----------------------------------------------------------------------------- -- | -- Module : Text.PrettyPrint.HughesPJ -- Copyright : (c) The University of Glasgow 2001 -- 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 -- -- Based on /The Design of a Pretty-printing Library/ -- in Advanced Functional Programming, -- Johan Jeuring and Erik Meijer (eds), LNCS 925 -- <http://www.cs.chalmers.se/~rjmh/Papers/pretty.ps> -- -- Heavily modified by Simon Peyton Jones, Dec 96 -- ----------------------------------------------------------------------------- {- Version 3.0 28 May 1997 * Cured massive performance bug. If you write foldl <> empty (map (text.show) [1..10000]) you get quadratic behaviour with V2.0. Why? For just the same reason as you get quadratic behaviour with left-associated (++) chains. This is really bad news. One thing a pretty-printer abstraction should certainly guarantee is insensivity to associativity. It matters: suddenly GHC's compilation times went up by a factor of 100 when I switched to the new pretty printer. I fixed it with a bit of a hack (because I wanted to get GHC back on the road). I added two new constructors to the Doc type, Above and Beside: <> = Beside $$ = Above Then, where I need to get to a "TextBeside" or "NilAbove" form I "force" the Doc to squeeze out these suspended calls to Beside and Above; but in so doing I re-associate. It's quite simple, but I'm not satisfied that I've done the best possible job. I'll send you the code if you are interested. * Added new exports: punctuate, hang int, integer, float, double, rational, lparen, rparen, lbrack, rbrack, lbrace, rbrace, * fullRender's type signature has changed. Rather than producing a string it now takes an extra couple of arguments that tells it how to glue fragments of output together: fullRender :: Mode -> Int -- Line length -> Float -- Ribbons per line -> (TextDetails -> a -> a) -- What to do with text -> a -- What to do at the end -> Doc -> a -- Result The "fragments" are encapsulated in the TextDetails data type: data TextDetails = Chr Char | Str String | PStr FAST_STRING The Chr and Str constructors are obvious enough. The PStr constructor has a packed string (FAST_STRING) inside it. It's generated by using the new "ptext" export. An advantage of this new setup is that you can get the renderer to do output directly (by passing in a function of type (TextDetails -> IO () -> IO ()), rather than producing a string that you then print. Version 2.0 24 April 1997 * Made empty into a left unit for <> as well as a right unit; it is also now true that nest k empty = empty which wasn't true before. * Fixed an obscure bug in sep that occassionally gave very weird behaviour * Added $+$ * Corrected and tidied up the laws and invariants ====================================================================== Relative to John's original paper, there are the following new features: 1. There's an empty document, "empty". It's a left and right unit for both <> and $$, and anywhere in the argument list for sep, hcat, hsep, vcat, fcat etc. 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 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, unless either argument is empty in which case it returns the other hcat is a list version of <> hsep is a list version of <+> vcat is a list version of $$ sep (separate) is either like hsep or like vcat, depending on what fits cat behaves like sep, but it uses <> for horizontal conposition fcat behaves like fsep, but it uses <> for horizontal conposition These new ones do the obvious things: char, semi, comma, colon, space, parens, brackets, braces, quotes, doubleQuotes 4. The "above" combinator, $$, now overlaps its two arguments if the last line of the top argument stops before the first line of the second begins. For example: text "hi" $$ nest 5 (text "there") lays out as hi there rather than hi there There are two places this is really useful a) When making labelled blocks, like this: Left -> code for left Right -> code for right LongLongLongLabel -> code for longlonglonglabel The block is on the same line as the label if the label is short, but on the next line otherwise. b) When laying out lists like this: [ first , second , third ] which some people like. But if the list fits on one line you want [first, second, third]. You can't do this with John's original combinators, but it's quite easy with the new $$. The combinator $+$ gives the original "never-overlap" behaviour. 5. Several different renderers are provided: * a standard one * one that uses cut-marks to avoid deeply-nested documents simply piling up in the right-hand margin * one that ignores indentation (fewer chars output; good for machines) * one that ignores indentation and newlines (ditto, only more so) 6. Numerous implementation tidy-ups Use of unboxed data types to speed up the implementation -} module Text.PrettyPrint.HughesPJ ( -- * The document type Doc, -- Abstract -- * Constructing documents -- ** Converting values into documents char, text, ptext, zeroWidthText, int, integer, float, double, rational, -- ** Simple derived documents semi, comma, colon, space, equals, lparen, rparen, lbrack, rbrack, lbrace, rbrace, -- ** Wrapping documents in delimiters parens, brackets, braces, quotes, doubleQuotes, -- ** Combining documents empty, (<>), (<+>), hcat, hsep, ($$), ($+$), vcat, sep, cat, fsep, fcat, nest, hang, punctuate, -- * Predicates on documents isEmpty, -- * Rendering documents -- ** Default rendering render, -- ** Rendering with a particular style Style(..), style, renderStyle, -- ** General rendering fullRender, Mode(..), TextDetails(..), ) where import Prelude infixl 6 <> infixl 6 <+> infixl 5 $$, $+$ -- --------------------------------------------------------------------------- -- The interface -- The primitive Doc values isEmpty :: Doc -> Bool; -- ^ Returns 'True' if the document is empty -- | The empty document, with no height and no width. -- 'empty' is the identity for '<>', '<+>', '$$' and '$+$', and anywhere -- in the argument list for 'sep', 'hcat', 'hsep', 'vcat', 'fcat' etc. empty :: Doc 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 -- | A document of height and width 1, containing a literal character. char :: Char -> Doc -- | A document of height 1 containing a literal string. -- 'text' satisfies the following laws: -- -- * @'text' s '<>' 'text' t = 'text' (s'++'t)@ -- -- * @'text' \"\" '<>' x = x@, if @x@ non-empty -- -- The side condition on the last law is necessary because @'text' \"\"@ -- has height 1, while 'empty' has no height. text :: String -> Doc -- | An obsolete function, now identical to 'text'. ptext :: String -> Doc -- | Some text, but without any width. Use for non-printing text -- such as a HTML or Latex tags zeroWidthText :: String -> Doc int :: Int -> Doc; -- ^ @int n = text (show n)@ integer :: Integer -> Doc; -- ^ @integer n = text (show n)@ float :: Float -> Doc; -- ^ @float n = text (show n)@ double :: Double -> Doc; -- ^ @double n = text (show n)@ rational :: Rational -> Doc; -- ^ @rational n = text (show n)@ 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 -- | Beside. -- '<>' is associative, with identity 'empty'. (<>) :: Doc -> Doc -> Doc -- | Beside, separated by space, unless one of the arguments is 'empty'. -- '<+>' is associative, with identity 'empty'. (<+>) :: Doc -> Doc -> Doc -- | 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 '$$' (y '<>' z)@, if @y@ non-empty. -- ($$) :: Doc -> Doc -> Doc -- | Above, with no overlapping. -- '$+$' is associative, with identity 'empty'. ($+$) :: Doc -> Doc -> Doc hcat :: [Doc] -> Doc; -- ^List version of '<>'. hsep :: [Doc] -> Doc; -- ^List version of '<+>'. vcat :: [Doc] -> Doc; -- ^List version of '$$'. cat :: [Doc] -> Doc; -- ^ Either 'hcat' or 'vcat'. sep :: [Doc] -> Doc; -- ^ Either 'hsep' or 'vcat'. fcat :: [Doc] -> Doc; -- ^ \"Paragraph fill\" version of 'cat'. fsep :: [Doc] -> Doc; -- ^ \"Paragraph fill\" version of 'sep'. -- | Nest (or indent) a document by a given number of positions -- (which may also be negative). 'nest' satisfies the laws: -- -- * @'nest' 0 x = x@ -- -- * @'nest' k ('nest' k' x) = 'nest' (k+k') x@ -- -- * @'nest' k (x '<>' y) = 'nest' k z '<>' 'nest' k y@ -- -- * @'nest' k (x '$$' y) = 'nest' k x '$$' 'nest' k y@ -- -- * @'nest' k 'empty' = 'empty'@ -- -- * @x '<>' 'nest' k y = x '<>' y@, if @x@ non-empty -- -- The side condition on the last law is needed because -- 'empty' is a left identity for '<>'. nest :: Int -> Doc -> Doc -- GHC-specific ones. -- | @hang d1 n d2 = sep [d1, nest n d2]@ hang :: Doc -> Int -> Doc -> Doc -- | @punctuate p [d1, ... dn] = [d1 \<> p, d2 \<> p, ... dn-1 \<> p, dn]@ punctuate :: Doc -> [Doc] -> [Doc] -- Displaying @Doc@ values. instance Show Doc where showsPrec _ doc cont = showDoc doc cont -- | Renders the document as a string using the default 'style'. render :: Doc -> String -- | The general rendering interface. fullRender :: Mode -- ^Rendering mode -> Int -- ^Line length -> Float -- ^Ribbons per line -> (TextDetails -> a -> a) -- ^What to do with text -> a -- ^What to do at the end -> Doc -- ^The document -> a -- ^Result -- | Render the document as a string using a specified style. renderStyle :: Style -> Doc -> String -- | A rendering style. data Style = Style { mode :: Mode -- ^ The rendering mode , lineLength :: Int -- ^ Length of line, in chars , ribbonsPerLine :: Float -- ^ Ratio of ribbon length to line length } -- | The default style (@mode=PageMode, lineLength=100, ribbonsPerLine=1.5@). style :: Style style = Style { lineLength = 100, ribbonsPerLine = 1.5, mode = PageMode } -- | Rendering mode. data Mode = PageMode -- ^Normal | ZigZagMode -- ^With zig-zag cuts | LeftMode -- ^No indentation, infinitely long lines | OneLineMode -- ^All on one line -- --------------------------------------------------------------------------- -- The Doc calculus -- The Doc combinators satisfy the following laws: {- Laws for $$ ~~~~~~~~~~~ <a1> (x $$ y) $$ z = x $$ (y $$ z) <a2> empty $$ x = x <a3> x $$ empty = x ...ditto $+$... Laws for <> ~~~~~~~~~~~ <b1> (x <> y) <> z = x <> (y <> z) <b2> empty <> x = empty <b3> x <> empty = x ...ditto <+>... Laws for text ~~~~~~~~~~~~~ <t1> text s <> text t = text (s++t) <t2> text "" <> x = x, if x non-empty ** because of law n6, t2 only holds if x doesn't ** start with `nest'. Laws for nest ~~~~~~~~~~~~~ <n1> nest 0 x = x <n2> nest k (nest k' x) = nest (k+k') x <n3> nest k (x <> y) = nest k z <> nest k y <n4> nest k (x $$ y) = nest k x $$ nest k y <n5> nest k empty = empty <n6> x <> nest k y = x <> y, if x non-empty ** Note the side condition on <n6>! It is this that ** makes it OK for empty to be a left unit for <>. Miscellaneous ~~~~~~~~~~~~~ <m1> (text s <> x) $$ y = text s <> ((text "" <> x) $$ nest (-length s) y) <m2> (x $$ y) <> z = x $$ (y <> z) if y non-empty Laws for list versions ~~~~~~~~~~~~~~~~~~~~~~ <l1> sep (ps++[empty]++qs) = sep (ps ++ qs) ...ditto hsep, hcat, vcat, fill... <l2> nest k (sep ps) = sep (map (nest k) ps) ...ditto hsep, hcat, vcat, fill... Laws for oneLiner ~~~~~~~~~~~~~~~~~ <o1> oneLiner (nest k p) = nest k (oneLiner p) <o2> oneLiner (x <> y) = oneLiner x <> oneLiner y You might think that the following verion of <m1> would be neater: <3 NO> (text s <> x) $$ y = text s <> ((empty <> x)) $$ nest (-length s) y) But it doesn't work, for if x=empty, we would have text s $$ y = text s <> (empty $$ nest (-length s) y) = text s <> nest (-length s) y -} -- --------------------------------------------------------------------------- -- Simple derived definitions semi = char ';' colon = char ':' comma = char ',' space = char ' ' equals = char '=' lparen = char '(' rparen = char ')' lbrack = char '[' rbrack = char ']' lbrace = char '{' rbrace = char '}' int n = text (show n) integer n = text (show n) float n = text (show n) double n = text (show n) rational n = text (show n) -- SIGBJORN wrote instead: -- rational n = text (show (fromRationalX n)) quotes p = char '\'' <> p <> char '\'' doubleQuotes p = char '"' <> p <> char '"' parens p = char '(' <> p <> char ')' brackets p = char '[' <> p <> char ']' braces p = char '{' <> p <> char '}' -- lazy list versions hcat = reduceAB . foldr (beside_' False) empty hsep = reduceAB . foldr (beside_' True) empty vcat = reduceAB . foldr (above_' True) empty beside_' :: Bool -> Doc -> Doc -> Doc beside_' _ p Empty = p beside_' g p q = Beside p g q above_' :: Bool -> Doc -> Doc -> Doc above_' _ p Empty = p above_' g p q = Above p g q reduceAB :: Doc -> Doc reduceAB (Above Empty _ q) = q reduceAB (Beside Empty _ q) = q reduceAB doc = doc hang d1 n d2 = sep [d1, nest n d2] punctuate _ [] = [] punctuate p (d:ds) = go d ds where go d' [] = [d'] go d' (e:es) = (d' <> p) : go e es -- --------------------------------------------------------------------------- -- The Doc data type -- 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. -- The 'Show' instance is equivalent to using 'render'. data Doc = Empty -- empty | NilAbove Doc -- text "" $$ x | TextBeside TextDetails !Int Doc -- text s <> x | Nest !Int Doc -- nest k x | Union Doc Doc -- ul `union` ur | NoDoc -- The empty set of documents | Beside Doc Bool Doc -- True <=> space between | Above Doc Bool Doc -- True <=> never overlap type RDoc = Doc -- RDoc is a "reduced Doc", guaranteed not to have a top-level Above or Beside reduceDoc :: Doc -> RDoc reduceDoc (Beside p g q) = beside p g (reduceDoc q) reduceDoc (Above p g q) = above p g (reduceDoc q) reduceDoc p = p data TextDetails = Chr Char | Str String | PStr String space_text, nl_text :: TextDetails space_text = Chr ' ' nl_text = Chr '\n' {- Here are the invariants: 1) The argument of NilAbove is never Empty. Therefore a NilAbove occupies at least two lines. 2) The argument of @TextBeside@ is never @Nest@. 3) The layouts of the two arguments of @Union@ both flatten to the same string. 4) The arguments of @Union@ are either @TextBeside@, or @NilAbove@. 5) A @NoDoc@ may only appear on the first line of the left argument of an union. Therefore, the right argument of an union can never be equivalent to the empty set (@NoDoc@). 6) An empty document is always represented by @Empty@. It can't be hidden inside a @Nest@, or a @Union@ of two @Empty@s. 7) 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. -} -- Invariant: Args to the 4 functions below are always RDocs nilAbove_ :: RDoc -> RDoc nilAbove_ p = NilAbove p -- Arg of a TextBeside is always an RDoc textBeside_ :: TextDetails -> Int -> RDoc -> RDoc textBeside_ s sl p = TextBeside s sl p nest_ :: Int -> RDoc -> RDoc nest_ k p = Nest k p union_ :: RDoc -> RDoc -> RDoc union_ p q = Union p q -- Notice the difference between -- * NoDoc (no documents) -- * Empty (one empty document; no height and no width) -- * text "" (a document containing the empty string; -- one line high, but has no width) -- --------------------------------------------------------------------------- -- @empty@, @text@, @nest@, @union@ empty = Empty isEmpty Empty = True isEmpty _ = False char c = textBeside_ (Chr c) 1 Empty text s = case length s of {sl -> textBeside_ (Str s) sl Empty} ptext s = case length s of {sl -> textBeside_ (PStr s) sl Empty} zeroWidthText s = textBeside_ (Str s) 0 Empty nest k p = mkNest k (reduceDoc p) -- Externally callable version -- mkNest checks for Nest's invariant that it doesn't have an Empty inside it mkNest :: Int -> Doc -> Doc mkNest k _ | k `seq` False = undefined mkNest k (Nest k1 p) = mkNest (k + k1) p mkNest _ NoDoc = NoDoc mkNest _ Empty = Empty mkNest 0 p = p -- Worth a try! mkNest k p = nest_ k p -- mkUnion checks for an empty document mkUnion :: Doc -> Doc -> Doc mkUnion Empty _ = Empty mkUnion p q = p `union_` q -- --------------------------------------------------------------------------- -- Vertical composition @$$@ above_ :: Doc -> Bool -> Doc -> Doc above_ p _ Empty = p above_ Empty _ q = q above_ p g q = Above p g q p $$ q = above_ p False q p $+$ q = above_ p True q above :: Doc -> Bool -> RDoc -> RDoc above (Above p g1 q1) g2 q2 = above p g1 (above q1 g2 q2) above p@(Beside _ _ _) g q = aboveNest (reduceDoc p) g 0 (reduceDoc q) above p g q = aboveNest p g 0 (reduceDoc q) aboveNest :: RDoc -> Bool -> Int -> RDoc -> RDoc -- Specfication: aboveNest p g k q = p $g$ (nest k q) aboveNest _ _ k _ | k `seq` False = undefined aboveNest NoDoc _ _ _ = NoDoc aboveNest (p1 `Union` p2) g k q = aboveNest p1 g k q `union_` aboveNest p2 g k q aboveNest Empty _ k q = mkNest k q aboveNest (Nest k1 p) g k q = nest_ k1 (aboveNest p g (k - k1) q) -- p can't be Empty, so no need for mkNest aboveNest (NilAbove p) g k q = nilAbove_ (aboveNest p g k q) aboveNest (TextBeside s sl p) g k q = k1 `seq` textBeside_ s sl rest where k1 = k - sl rest = case p of Empty -> nilAboveNest g k1 q _ -> aboveNest p g k1 q aboveNest (Above {}) _ _ _ = error "aboveNest Above" aboveNest (Beside {}) _ _ _ = error "aboveNest Beside" nilAboveNest :: Bool -> Int -> RDoc -> RDoc -- Specification: text s <> nilaboveNest g k q -- = text s <> (text "" $g$ nest k q) nilAboveNest _ k _ | k `seq` False = undefined nilAboveNest _ _ Empty = Empty -- Here's why the "text s <>" is in the spec! nilAboveNest g k (Nest k1 q) = nilAboveNest g (k + k1) q nilAboveNest g k q | (not g) && (k > 0) -- No newline if no overlap = textBeside_ (Str (spaces k)) k q | otherwise -- Put them really above = nilAbove_ (mkNest k q) -- --------------------------------------------------------------------------- -- Horizontal composition @<>@ beside_ :: Doc -> Bool -> Doc -> Doc beside_ p _ Empty = p beside_ Empty _ q = q beside_ p g q = Beside p g q p <> q = beside_ p False q p <+> q = beside_ p True q beside :: Doc -> Bool -> RDoc -> RDoc -- Specification: beside g p q = p <g> q beside NoDoc _ _ = NoDoc beside (p1 `Union` p2) g q = (beside p1 g q) `union_` (beside p2 g q) beside Empty _ q = q beside (Nest k p) g q = nest_ k (beside p g q) -- p non-empty beside p@(Beside p1 g1 q1) g2 q2 {- (A `op1` B) `op2` C == A `op1` (B `op2` C) iff op1 == op2 [ && (op1 == <> || op1 == <+>) ] -} | g1 == g2 = beside p1 g1 (beside q1 g2 q2) | otherwise = beside (reduceDoc p) g2 q2 beside p@(Above _ _ _) g q = beside (reduceDoc p) g q beside (NilAbove p) g q = nilAbove_ (beside p g q) beside (TextBeside s sl p) g q = textBeside_ s sl rest where rest = case p of Empty -> nilBeside g q _ -> beside p g q nilBeside :: Bool -> RDoc -> RDoc -- Specification: text "" <> nilBeside g p -- = text "" <g> p nilBeside _ Empty = Empty -- Hence the text "" in the spec nilBeside g (Nest _ p) = nilBeside g p nilBeside g p | g = textBeside_ space_text 1 p | otherwise = p -- --------------------------------------------------------------------------- -- Separate, @sep@, Hughes version -- Specification: sep ps = oneLiner (hsep ps) -- `union` -- vcat ps sep = sepX True -- Separate with spaces cat = sepX False -- Don't sepX :: Bool -> [Doc] -> Doc sepX _ [] = empty sepX x (p:ps) = sep1 x (reduceDoc p) 0 ps -- Specification: sep1 g k ys = sep (x : map (nest k) ys) -- = oneLiner (x <g> nest k (hsep ys)) -- `union` x $$ nest k (vcat ys) sep1 :: Bool -> RDoc -> Int -> [Doc] -> RDoc sep1 _ _ k _ | k `seq` False = undefined sep1 _ NoDoc _ _ = NoDoc sep1 g (p `Union` q) k ys = sep1 g p k ys `union_` (aboveNest q False k (reduceDoc (vcat ys))) sep1 g Empty k ys = mkNest k (sepX g ys) sep1 g (Nest n p) k ys = nest_ n (sep1 g p (k - n) ys) sep1 _ (NilAbove p) k ys = nilAbove_ (aboveNest p False k (reduceDoc (vcat ys))) sep1 g (TextBeside s sl p) k ys = textBeside_ s sl (sepNB g p (k - sl) ys) sep1 _ (Above {}) _ _ = error "sep1 Above" sep1 _ (Beside {}) _ _ = error "sep1 Beside" -- Specification: sepNB p k ys = sep1 (text "" <> p) k ys -- Called when we have already found some text in the first item -- We have to eat up nests sepNB :: Bool -> Doc -> Int -> [Doc] -> Doc sepNB g (Nest _ p) k ys = sepNB g p k ys -- Never triggered, because of invariant (2) sepNB g Empty k ys = oneLiner (nilBeside g (reduceDoc rest)) `mkUnion` nilAboveNest True k (reduceDoc (vcat ys)) where rest | g = hsep ys | otherwise = hcat ys sepNB g p k ys = sep1 g p k ys -- --------------------------------------------------------------------------- -- @fill@ fsep = fill True fcat = fill False -- Specification: -- -- fill g docs = fillIndent 0 docs -- -- fillIndent k [] = [] -- fillIndent k [p] = p -- fillIndent k (p1:p2:ps) = -- oneLiner p1 <g> fillIndent (k + length p1 + g ? 1 : 0) (remove_nests (oneLiner p2) : ps) -- `Union` -- (p1 $*$ nest (-k) (fillIndent 0 ps)) -- -- $*$ is defined for layouts (not Docs) as -- layout1 $*$ layout2 | hasMoreThanOneLine layout1 = layout1 $$ layout2 -- | otherwise = layout1 $+$ layout2 fill :: Bool -> [Doc] -> RDoc fill _ [] = empty fill g (p:ps) = fill1 g (reduceDoc p) 0 ps fill1 :: Bool -> RDoc -> Int -> [Doc] -> Doc fill1 _ _ k _ | k `seq` False = undefined fill1 _ NoDoc _ _ = NoDoc fill1 g (p `Union` q) k ys = fill1 g p k ys `union_` (aboveNest q False k (fill g ys)) fill1 g Empty k ys = mkNest k (fill g ys) fill1 g (Nest n p) k ys = nest_ n (fill1 g p (k - n) ys) fill1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (fill g ys)) fill1 g (TextBeside s sl p) k ys = textBeside_ s sl (fillNB g p (k - sl) ys) fill1 _ (Above {}) _ _ = error "fill1 Above" fill1 _ (Beside {}) _ _ = error "fill1 Beside" fillNB :: Bool -> Doc -> Int -> [Doc] -> Doc fillNB _ _ k _ | k `seq` False = undefined fillNB g (Nest _ p) k ys = fillNB g p k ys -- Never triggered, because of invariant (2) fillNB _ Empty _ [] = Empty fillNB g Empty k (Empty:ys) = fillNB g Empty k ys fillNB g Empty k (y:ys) = fillNBE g k y ys fillNB g p k ys = fill1 g p k ys fillNBE :: Bool -> Int -> Doc -> [Doc] -> Doc fillNBE g k y ys = nilBeside g (fill1 g ((elideNest . oneLiner . reduceDoc) y) k1 ys) `mkUnion` nilAboveNest True k (fill g (y:ys)) where k1 | g = k - 1 | otherwise = k elideNest :: Doc -> Doc elideNest (Nest _ d) = d elideNest d = d -- --------------------------------------------------------------------------- -- Selecting the best layout best :: Mode -> Int -- Line length -> Int -- Ribbon length -> RDoc -> RDoc -- No unions in here! best OneLineMode _ _ p0 = get p0 -- unused, due to the use of easy_display in full_render where get Empty = Empty get NoDoc = NoDoc get (NilAbove p) = nilAbove_ (get p) get (TextBeside s sl p) = textBeside_ s sl (get p) get (Nest _ p) = get p -- Elide nest get (p `Union` q) = first (get p) (get q) get (Above {}) = error "best OneLineMode get Above" get (Beside {}) = error "best OneLineMode get Beside" best _ w0 r p0 = get w0 p0 where get :: Int -- (Remaining) width of line -> Doc -> Doc get w _ | w==0 && False = undefined get _ Empty = Empty get _ NoDoc = NoDoc get w (NilAbove p) = nilAbove_ (get w p) get w (TextBeside s sl p) = textBeside_ s sl (get1 w sl p) get w (Nest k p) = nest_ k (get (w - k) p) get w (p `Union` q) = nicest w r (get w p) (get w q) get _ (Above {}) = error "best get Above" get _ (Beside {}) = error "best get Beside" get1 :: Int -- (Remaining) width of line -> Int -- Amount of first line already eaten up -> Doc -- This is an argument to TextBeside => eat Nests -> Doc -- No unions in here! get1 w _ _ | w==0 && False = undefined get1 _ _ Empty = Empty get1 _ _ NoDoc = NoDoc get1 w sl (NilAbove p) = nilAbove_ (get (w - sl) p) get1 w sl (TextBeside t tl p) = textBeside_ t tl (get1 w (sl + tl) p) get1 w sl (Nest _ p) = get1 w sl p get1 w sl (p `Union` q) = nicest1 w r sl (get1 w sl p) (get1 w sl q) get1 _ _ (Above {}) = error "best get1 Above" get1 _ _ (Beside {}) = error "best get1 Beside" nicest :: Int -> Int -> Doc -> Doc -> Doc nicest w r p q = nicest1 w r 0 p q nicest1 :: Int -> Int -> Int -> Doc -> Doc -> Doc nicest1 w r sl p q | fits ((w `minn` r) - sl) p = p | otherwise = q fits :: Int -- Space available -> Doc -> Bool -- True if *first line* of Doc fits in space available fits n _ | n < 0 = False fits _ NoDoc = False fits _ Empty = True fits _ (NilAbove _) = True fits n (TextBeside _ sl p) = fits (n - sl) p fits _ (Above {}) = error "fits Above" fits _ (Beside {}) = error "fits Beside" fits _ (Union {}) = error "fits Union" fits _ (Nest {}) = error "fits Nest" minn :: Int -> Int -> Int minn x y | x < y = x | otherwise = y -- @first@ and @nonEmptySet@ are similar to @nicest@ and @fits@, only simpler. -- @first@ returns its first argument if it is non-empty, otherwise its second. first :: Doc -> Doc -> Doc first p q | nonEmptySet p = p -- unused, because (get OneLineMode) is unused | otherwise = q nonEmptySet :: Doc -> Bool nonEmptySet NoDoc = False nonEmptySet (_ `Union` _) = True nonEmptySet Empty = True nonEmptySet (NilAbove _) = True -- NoDoc always in first line nonEmptySet (TextBeside _ _ p) = nonEmptySet p nonEmptySet (Nest _ p) = nonEmptySet p nonEmptySet (Above {}) = error "nonEmptySet Above" nonEmptySet (Beside {}) = error "nonEmptySet Beside" -- @oneLiner@ returns the one-line members of the given set of @Doc@s. oneLiner :: Doc -> Doc oneLiner NoDoc = NoDoc oneLiner Empty = Empty oneLiner (NilAbove _) = NoDoc oneLiner (TextBeside s sl p) = textBeside_ s sl (oneLiner p) oneLiner (Nest k p) = nest_ k (oneLiner p) oneLiner (p `Union` _) = oneLiner p oneLiner (Above {}) = error "oneLiner Above" oneLiner (Beside {}) = error "oneLiner Beside" -- --------------------------------------------------------------------------- -- Displaying the best layout renderStyle the_style doc = fullRender (mode the_style) (lineLength the_style) (ribbonsPerLine the_style) string_txt "" doc render doc = showDoc doc "" showDoc :: Doc -> String -> String showDoc doc rest = fullRender PageMode 100 1.5 string_txt rest doc string_txt :: TextDetails -> String -> String string_txt (Chr c) s = c:s string_txt (Str s1) s2 = s1 ++ s2 string_txt (PStr s1) s2 = s1 ++ s2 fullRender OneLineMode _ _ txt end doc = easy_display space_text txt end (reduceDoc doc) fullRender LeftMode _ _ txt end doc = easy_display nl_text txt end (reduceDoc doc) fullRender the_mode line_length ribbons_per_line txt end doc = display the_mode line_length ribbon_length txt end best_doc where best_doc = best the_mode hacked_line_length ribbon_length (reduceDoc doc) hacked_line_length, ribbon_length :: Int ribbon_length = round (fromIntegral line_length / ribbons_per_line) hacked_line_length = case the_mode of ZigZagMode -> maxBound _ -> line_length display :: Mode -> Int -> Int -> (TextDetails -> a -> a) -> a -> Doc -> a display the_mode page_width ribbon_width txt end doc = case page_width - ribbon_width of { gap_width -> case gap_width `quot` 2 of { shift -> let lay k _ | k `seq` False = undefined lay k (Nest k1 p) = lay (k + k1) p lay _ Empty = end lay _ (Above {}) = error "display lay Above" lay _ (Beside {}) = error "display lay Beside" lay _ NoDoc = error "display lay NoDoc" lay _ (Union {}) = error "display lay Union" lay k (NilAbove p) = nl_text `txt` lay k p lay k (TextBeside s sl p) = case the_mode of ZigZagMode | k >= gap_width -> nl_text `txt` ( Str (multi_ch shift '/') `txt` ( nl_text `txt` ( lay1 (k - shift) s sl p))) | k < 0 -> nl_text `txt` ( Str (multi_ch shift '\\') `txt` ( nl_text `txt` ( lay1 (k + shift) s sl p ))) _ -> lay1 k s sl p lay1 k _ sl _ | k+sl `seq` False = undefined lay1 k s sl p = Str (indent k) `txt` (s `txt` lay2 (k + sl) p) lay2 k _ | k `seq` False = undefined lay2 k (NilAbove p) = nl_text `txt` lay k p lay2 k (TextBeside s sl p) = s `txt` (lay2 (k + sl) p) lay2 k (Nest _ p) = lay2 k p lay2 _ Empty = end lay2 _ (Above {}) = error "display lay2 Above" lay2 _ (Beside {}) = error "display lay2 Beside" lay2 _ NoDoc = error "display lay2 NoDoc" lay2 _ (Union {}) = error "display lay2 Union" in lay 0 doc }} cant_fail :: a cant_fail = error "easy_display: NoDoc" easy_display :: TextDetails -> (TextDetails -> a -> a) -> a -> Doc -> a easy_display nl_space_text txt end doc = lay doc cant_fail where lay NoDoc no_doc = no_doc lay (Union _p q) _ = {- lay p -} (lay q cant_fail) -- Second arg can't be NoDoc lay (Nest _ p) no_doc = lay p no_doc lay Empty _ = end lay (NilAbove p) _ = nl_space_text `txt` lay p cant_fail -- NoDoc always on first line lay (TextBeside s _ p) no_doc = s `txt` lay p no_doc lay (Above {}) _ = error "easy_display Above" lay (Beside {}) _ = error "easy_display Beside" -- OLD version: we shouldn't rely on tabs being 8 columns apart in the output. -- indent n | n >= 8 = '\t' : indent (n - 8) -- | otherwise = spaces n indent :: Int -> String indent n = spaces n multi_ch :: Int -> Char -> String multi_ch 0 _ = "" multi_ch n ch = ch : multi_ch (n - 1) ch -- (spaces n) generates a list of n spaces -- -- returns the empty string on negative argument. -- spaces :: Int -> String spaces n {- | n < 0 = trace "Warning: negative indentation" "" -} | n <= 0 = "" | otherwise = ' ' : spaces (n - 1) {- Q: What is the reason for negative indentation (i.e. argument to indent is < 0) ? A: This indicates an error in the library client's code. If we compose a <> b, and the first line of b is more indented than some other lines of b, the law <n6> (<> eats nests) may cause the pretty printer to produce an invalid layout: doc |0123345 ------------------ d1 |a...| d2 |...b| |c...| d1<>d2 |ab..| c|....| Consider a <> b, let `s' be the length of the last line of `a', `k' the indentation of the first line of b, and `k0' the indentation of the left-most line b_i of b. The produced layout will have negative indentation if `k - k0 > s', as the first line of b will be put on the (s+1)th column, effectively translating b horizontally by (k-s). Now if the i^th line of b has an indentation k0 < (k-s), it is translated out-of-page, causing `negative indentation'. -}