portable
--
--- John Hughes\'s and Simon Peyton Jones\'s Pretty Printer Combinators
+-- John Hughes's and Simon Peyton Jones's Pretty Printer Combinators
--
-- Based on /The Design of a Pretty-printing Library/
-- in Advanced Functional Programming,
nest k empty = empty
which wasn't true before.
- * Fixed an obscure bug in sep that occassionally gave very wierd behaviour
+ * Fixed an obscure bug in sep that occassionally gave very weird behaviour
* Added $+$
It is Really Useful in practice.
2. There is a paragraph-fill combinator, fsep, that's much like sep,
- only it keeps fitting things on one line until itc can't fit any more.
+ only it keeps fitting things on one line until it can't fit any more.
3. Some random useful extra combinators are provided.
<+> puts its arguments beside each other with a space between them,
sep (separate) is either like hsep or like vcat, depending on what fits
- cat is behaves like sep, but it uses <> for horizontal conposition
- fcat is behaves like fsep, but it uses <> for horizontal conposition
+ cat behaves like sep, but it uses <> for horizontal conposition
+ fcat behaves like fsep, but it uses <> for horizontal conposition
These new ones do the obvious things:
char, semi, comma, colon, space,
-}
module Text.PrettyPrint.HughesPJ (
+
+ -- * The document type
Doc, -- Abstract
- Mode(..), TextDetails(..),
- empty, isEmpty, nest,
+ -- * Primitive Documents
+ empty,
+ semi, comma, colon, space, equals,
+ lparen, rparen, lbrack, rbrack, lbrace, rbrace,
+ -- * Converting values into documents
text, char, ptext,
int, integer, float, double, rational,
+
+ -- * Wrapping documents in delimiters
parens, brackets, braces, quotes, doubleQuotes,
- semi, comma, colon, space, equals,
- lparen, rparen, lbrack, rbrack, lbrace, rbrace,
+ -- * Combining documents
(<>), (<+>), hcat, hsep,
($$), ($+$), vcat,
sep, cat,
fsep, fcat,
-
+ nest,
hang, punctuate,
--- renderStyle, -- Haskell 1.3 only
- render, fullRender
+ -- * Predicates on documents
+ isEmpty,
+
+ -- * Rendering documents
+
+ -- ** Default rendering
+ render,
+
+ -- ** Rendering with a particular style
+ Style(..),
+ style,
+ renderStyle,
+
+ -- ** General rendering
+ fullRender,
+ Mode(..), TextDetails(..),
+
) where
-- The primitive Doc values
-empty :: Doc
-isEmpty :: Doc -> Bool
-text :: String -> Doc
-char :: Char -> Doc
-
-semi, comma, colon, space, equals :: Doc
-lparen, rparen, lbrack, rbrack, lbrace, rbrace :: Doc
-
-parens, brackets, braces :: Doc -> Doc
-quotes, doubleQuotes :: Doc -> Doc
-
-int :: Int -> Doc
-integer :: Integer -> Doc
-float :: Float -> Doc
-double :: Double -> Doc
+isEmpty :: Doc -> Bool; -- ^ Returns 'True' if the document is empty
+
+empty :: Doc; -- ^ An empty document
+semi :: Doc; -- ^ A ';' character
+comma :: Doc; -- ^ A ',' character
+colon :: Doc; -- ^ A ':' character
+space :: Doc; -- ^ A space character
+equals :: Doc; -- ^ A '=' character
+lparen :: Doc; -- ^ A '(' character
+rparen :: Doc; -- ^ A ')' character
+lbrack :: Doc; -- ^ A '[' character
+rbrack :: Doc; -- ^ A ']' character
+lbrace :: Doc; -- ^ A '{' character
+rbrace :: Doc; -- ^ A '}' character
+
+text :: String -> Doc
+ptext :: String -> Doc
+char :: Char -> Doc
+int :: Int -> Doc
+integer :: Integer -> Doc
+float :: Float -> Doc
+double :: Double -> Doc
rational :: Rational -> Doc
+parens :: Doc -> Doc; -- ^ Wrap document in @(...)@
+brackets :: Doc -> Doc; -- ^ Wrap document in @[...]@
+braces :: Doc -> Doc; -- ^ Wrap document in @{...}@
+quotes :: Doc -> Doc; -- ^ Wrap document in @\'...\'@
+doubleQuotes :: Doc -> Doc; -- ^ Wrap document in @\"...\"@
+
-- Combining @Doc@ values
-(<>) :: Doc -> Doc -> Doc -- Beside
-hcat :: [Doc] -> Doc -- List version of <>
-(<+>) :: Doc -> Doc -> Doc -- Beside, separated by space
-hsep :: [Doc] -> Doc -- List version of <+>
+(<>) :: Doc -> Doc -> Doc; -- ^Beside
+hcat :: [Doc] -> Doc; -- ^List version of '<>'
+(<+>) :: Doc -> Doc -> Doc; -- ^Beside, separated by space
+hsep :: [Doc] -> Doc; -- ^List version of '<+>'
-($$) :: Doc -> Doc -> Doc -- Above; if there is no
- -- overlap it "dovetails" the two
-vcat :: [Doc] -> Doc -- List version of $$
+($$) :: Doc -> Doc -> Doc; -- ^Above; if there is no
+ -- overlap it \"dovetails\" the two
+($+$) :: Doc -> Doc -> Doc; -- ^Above, without dovetailing.
+vcat :: [Doc] -> Doc; -- ^List version of '$$'
-cat :: [Doc] -> Doc -- Either hcat or vcat
-sep :: [Doc] -> Doc -- Either hsep or vcat
-fcat :: [Doc] -> Doc -- ``Paragraph fill'' version of cat
-fsep :: [Doc] -> Doc -- ``Paragraph fill'' version of sep
+cat :: [Doc] -> Doc; -- ^ Either hcat or vcat
+sep :: [Doc] -> Doc; -- ^ Either hsep or vcat
+fcat :: [Doc] -> Doc; -- ^ \"Paragraph fill\" version of cat
+fsep :: [Doc] -> Doc; -- ^ \"Paragraph fill\" version of sep
-nest :: Int -> Doc -> Doc -- Nested
+nest :: Int -> Doc -> Doc; -- ^ Nested
-- GHC-specific ones.
-hang :: Doc -> Int -> Doc -> Doc
-punctuate :: Doc -> [Doc] -> [Doc] -- punctuate p [d1, ... dn] = [d1 <> p, d2 <> p, ... dn-1 <> p, dn]
+hang :: Doc -> Int -> Doc -> Doc; -- ^ @hang d1 n d2 = sep [d1, nest n d2]@
+punctuate :: Doc -> [Doc] -> [Doc]; -- ^ @punctuate p [d1, ... dn] = [d1 \<> p, d2 \<> p, ... dn-1 \<> p, dn]@
-- Displaying @Doc@ values.
instance Show Doc where
showsPrec prec doc cont = showDoc doc cont
-render :: Doc -> String -- Uses default style
-fullRender :: Mode
- -> Int -- Line length
- -> Float -- Ribbons per line
- -> (TextDetails -> a -> a) -- What to do with text
- -> a -- What to do at the end
- -> Doc
- -> a -- Result
+-- | Renders the document as a string using the default style
+render :: Doc -> String
+
+-- | The general rendering interface
+fullRender :: Mode -- ^Rendering mode
+ -> Int -- ^Line length
+ -> Float -- ^Ribbons per line
+ -> (TextDetails -> a -> a) -- ^What to do with text
+ -> a -- ^What to do at the end
+ -> Doc -- ^The document
+ -> a -- ^Result
-{- When we start using 1.3
+-- | Render the document as a string using a specified style
renderStyle :: Style -> Doc -> String
-data Style = Style { lineLength :: Int, -- In chars
- ribbonsPerLine :: Float, -- Ratio of ribbon length to line length
- mode :: Mode
- }
-style :: Style -- The default style
-style = Style { lineLength = 100, ribbonsPerLine = 2.5, mode = PageMode }
--}
-data Mode = PageMode -- Normal
- | ZigZagMode -- With zig-zag cuts
- | LeftMode -- No indentation, infinitely long lines
- | OneLineMode -- All on one line
+-- | A rendering style
+data Style
+ = Style { mode :: Mode -- ^ The rendering mode
+ , lineLength :: Int -- ^ Length of line, in chars
+ , ribbonsPerLine :: Float -- ^ Ratio of ribbon length to line length
+ }
+
+-- | The default style (@mode=PageMode, lineLength=100, ribbonsPerLine=1.5@)
+style :: Style
+style = Style { lineLength = 100, ribbonsPerLine = 1.5, mode = PageMode }
+-- | Rendering mode
+data Mode = PageMode -- ^Normal
+ | ZigZagMode -- ^With zig-zag cuts
+ | LeftMode -- ^No indentation, infinitely long lines
+ | OneLineMode -- ^All on one line
-- ---------------------------------------------------------------------------
-- The Doc calculus
-- A Doc represents a *set* of layouts. A Doc with
-- no occurrences of Union or NoDoc represents just one layout.
+-- | The abstract type of documents
data Doc
= Empty -- empty
| NilAbove Doc -- text "" $$ x
space_text = Chr ' '
nl_text = Chr '\n'
--- Here are the invariants:
-
--- * The argument of NilAbove is never Empty. Therefore
--- a NilAbove occupies at least two lines.
---
--- * The arugment of @TextBeside@ is never @Nest@.
---
---
--- * The layouts of the two arguments of @Union@ both flatten to the same
--- string.
---
--- * The arguments of @Union@ are either @TextBeside@, or @NilAbove@.
---
--- * The right argument of a union cannot be equivalent to the empty set
--- (@NoDoc@). If the left argument of a union is equivalent to the
--- empty set (@NoDoc@), then the @NoDoc@ appears in the first line.
-
--- * An empty document is always represented by @Empty@. It can't be
--- hidden inside a @Nest@, or a @Union@ of two @Empty@s.
-
--- * The first line of every layout in the left argument of @Union@ is
--- longer than the first line of any layout in the right argument.
--- (1) ensures that the left argument has a first line. In view of
--- (3), this invariant means that the right argument must have at
--- least two lines.
-
+{-
+ Here are the invariants:
+
+ * The argument of NilAbove is never Empty. Therefore
+ a NilAbove occupies at least two lines.
+
+ * The arugment of @TextBeside@ is never @Nest@.
+
+
+ * The layouts of the two arguments of @Union@ both flatten to the same
+ string.
+
+ * The arguments of @Union@ are either @TextBeside@, or @NilAbove@.
+
+ * The right argument of a union cannot be equivalent to the empty set
+ (@NoDoc@). If the left argument of a union is equivalent to the
+ empty set (@NoDoc@), then the @NoDoc@ appears in the first line.
+
+ * An empty document is always represented by @Empty@. It can't be
+ hidden inside a @Nest@, or a @Union@ of two @Empty@s.
+
+ * The first line of every layout in the left argument of @Union@ is
+ longer than the first line of any layout in the right argument.
+ (1) ensures that the left argument has a first line. In view of
+ (3), this invariant means that the right argument must have at
+ least two lines.
+-}
-- Arg of a NilAbove is always an RDoc
nilAbove_ p = NilAbove p
-- ---------------------------------------------------------------------------
-- Displaying the best layout
-{-
-renderStyle Style{mode, lineLength, ribbonsPerLine} doc
- = fullRender mode lineLength ribbonsPerLine doc ""
--}
+renderStyle style doc
+ = fullRender (mode style)
+ (lineLength style)
+ (ribbonsPerLine style)
+ string_txt
+ ""
+ doc
render doc = showDoc doc ""
showDoc doc rest = fullRender PageMode 100 1.5 string_txt rest doc
multi_ch 0 ch = ""
multi_ch n ch = ch : multi_ch (n - 1) ch
-spaces 0 = ""
-spaces n = ' ' : spaces (n - 1)
-
+-- (spaces n) generates a list of n spaces
+--
+-- It should never be called with 'n' < 0, but that can happen for reasons I don't understand
+-- Here's a test case:
+-- ncat x y = nest 4 $ cat [ x, y ]
+-- d1 = foldl1 ncat $ take 50 $ repeat $ char 'a'
+-- d2 = parens $ sep [ d1, text "+" , d1 ]
+-- main = print d2
+-- I don't feel motivated enough to find the Real Bug, so meanwhile we just test for n<=0
+spaces n | n <= 0 = ""
+ | otherwise = ' ' : spaces (n - 1)
+
+{- Comments from Johannes Waldmann about what the problem might be:
+
+ In the example above, d2 and d1 are deeply nested, but `text "+"' is not,
+ so the layout function tries to "out-dent" it.
+
+ when I look at the Doc values that are generated, there are lots of
+ Nest constructors with negative arguments. see this sample output of
+ d1 (obtained with hugs, :s -u)
+
+ tBeside (TextDetails_Chr 'a') 1 Doc_Empty) (Doc_NilAbove (Doc_Nest
+ (-241) (Doc_TextBeside (TextDetails_Chr 'a') 1 Doc_Empty)))))
+ (Doc_NilAbove (Doc_Nest (-236) (Doc_TextBeside (TextDetails_Chr 'a') 1
+ (Doc_NilAbove (Doc_Nest (-5) (Doc_TextBeside (TextDetails_Chr 'a') 1
+ Doc_Empty)))))))) (Doc_NilAbove (Doc_Nest (-231) (Doc_TextBeside
+ (TextDetails_Chr 'a') 1 (Doc_NilAbove (Doc_Nest (-5) (Doc_TextBeside
+ (TextDetails_Chr 'a') 1 (Doc_NilAbove (Doc_Nest (-5) (Doc_TextBeside
+ (TextDetails_Chr 'a') 1 Doc_Empty))))))))))) (Doc_NilAbove (Doc_Nest
+-}
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