1 -----------------------------------------------------------------------------
3 -- Module : Text.PrettyPrint.HughesPJ
4 -- Copyright : (c) The University of Glasgow 2001
5 -- License : BSD-style (see the file libraries/base/LICENSE)
7 -- Maintainer : libraries@haskell.org
8 -- Stability : provisional
9 -- Portability : portable
11 -- John Hughes's and Simon Peyton Jones's Pretty Printer Combinators
13 -- Based on /The Design of a Pretty-printing Library/
14 -- in Advanced Functional Programming,
15 -- Johan Jeuring and Erik Meijer (eds), LNCS 925
16 -- <http://www.cs.chalmers.se/~rjmh/Papers/pretty.ps>
18 -- Heavily modified by Simon Peyton Jones, Dec 96
20 -----------------------------------------------------------------------------
23 Version 3.0 28 May 1997
24 * Cured massive performance bug. If you write
26 foldl <> empty (map (text.show) [1..10000])
28 you get quadratic behaviour with V2.0. Why? For just the same
29 reason as you get quadratic behaviour with left-associated (++)
32 This is really bad news. One thing a pretty-printer abstraction
33 should certainly guarantee is insensivity to associativity. It
34 matters: suddenly GHC's compilation times went up by a factor of
35 100 when I switched to the new pretty printer.
37 I fixed it with a bit of a hack (because I wanted to get GHC back
38 on the road). I added two new constructors to the Doc type, Above
44 Then, where I need to get to a "TextBeside" or "NilAbove" form I
45 "force" the Doc to squeeze out these suspended calls to Beside and
46 Above; but in so doing I re-associate. It's quite simple, but I'm
47 not satisfied that I've done the best possible job. I'll send you
48 the code if you are interested.
52 int, integer, float, double, rational,
53 lparen, rparen, lbrack, rbrack, lbrace, rbrace,
55 * fullRender's type signature has changed. Rather than producing a
56 string it now takes an extra couple of arguments that tells it how
57 to glue fragments of output together:
61 -> Float -- Ribbons per line
62 -> (TextDetails -> a -> a) -- What to do with text
63 -> a -- What to do at the end
67 The "fragments" are encapsulated in the TextDetails data type:
69 data TextDetails = Chr Char
73 The Chr and Str constructors are obvious enough. The PStr
74 constructor has a packed string (FAST_STRING) inside it. It's
75 generated by using the new "ptext" export.
77 An advantage of this new setup is that you can get the renderer to
78 do output directly (by passing in a function of type (TextDetails
79 -> IO () -> IO ()), rather than producing a string that you then
83 Version 2.0 24 April 1997
84 * Made empty into a left unit for <> as well as a right unit;
85 it is also now true that
87 which wasn't true before.
89 * Fixed an obscure bug in sep that occassionally gave very weird behaviour
93 * Corrected and tidied up the laws and invariants
95 ======================================================================
96 Relative to John's original paper, there are the following new features:
98 1. There's an empty document, "empty". It's a left and right unit for
99 both <> and $$, and anywhere in the argument list for
100 sep, hcat, hsep, vcat, fcat etc.
102 It is Really Useful in practice.
104 2. There is a paragraph-fill combinator, fsep, that's much like sep,
105 only it keeps fitting things on one line until it can't fit any more.
107 3. Some random useful extra combinators are provided.
108 <+> puts its arguments beside each other with a space between them,
109 unless either argument is empty in which case it returns the other
112 hcat is a list version of <>
113 hsep is a list version of <+>
114 vcat is a list version of $$
116 sep (separate) is either like hsep or like vcat, depending on what fits
118 cat behaves like sep, but it uses <> for horizontal conposition
119 fcat behaves like fsep, but it uses <> for horizontal conposition
121 These new ones do the obvious things:
122 char, semi, comma, colon, space,
123 parens, brackets, braces,
126 4. The "above" combinator, $$, now overlaps its two arguments if the
127 last line of the top argument stops before the first line of the
130 For example: text "hi" $$ nest 5 "there"
137 There are two places this is really useful
139 a) When making labelled blocks, like this:
140 Left -> code for left
141 Right -> code for right
143 code for longlonglonglabel
144 The block is on the same line as the label if the label is
145 short, but on the next line otherwise.
147 b) When laying out lists like this:
152 which some people like. But if the list fits on one line
153 you want [first, second, third]. You can't do this with
154 John's original combinators, but it's quite easy with the
157 The combinator $+$ gives the original "never-overlap" behaviour.
159 5. Several different renderers are provided:
161 * one that uses cut-marks to avoid deeply-nested documents
162 simply piling up in the right-hand margin
163 * one that ignores indentation (fewer chars output; good for machines)
164 * one that ignores indentation and newlines (ditto, only more so)
166 6. Numerous implementation tidy-ups
167 Use of unboxed data types to speed up the implementation
170 module Text.PrettyPrint.HughesPJ (
172 -- * The document type
175 -- * Primitive Documents
177 semi, comma, colon, space, equals,
178 lparen, rparen, lbrack, rbrack, lbrace, rbrace,
180 -- * Converting values into documents
182 int, integer, float, double, rational,
184 -- * Wrapping documents in delimiters
185 parens, brackets, braces, quotes, doubleQuotes,
187 -- * Combining documents
188 (<>), (<+>), hcat, hsep,
195 -- * Predicates on documents
198 -- * Rendering documents
200 -- ** Default rendering
203 -- ** Rendering with a particular style
208 -- ** General rendering
210 Mode(..), TextDetails(..),
221 -- ---------------------------------------------------------------------------
224 -- The primitive Doc values
226 isEmpty :: Doc -> Bool; -- ^ Returns 'True' if the document is empty
228 empty :: Doc; -- ^ An empty document
229 semi :: Doc; -- ^ A ';' character
230 comma :: Doc; -- ^ A ',' character
231 colon :: Doc; -- ^ A ':' character
232 space :: Doc; -- ^ A space character
233 equals :: Doc; -- ^ A '=' character
234 lparen :: Doc; -- ^ A '(' character
235 rparen :: Doc; -- ^ A ')' character
236 lbrack :: Doc; -- ^ A '[' character
237 rbrack :: Doc; -- ^ A ']' character
238 lbrace :: Doc; -- ^ A '{' character
239 rbrace :: Doc; -- ^ A '}' character
241 text :: String -> Doc
242 ptext :: String -> Doc
245 integer :: Integer -> Doc
246 float :: Float -> Doc
247 double :: Double -> Doc
248 rational :: Rational -> Doc
251 parens :: Doc -> Doc; -- ^ Wrap document in @(...)@
252 brackets :: Doc -> Doc; -- ^ Wrap document in @[...]@
253 braces :: Doc -> Doc; -- ^ Wrap document in @{...}@
254 quotes :: Doc -> Doc; -- ^ Wrap document in @\'...\'@
255 doubleQuotes :: Doc -> Doc; -- ^ Wrap document in @\"...\"@
257 -- Combining @Doc@ values
259 (<>) :: Doc -> Doc -> Doc; -- ^Beside
260 hcat :: [Doc] -> Doc; -- ^List version of '<>'
261 (<+>) :: Doc -> Doc -> Doc; -- ^Beside, separated by space
262 hsep :: [Doc] -> Doc; -- ^List version of '<+>'
264 ($$) :: Doc -> Doc -> Doc; -- ^Above; if there is no
265 -- overlap it \"dovetails\" the two
266 ($+$) :: Doc -> Doc -> Doc; -- ^Above, without dovetailing.
267 vcat :: [Doc] -> Doc; -- ^List version of '$$'
269 cat :: [Doc] -> Doc; -- ^ Either hcat or vcat
270 sep :: [Doc] -> Doc; -- ^ Either hsep or vcat
271 fcat :: [Doc] -> Doc; -- ^ \"Paragraph fill\" version of cat
272 fsep :: [Doc] -> Doc; -- ^ \"Paragraph fill\" version of sep
274 nest :: Int -> Doc -> Doc; -- ^ Nested
277 -- GHC-specific ones.
279 hang :: Doc -> Int -> Doc -> Doc; -- ^ @hang d1 n d2 = sep [d1, nest n d2]@
280 punctuate :: Doc -> [Doc] -> [Doc]; -- ^ @punctuate p [d1, ... dn] = [d1 \<> p, d2 \<> p, ... dn-1 \<> p, dn]@
283 -- Displaying @Doc@ values.
285 instance Show Doc where
286 showsPrec prec doc cont = showDoc doc cont
288 -- | Renders the document as a string using the default style
289 render :: Doc -> String
291 -- | The general rendering interface
292 fullRender :: Mode -- ^Rendering mode
293 -> Int -- ^Line length
294 -> Float -- ^Ribbons per line
295 -> (TextDetails -> a -> a) -- ^What to do with text
296 -> a -- ^What to do at the end
297 -> Doc -- ^The document
300 -- | Render the document as a string using a specified style
301 renderStyle :: Style -> Doc -> String
303 -- | A rendering style
305 = Style { mode :: Mode -- ^ The rendering mode
306 , lineLength :: Int -- ^ Length of line, in chars
307 , ribbonsPerLine :: Float -- ^ Ratio of ribbon length to line length
310 -- | The default style (@mode=PageMode, lineLength=100, ribbonsPerLine=1.5@)
312 style = Style { lineLength = 100, ribbonsPerLine = 1.5, mode = PageMode }
315 data Mode = PageMode -- ^Normal
316 | ZigZagMode -- ^With zig-zag cuts
317 | LeftMode -- ^No indentation, infinitely long lines
318 | OneLineMode -- ^All on one line
320 -- ---------------------------------------------------------------------------
323 -- The Doc combinators satisfy the following laws:
328 <a1> (x $$ y) $$ z = x $$ (y $$ z)
336 <b1> (x <> y) <> z = x <> (y <> z)
337 <b2> empty <> x = empty
344 <t1> text s <> text t = text (s++t)
345 <t2> text "" <> x = x, if x non-empty
350 <n2> nest k (nest k' x) = nest (k+k') x
351 <n3> nest k (x <> y) = nest k z <> nest k y
352 <n4> nest k (x $$ y) = nest k x $$ nest k y
353 <n5> nest k empty = empty
354 <n6> x <> nest k y = x <> y, if x non-empty
356 ** Note the side condition on <n6>! It is this that
357 ** makes it OK for empty to be a left unit for <>.
361 <m1> (text s <> x) $$ y = text s <> ((text "" <> x)) $$
364 <m2> (x $$ y) <> z = x $$ (y <> z)
368 Laws for list versions
369 ~~~~~~~~~~~~~~~~~~~~~~
370 <l1> sep (ps++[empty]++qs) = sep (ps ++ qs)
371 ...ditto hsep, hcat, vcat, fill...
373 <l2> nest k (sep ps) = sep (map (nest k) ps)
374 ...ditto hsep, hcat, vcat, fill...
378 <o1> oneLiner (nest k p) = nest k (oneLiner p)
379 <o2> oneLiner (x <> y) = oneLiner x <> oneLiner y
381 You might think that the following verion of <m1> would
384 <3 NO> (text s <> x) $$ y = text s <> ((empty <> x)) $$
387 But it doesn't work, for if x=empty, we would have
389 text s $$ y = text s <> (empty $$ nest (-length s) y)
390 = text s <> nest (-length s) y
393 -- ---------------------------------------------------------------------------
394 -- Simple derived definitions
408 int n = text (show n)
409 integer n = text (show n)
410 float n = text (show n)
411 double n = text (show n)
412 rational n = text (show n)
413 -- SIGBJORN wrote instead:
414 -- rational n = text (show (fromRationalX n))
416 quotes p = char '\'' <> p <> char '\''
417 doubleQuotes p = char '"' <> p <> char '"'
418 parens p = char '(' <> p <> char ')'
419 brackets p = char '[' <> p <> char ']'
420 braces p = char '{' <> p <> char '}'
423 hcat = foldr (<>) empty
424 hsep = foldr (<+>) empty
425 vcat = foldr ($$) empty
427 hang d1 n d2 = sep [d1, nest n d2]
430 punctuate p (d:ds) = go d ds
433 go d (e:es) = (d <> p) : go e es
435 -- ---------------------------------------------------------------------------
438 -- A Doc represents a *set* of layouts. A Doc with
439 -- no occurrences of Union or NoDoc represents just one layout.
441 -- | The abstract type of documents
444 | NilAbove Doc -- text "" $$ x
445 | TextBeside TextDetails !Int Doc -- text s <> x
446 | Nest !Int Doc -- nest k x
447 | Union Doc Doc -- ul `union` ur
448 | NoDoc -- The empty set of documents
449 | Beside Doc Bool Doc -- True <=> space between
450 | Above Doc Bool Doc -- True <=> never overlap
452 type RDoc = Doc -- RDoc is a "reduced Doc", guaranteed not to have a top-level Above or Beside
455 reduceDoc :: Doc -> RDoc
456 reduceDoc (Beside p g q) = beside p g (reduceDoc q)
457 reduceDoc (Above p g q) = above p g (reduceDoc q)
461 data TextDetails = Chr Char
468 Here are the invariants:
470 * The argument of NilAbove is never Empty. Therefore
471 a NilAbove occupies at least two lines.
473 * The arugment of @TextBeside@ is never @Nest@.
476 * The layouts of the two arguments of @Union@ both flatten to the same
479 * The arguments of @Union@ are either @TextBeside@, or @NilAbove@.
481 * The right argument of a union cannot be equivalent to the empty set
482 (@NoDoc@). If the left argument of a union is equivalent to the
483 empty set (@NoDoc@), then the @NoDoc@ appears in the first line.
485 * An empty document is always represented by @Empty@. It can't be
486 hidden inside a @Nest@, or a @Union@ of two @Empty@s.
488 * The first line of every layout in the left argument of @Union@ is
489 longer than the first line of any layout in the right argument.
490 (1) ensures that the left argument has a first line. In view of
491 (3), this invariant means that the right argument must have at
495 -- Arg of a NilAbove is always an RDoc
496 nilAbove_ p = NilAbove p
498 -- Arg of a TextBeside is always an RDoc
499 textBeside_ s sl p = TextBeside s sl p
501 -- Arg of Nest is always an RDoc
504 -- Args of union are always RDocs
505 union_ p q = Union p q
508 -- Notice the difference between
509 -- * NoDoc (no documents)
510 -- * Empty (one empty document; no height and no width)
511 -- * text "" (a document containing the empty string;
512 -- one line high, but has no width)
515 -- ---------------------------------------------------------------------------
516 -- @empty@, @text@, @nest@, @union@
523 char c = textBeside_ (Chr c) 1 Empty
524 text s = case length s of {sl -> textBeside_ (Str s) sl Empty}
525 ptext s = case length s of {sl -> textBeside_ (PStr s) sl Empty}
527 nest k p = mkNest k (reduceDoc p) -- Externally callable version
529 -- mkNest checks for Nest's invariant that it doesn't have an Empty inside it
530 mkNest k _ | k `seq` False = undefined
531 mkNest k (Nest k1 p) = mkNest (k + k1) p
532 mkNest k NoDoc = NoDoc
533 mkNest k Empty = Empty
534 mkNest 0 p = p -- Worth a try!
535 mkNest k p = nest_ k p
537 -- mkUnion checks for an empty document
538 mkUnion Empty q = Empty
539 mkUnion p q = p `union_` q
541 -- ---------------------------------------------------------------------------
542 -- Vertical composition @$$@
544 p $$ q = Above p False q
545 p $+$ q = Above p True q
547 above :: Doc -> Bool -> RDoc -> RDoc
548 above (Above p g1 q1) g2 q2 = above p g1 (above q1 g2 q2)
549 above p@(Beside _ _ _) g q = aboveNest (reduceDoc p) g 0 (reduceDoc q)
550 above p g q = aboveNest p g 0 (reduceDoc q)
552 aboveNest :: RDoc -> Bool -> Int -> RDoc -> RDoc
553 -- Specfication: aboveNest p g k q = p $g$ (nest k q)
555 aboveNest _ _ k _ | k `seq` False = undefined
556 aboveNest NoDoc g k q = NoDoc
557 aboveNest (p1 `Union` p2) g k q = aboveNest p1 g k q `union_`
560 aboveNest Empty g k q = mkNest k q
561 aboveNest (Nest k1 p) g k q = nest_ k1 (aboveNest p g (k - k1) q)
562 -- p can't be Empty, so no need for mkNest
564 aboveNest (NilAbove p) g k q = nilAbove_ (aboveNest p g k q)
565 aboveNest (TextBeside s sl p) g k q = k1 `seq` textBeside_ s sl rest
569 Empty -> nilAboveNest g k1 q
570 other -> aboveNest p g k1 q
573 nilAboveNest :: Bool -> Int -> RDoc -> RDoc
574 -- Specification: text s <> nilaboveNest g k q
575 -- = text s <> (text "" $g$ nest k q)
577 nilAboveNest _ k _ | k `seq` False = undefined
578 nilAboveNest g k Empty = Empty -- Here's why the "text s <>" is in the spec!
579 nilAboveNest g k (Nest k1 q) = nilAboveNest g (k + k1) q
581 nilAboveNest g k q | (not g) && (k > 0) -- No newline if no overlap
582 = textBeside_ (Str (spaces k)) k q
583 | otherwise -- Put them really above
584 = nilAbove_ (mkNest k q)
586 -- ---------------------------------------------------------------------------
587 -- Horizontal composition @<>@
589 p <> q = Beside p False q
590 p <+> q = Beside p True q
592 beside :: Doc -> Bool -> RDoc -> RDoc
593 -- Specification: beside g p q = p <g> q
595 beside NoDoc g q = NoDoc
596 beside (p1 `Union` p2) g q = (beside p1 g q) `union_` (beside p2 g q)
598 beside (Nest k p) g q = nest_ k (beside p g q) -- p non-empty
599 beside p@(Beside p1 g1 q1) g2 q2
600 {- (A `op1` B) `op2` C == A `op1` (B `op2` C) iff op1 == op2
601 [ && (op1 == <> || op1 == <+>) ] -}
602 | g1 == g2 = beside p1 g1 (beside q1 g2 q2)
603 | otherwise = beside (reduceDoc p) g2 q2
604 beside p@(Above _ _ _) g q = beside (reduceDoc p) g q
605 beside (NilAbove p) g q = nilAbove_ (beside p g q)
606 beside (TextBeside s sl p) g q = textBeside_ s sl rest
609 Empty -> nilBeside g q
610 other -> beside p g q
613 nilBeside :: Bool -> RDoc -> RDoc
614 -- Specification: text "" <> nilBeside g p
617 nilBeside g Empty = Empty -- Hence the text "" in the spec
618 nilBeside g (Nest _ p) = nilBeside g p
619 nilBeside g p | g = textBeside_ space_text 1 p
622 -- ---------------------------------------------------------------------------
623 -- Separate, @sep@, Hughes version
625 -- Specification: sep ps = oneLiner (hsep ps)
629 sep = sepX True -- Separate with spaces
630 cat = sepX False -- Don't
633 sepX x (p:ps) = sep1 x (reduceDoc p) 0 ps
636 -- Specification: sep1 g k ys = sep (x : map (nest k) ys)
637 -- = oneLiner (x <g> nest k (hsep ys))
638 -- `union` x $$ nest k (vcat ys)
640 sep1 :: Bool -> RDoc -> Int -> [Doc] -> RDoc
641 sep1 g _ k ys | k `seq` False = undefined
642 sep1 g NoDoc k ys = NoDoc
643 sep1 g (p `Union` q) k ys = sep1 g p k ys
645 (aboveNest q False k (reduceDoc (vcat ys)))
647 sep1 g Empty k ys = mkNest k (sepX g ys)
648 sep1 g (Nest n p) k ys = nest_ n (sep1 g p (k - n) ys)
650 sep1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (reduceDoc (vcat ys)))
651 sep1 g (TextBeside s sl p) k ys = textBeside_ s sl (sepNB g p (k - sl) ys)
653 -- Specification: sepNB p k ys = sep1 (text "" <> p) k ys
654 -- Called when we have already found some text in the first item
655 -- We have to eat up nests
657 sepNB g (Nest _ p) k ys = sepNB g p k ys
659 sepNB g Empty k ys = oneLiner (nilBeside g (reduceDoc rest))
661 nilAboveNest False k (reduceDoc (vcat ys))
664 | otherwise = hcat ys
666 sepNB g p k ys = sep1 g p k ys
668 -- ---------------------------------------------------------------------------
677 -- fill (p1:p2:ps) = oneLiner p1 <#> nest (length p1)
678 -- (fill (oneLiner p2 : ps))
683 fill g (p:ps) = fill1 g (reduceDoc p) 0 ps
686 fill1 :: Bool -> RDoc -> Int -> [Doc] -> Doc
687 fill1 g _ k ys | k `seq` False = undefined
688 fill1 g NoDoc k ys = NoDoc
689 fill1 g (p `Union` q) k ys = fill1 g p k ys
691 (aboveNest q False k (fill g ys))
693 fill1 g Empty k ys = mkNest k (fill g ys)
694 fill1 g (Nest n p) k ys = nest_ n (fill1 g p (k - n) ys)
696 fill1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (fill g ys))
697 fill1 g (TextBeside s sl p) k ys = textBeside_ s sl (fillNB g p (k - sl) ys)
699 fillNB g _ k ys | k `seq` False = undefined
700 fillNB g (Nest _ p) k ys = fillNB g p k ys
701 fillNB g Empty k [] = Empty
702 fillNB g Empty k (y:ys) = nilBeside g (fill1 g (oneLiner (reduceDoc y)) k1 ys)
704 nilAboveNest False k (fill g (y:ys))
709 fillNB g p k ys = fill1 g p k ys
712 -- ---------------------------------------------------------------------------
713 -- Selecting the best layout
716 -> Int -- Line length
717 -> Int -- Ribbon length
719 -> RDoc -- No unions in here!
721 best OneLineMode w r p
726 get (NilAbove p) = nilAbove_ (get p)
727 get (TextBeside s sl p) = textBeside_ s sl (get p)
728 get (Nest k p) = get p -- Elide nest
729 get (p `Union` q) = first (get p) (get q)
734 get :: Int -- (Remaining) width of line
736 get w _ | w==0 && False = undefined
739 get w (NilAbove p) = nilAbove_ (get w p)
740 get w (TextBeside s sl p) = textBeside_ s sl (get1 w sl p)
741 get w (Nest k p) = nest_ k (get (w - k) p)
742 get w (p `Union` q) = nicest w r (get w p) (get w q)
744 get1 :: Int -- (Remaining) width of line
745 -> Int -- Amount of first line already eaten up
746 -> Doc -- This is an argument to TextBeside => eat Nests
747 -> Doc -- No unions in here!
749 get1 w _ _ | w==0 && False = undefined
750 get1 w sl Empty = Empty
751 get1 w sl NoDoc = NoDoc
752 get1 w sl (NilAbove p) = nilAbove_ (get (w - sl) p)
753 get1 w sl (TextBeside t tl p) = textBeside_ t tl (get1 w (sl + tl) p)
754 get1 w sl (Nest k p) = get1 w sl p
755 get1 w sl (p `Union` q) = nicest1 w r sl (get1 w sl p)
758 nicest w r p q = nicest1 w r 0 p q
759 nicest1 w r sl p q | fits ((w `minn` r) - sl) p = p
762 fits :: Int -- Space available
764 -> Bool -- True if *first line* of Doc fits in space available
766 fits n p | n < 0 = False
769 fits n (NilAbove _) = True
770 fits n (TextBeside _ sl p) = fits (n - sl) p
775 -- @first@ and @nonEmptySet@ are similar to @nicest@ and @fits@, only simpler.
776 -- @first@ returns its first argument if it is non-empty, otherwise its second.
778 first p q | nonEmptySet p = p
781 nonEmptySet NoDoc = False
782 nonEmptySet (p `Union` q) = True
783 nonEmptySet Empty = True
784 nonEmptySet (NilAbove p) = True -- NoDoc always in first line
785 nonEmptySet (TextBeside _ _ p) = nonEmptySet p
786 nonEmptySet (Nest _ p) = nonEmptySet p
788 -- @oneLiner@ returns the one-line members of the given set of @Doc@s.
790 oneLiner :: Doc -> Doc
791 oneLiner NoDoc = NoDoc
792 oneLiner Empty = Empty
793 oneLiner (NilAbove p) = NoDoc
794 oneLiner (TextBeside s sl p) = textBeside_ s sl (oneLiner p)
795 oneLiner (Nest k p) = nest_ k (oneLiner p)
796 oneLiner (p `Union` q) = oneLiner p
799 -- ---------------------------------------------------------------------------
800 -- Displaying the best layout
802 renderStyle style doc
803 = fullRender (mode style)
805 (ribbonsPerLine style)
810 render doc = showDoc doc ""
811 showDoc doc rest = fullRender PageMode 100 1.5 string_txt rest doc
813 string_txt (Chr c) s = c:s
814 string_txt (Str s1) s2 = s1 ++ s2
815 string_txt (PStr s1) s2 = s1 ++ s2
818 fullRender OneLineMode _ _ txt end doc = easy_display space_text txt end (reduceDoc doc)
819 fullRender LeftMode _ _ txt end doc = easy_display nl_text txt end (reduceDoc doc)
821 fullRender mode line_length ribbons_per_line txt end doc
822 = display mode line_length ribbon_length txt end best_doc
824 best_doc = best mode hacked_line_length ribbon_length (reduceDoc doc)
826 hacked_line_length, ribbon_length :: Int
827 ribbon_length = round (fromIntegral line_length / ribbons_per_line)
828 hacked_line_length = case mode of { ZigZagMode -> maxBound; other -> line_length }
830 display mode page_width ribbon_width txt end doc
831 = case page_width - ribbon_width of { gap_width ->
832 case gap_width `quot` 2 of { shift ->
834 lay k _ | k `seq` False = undefined
835 lay k (Nest k1 p) = lay (k + k1) p
838 lay k (NilAbove p) = nl_text `txt` lay k p
840 lay k (TextBeside s sl p)
842 ZigZagMode | k >= gap_width
844 Str (multi_ch shift '/') `txt` (
846 lay1 (k - shift) s sl p)))
850 Str (multi_ch shift '\\') `txt` (
852 lay1 (k + shift) s sl p )))
854 other -> lay1 k s sl p
856 lay1 k _ sl _ | k+sl `seq` False = undefined
857 lay1 k s sl p = Str (indent k) `txt` (s `txt` lay2 (k + sl) p)
859 lay2 k _ | k `seq` False = undefined
860 lay2 k (NilAbove p) = nl_text `txt` lay k p
861 lay2 k (TextBeside s sl p) = s `txt` (lay2 (k + sl) p)
862 lay2 k (Nest _ p) = lay2 k p
868 cant_fail = error "easy_display: NoDoc"
869 easy_display nl_text txt end doc
872 lay NoDoc no_doc = no_doc
873 lay (Union p q) no_doc = {- lay p -} (lay q cant_fail) -- Second arg can't be NoDoc
874 lay (Nest k p) no_doc = lay p no_doc
875 lay Empty no_doc = end
876 lay (NilAbove p) no_doc = nl_text `txt` lay p cant_fail -- NoDoc always on first line
877 lay (TextBeside s sl p) no_doc = s `txt` lay p no_doc
879 -- OLD version: we shouldn't rely on tabs being 8 columns apart in the output.
880 -- indent n | n >= 8 = '\t' : indent (n - 8)
881 -- | otherwise = spaces n
885 multi_ch n ch = ch : multi_ch (n - 1) ch
887 -- (spaces n) generates a list of n spaces
889 -- It should never be called with 'n' < 0, but that can happen for reasons I don't understand
890 -- Here's a test case:
891 -- ncat x y = nest 4 $ cat [ x, y ]
892 -- d1 = foldl1 ncat $ take 50 $ repeat $ char 'a'
893 -- d2 = parens $ sep [ d1, text "+" , d1 ]
895 -- I don't feel motivated enough to find the Real Bug, so meanwhile we just test for n<=0
896 spaces n | n <= 0 = ""
897 | otherwise = ' ' : spaces (n - 1)
899 {- Comments from Johannes Waldmann about what the problem might be:
901 In the example above, d2 and d1 are deeply nested, but `text "+"' is not,
902 so the layout function tries to "out-dent" it.
904 when I look at the Doc values that are generated, there are lots of
905 Nest constructors with negative arguments. see this sample output of
906 d1 (obtained with hugs, :s -u)
908 tBeside (TextDetails_Chr 'a') 1 Doc_Empty) (Doc_NilAbove (Doc_Nest
909 (-241) (Doc_TextBeside (TextDetails_Chr 'a') 1 Doc_Empty)))))
910 (Doc_NilAbove (Doc_Nest (-236) (Doc_TextBeside (TextDetails_Chr 'a') 1
911 (Doc_NilAbove (Doc_Nest (-5) (Doc_TextBeside (TextDetails_Chr 'a') 1
912 Doc_Empty)))))))) (Doc_NilAbove (Doc_Nest (-231) (Doc_TextBeside
913 (TextDetails_Chr 'a') 1 (Doc_NilAbove (Doc_Nest (-5) (Doc_TextBeside
914 (TextDetails_Chr 'a') 1 (Doc_NilAbove (Doc_Nest (-5) (Doc_TextBeside
915 (TextDetails_Chr 'a') 1 Doc_Empty))))))))))) (Doc_NilAbove (Doc_Nest