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 (text "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 -- * Constructing documents
176 -- ** Converting values into documents
178 int, integer, float, double, rational,
180 -- ** Simple derived documents
181 semi, comma, colon, space, equals,
182 lparen, rparen, lbrack, rbrack, lbrace, rbrace,
184 -- ** Wrapping documents in delimiters
185 parens, brackets, braces, quotes, doubleQuotes,
187 -- ** Combining documents
189 (<>), (<+>), hcat, hsep,
196 -- * Predicates on documents
199 -- * Rendering documents
201 -- ** Default rendering
204 -- ** Rendering with a particular style
209 -- ** General rendering
211 Mode(..), TextDetails(..),
222 -- ---------------------------------------------------------------------------
225 -- The primitive Doc values
227 isEmpty :: Doc -> Bool; -- ^ Returns 'True' if the document is empty
229 -- | The empty document, with no height and no width.
230 -- 'empty' is the identity for '<>', '<+>', '$$' and '$+$', and anywhere
231 -- in the argument list for 'sep', 'hcat', 'hsep', 'vcat', 'fcat' etc.
234 semi :: Doc; -- ^ A ';' character
235 comma :: Doc; -- ^ A ',' character
236 colon :: Doc; -- ^ A ':' character
237 space :: Doc; -- ^ A space character
238 equals :: Doc; -- ^ A '=' character
239 lparen :: Doc; -- ^ A '(' character
240 rparen :: Doc; -- ^ A ')' character
241 lbrack :: Doc; -- ^ A '[' character
242 rbrack :: Doc; -- ^ A ']' character
243 lbrace :: Doc; -- ^ A '{' character
244 rbrace :: Doc; -- ^ A '}' character
246 -- | A document of height and width 1, containing a literal character.
249 -- | A document of height 1 containing a literal string.
250 -- 'text' satisfies the following laws:
252 -- * @'text' s '<>' 'text' t = 'text' (s'++'t)@
254 -- * @'text' \"\" '<>' x = x@, if @x@ non-empty
256 -- The side condition on the last law is necessary because @'text' \"\"@
257 -- has height 1, while 'empty' has no height.
258 text :: String -> Doc
260 -- | An obsolete function, now identical to 'text'.
261 ptext :: String -> Doc
263 int :: Int -> Doc; -- ^ @int n = text (show n)@
264 integer :: Integer -> Doc; -- ^ @integer n = text (show n)@
265 float :: Float -> Doc; -- ^ @float n = text (show n)@
266 double :: Double -> Doc; -- ^ @double n = text (show n)@
267 rational :: Rational -> Doc; -- ^ @rational n = text (show n)@
269 parens :: Doc -> Doc; -- ^ Wrap document in @(...)@
270 brackets :: Doc -> Doc; -- ^ Wrap document in @[...]@
271 braces :: Doc -> Doc; -- ^ Wrap document in @{...}@
272 quotes :: Doc -> Doc; -- ^ Wrap document in @\'...\'@
273 doubleQuotes :: Doc -> Doc; -- ^ Wrap document in @\"...\"@
275 -- Combining @Doc@ values
278 -- '<>' is associative, with identity 'empty'.
279 (<>) :: Doc -> Doc -> Doc
281 -- | Beside, separated by space, unless one of the arguments is 'empty'.
282 -- '<+>' is associative, with identity 'empty'.
283 (<+>) :: Doc -> Doc -> Doc
285 -- | Above, except that if the last line of the first argument stops
286 -- at least one position before the first line of the second begins,
287 -- these two lines are overlapped. For example:
289 -- > text "hi" $$ nest 5 (text "there")
300 -- '$$' is associative, with identity 'empty', and also satisfies
302 -- * @(x '$$' y) '<>' z = x '$$' (y '<>' z)@, if @y@ non-empty.
304 ($$) :: Doc -> Doc -> Doc
306 -- | Above, with no overlapping.
307 -- '$+$' is associative, with identity 'empty'.
308 ($+$) :: Doc -> Doc -> Doc
310 hcat :: [Doc] -> Doc; -- ^List version of '<>'.
311 hsep :: [Doc] -> Doc; -- ^List version of '<+>'.
312 vcat :: [Doc] -> Doc; -- ^List version of '$$'.
314 cat :: [Doc] -> Doc; -- ^ Either 'hcat' or 'vcat'.
315 sep :: [Doc] -> Doc; -- ^ Either 'hsep' or 'vcat'.
316 fcat :: [Doc] -> Doc; -- ^ \"Paragraph fill\" version of 'cat'.
317 fsep :: [Doc] -> Doc; -- ^ \"Paragraph fill\" version of 'sep'.
319 -- | Nest (or indent) a document by a given number of positions
320 -- (which may also be negative). 'nest' satisfies the laws:
322 -- * @'nest' 0 x = x@
324 -- * @'nest' k ('nest' k' x) = 'nest' (k+k') x@
326 -- * @'nest' k (x '<>' y) = 'nest' k z '<>' 'nest' k y@
328 -- * @'nest' k (x '$$' y) = 'nest' k x '$$' 'nest' k y@
330 -- * @'nest' k 'empty' = 'empty'@
332 -- * @x '<>' 'nest' k y = x '<>' y@, if @x@ non-empty
334 -- The side condition on the last law is needed because
335 -- 'empty' is a left identity for '<>'.
336 nest :: Int -> Doc -> Doc
338 -- GHC-specific ones.
340 -- | @hang d1 n d2 = sep [d1, nest n d2]@
341 hang :: Doc -> Int -> Doc -> Doc
343 -- | @punctuate p [d1, ... dn] = [d1 \<> p, d2 \<> p, ... dn-1 \<> p, dn]@
344 punctuate :: Doc -> [Doc] -> [Doc]
347 -- Displaying @Doc@ values.
349 instance Show Doc where
350 showsPrec prec doc cont = showDoc doc cont
352 -- | Renders the document as a string using the default 'style'.
353 render :: Doc -> String
355 -- | The general rendering interface.
356 fullRender :: Mode -- ^Rendering mode
357 -> Int -- ^Line length
358 -> Float -- ^Ribbons per line
359 -> (TextDetails -> a -> a) -- ^What to do with text
360 -> a -- ^What to do at the end
361 -> Doc -- ^The document
364 -- | Render the document as a string using a specified style.
365 renderStyle :: Style -> Doc -> String
367 -- | A rendering style.
369 = Style { mode :: Mode -- ^ The rendering mode
370 , lineLength :: Int -- ^ Length of line, in chars
371 , ribbonsPerLine :: Float -- ^ Ratio of ribbon length to line length
374 -- | The default style (@mode=PageMode, lineLength=100, ribbonsPerLine=1.5@).
376 style = Style { lineLength = 100, ribbonsPerLine = 1.5, mode = PageMode }
379 data Mode = PageMode -- ^Normal
380 | ZigZagMode -- ^With zig-zag cuts
381 | LeftMode -- ^No indentation, infinitely long lines
382 | OneLineMode -- ^All on one line
384 -- ---------------------------------------------------------------------------
387 -- The Doc combinators satisfy the following laws:
392 <a1> (x $$ y) $$ z = x $$ (y $$ z)
400 <b1> (x <> y) <> z = x <> (y <> z)
401 <b2> empty <> x = empty
408 <t1> text s <> text t = text (s++t)
409 <t2> text "" <> x = x, if x non-empty
414 <n2> nest k (nest k' x) = nest (k+k') x
415 <n3> nest k (x <> y) = nest k z <> nest k y
416 <n4> nest k (x $$ y) = nest k x $$ nest k y
417 <n5> nest k empty = empty
418 <n6> x <> nest k y = x <> y, if x non-empty
420 ** Note the side condition on <n6>! It is this that
421 ** makes it OK for empty to be a left unit for <>.
425 <m1> (text s <> x) $$ y = text s <> ((text "" <> x)) $$
428 <m2> (x $$ y) <> z = x $$ (y <> z)
432 Laws for list versions
433 ~~~~~~~~~~~~~~~~~~~~~~
434 <l1> sep (ps++[empty]++qs) = sep (ps ++ qs)
435 ...ditto hsep, hcat, vcat, fill...
437 <l2> nest k (sep ps) = sep (map (nest k) ps)
438 ...ditto hsep, hcat, vcat, fill...
442 <o1> oneLiner (nest k p) = nest k (oneLiner p)
443 <o2> oneLiner (x <> y) = oneLiner x <> oneLiner y
445 You might think that the following verion of <m1> would
448 <3 NO> (text s <> x) $$ y = text s <> ((empty <> x)) $$
451 But it doesn't work, for if x=empty, we would have
453 text s $$ y = text s <> (empty $$ nest (-length s) y)
454 = text s <> nest (-length s) y
457 -- ---------------------------------------------------------------------------
458 -- Simple derived definitions
472 int n = text (show n)
473 integer n = text (show n)
474 float n = text (show n)
475 double n = text (show n)
476 rational n = text (show n)
477 -- SIGBJORN wrote instead:
478 -- rational n = text (show (fromRationalX n))
480 quotes p = char '\'' <> p <> char '\''
481 doubleQuotes p = char '"' <> p <> char '"'
482 parens p = char '(' <> p <> char ')'
483 brackets p = char '[' <> p <> char ']'
484 braces p = char '{' <> p <> char '}'
487 hcat = foldr (<>) empty
488 hsep = foldr (<+>) empty
489 vcat = foldr ($$) empty
491 hang d1 n d2 = sep [d1, nest n d2]
494 punctuate p (d:ds) = go d ds
497 go d (e:es) = (d <> p) : go e es
499 -- ---------------------------------------------------------------------------
502 -- A Doc represents a *set* of layouts. A Doc with
503 -- no occurrences of Union or NoDoc represents just one layout.
505 -- | The abstract type of documents.
506 -- The 'Show' instance is equivalent to using 'render'.
509 | NilAbove Doc -- text "" $$ x
510 | TextBeside TextDetails !Int Doc -- text s <> x
511 | Nest !Int Doc -- nest k x
512 | Union Doc Doc -- ul `union` ur
513 | NoDoc -- The empty set of documents
514 | Beside Doc Bool Doc -- True <=> space between
515 | Above Doc Bool Doc -- True <=> never overlap
517 type RDoc = Doc -- RDoc is a "reduced Doc", guaranteed not to have a top-level Above or Beside
520 reduceDoc :: Doc -> RDoc
521 reduceDoc (Beside p g q) = beside p g (reduceDoc q)
522 reduceDoc (Above p g q) = above p g (reduceDoc q)
526 data TextDetails = Chr Char
533 Here are the invariants:
535 * The argument of NilAbove is never Empty. Therefore
536 a NilAbove occupies at least two lines.
538 * The arugment of @TextBeside@ is never @Nest@.
541 * The layouts of the two arguments of @Union@ both flatten to the same
544 * The arguments of @Union@ are either @TextBeside@, or @NilAbove@.
546 * The right argument of a union cannot be equivalent to the empty set
547 (@NoDoc@). If the left argument of a union is equivalent to the
548 empty set (@NoDoc@), then the @NoDoc@ appears in the first line.
550 * An empty document is always represented by @Empty@. It can't be
551 hidden inside a @Nest@, or a @Union@ of two @Empty@s.
553 * The first line of every layout in the left argument of @Union@ is
554 longer than the first line of any layout in the right argument.
555 (1) ensures that the left argument has a first line. In view of
556 (3), this invariant means that the right argument must have at
560 -- Arg of a NilAbove is always an RDoc
561 nilAbove_ p = NilAbove p
563 -- Arg of a TextBeside is always an RDoc
564 textBeside_ s sl p = TextBeside s sl p
566 -- Arg of Nest is always an RDoc
569 -- Args of union are always RDocs
570 union_ p q = Union p q
573 -- Notice the difference between
574 -- * NoDoc (no documents)
575 -- * Empty (one empty document; no height and no width)
576 -- * text "" (a document containing the empty string;
577 -- one line high, but has no width)
580 -- ---------------------------------------------------------------------------
581 -- @empty@, @text@, @nest@, @union@
588 char c = textBeside_ (Chr c) 1 Empty
589 text s = case length s of {sl -> textBeside_ (Str s) sl Empty}
590 ptext s = case length s of {sl -> textBeside_ (PStr s) sl Empty}
592 nest k p = mkNest k (reduceDoc p) -- Externally callable version
594 -- mkNest checks for Nest's invariant that it doesn't have an Empty inside it
595 mkNest k _ | k `seq` False = undefined
596 mkNest k (Nest k1 p) = mkNest (k + k1) p
597 mkNest k NoDoc = NoDoc
598 mkNest k Empty = Empty
599 mkNest 0 p = p -- Worth a try!
600 mkNest k p = nest_ k p
602 -- mkUnion checks for an empty document
603 mkUnion Empty q = Empty
604 mkUnion p q = p `union_` q
606 -- ---------------------------------------------------------------------------
607 -- Vertical composition @$$@
609 p $$ q = Above p False q
610 p $+$ q = Above p True q
612 above :: Doc -> Bool -> RDoc -> RDoc
613 above (Above p g1 q1) g2 q2 = above p g1 (above q1 g2 q2)
614 above p@(Beside _ _ _) g q = aboveNest (reduceDoc p) g 0 (reduceDoc q)
615 above p g q = aboveNest p g 0 (reduceDoc q)
617 aboveNest :: RDoc -> Bool -> Int -> RDoc -> RDoc
618 -- Specfication: aboveNest p g k q = p $g$ (nest k q)
620 aboveNest _ _ k _ | k `seq` False = undefined
621 aboveNest NoDoc g k q = NoDoc
622 aboveNest (p1 `Union` p2) g k q = aboveNest p1 g k q `union_`
625 aboveNest Empty g k q = mkNest k q
626 aboveNest (Nest k1 p) g k q = nest_ k1 (aboveNest p g (k - k1) q)
627 -- p can't be Empty, so no need for mkNest
629 aboveNest (NilAbove p) g k q = nilAbove_ (aboveNest p g k q)
630 aboveNest (TextBeside s sl p) g k q = k1 `seq` textBeside_ s sl rest
634 Empty -> nilAboveNest g k1 q
635 other -> aboveNest p g k1 q
638 nilAboveNest :: Bool -> Int -> RDoc -> RDoc
639 -- Specification: text s <> nilaboveNest g k q
640 -- = text s <> (text "" $g$ nest k q)
642 nilAboveNest _ k _ | k `seq` False = undefined
643 nilAboveNest g k Empty = Empty -- Here's why the "text s <>" is in the spec!
644 nilAboveNest g k (Nest k1 q) = nilAboveNest g (k + k1) q
646 nilAboveNest g k q | (not g) && (k > 0) -- No newline if no overlap
647 = textBeside_ (Str (spaces k)) k q
648 | otherwise -- Put them really above
649 = nilAbove_ (mkNest k q)
651 -- ---------------------------------------------------------------------------
652 -- Horizontal composition @<>@
654 p <> q = Beside p False q
655 p <+> q = Beside p True q
657 beside :: Doc -> Bool -> RDoc -> RDoc
658 -- Specification: beside g p q = p <g> q
660 beside NoDoc g q = NoDoc
661 beside (p1 `Union` p2) g q = (beside p1 g q) `union_` (beside p2 g q)
663 beside (Nest k p) g q = nest_ k (beside p g q) -- p non-empty
664 beside p@(Beside p1 g1 q1) g2 q2
665 {- (A `op1` B) `op2` C == A `op1` (B `op2` C) iff op1 == op2
666 [ && (op1 == <> || op1 == <+>) ] -}
667 | g1 == g2 = beside p1 g1 (beside q1 g2 q2)
668 | otherwise = beside (reduceDoc p) g2 q2
669 beside p@(Above _ _ _) g q = beside (reduceDoc p) g q
670 beside (NilAbove p) g q = nilAbove_ (beside p g q)
671 beside (TextBeside s sl p) g q = textBeside_ s sl rest
674 Empty -> nilBeside g q
675 other -> beside p g q
678 nilBeside :: Bool -> RDoc -> RDoc
679 -- Specification: text "" <> nilBeside g p
682 nilBeside g Empty = Empty -- Hence the text "" in the spec
683 nilBeside g (Nest _ p) = nilBeside g p
684 nilBeside g p | g = textBeside_ space_text 1 p
687 -- ---------------------------------------------------------------------------
688 -- Separate, @sep@, Hughes version
690 -- Specification: sep ps = oneLiner (hsep ps)
694 sep = sepX True -- Separate with spaces
695 cat = sepX False -- Don't
698 sepX x (p:ps) = sep1 x (reduceDoc p) 0 ps
701 -- Specification: sep1 g k ys = sep (x : map (nest k) ys)
702 -- = oneLiner (x <g> nest k (hsep ys))
703 -- `union` x $$ nest k (vcat ys)
705 sep1 :: Bool -> RDoc -> Int -> [Doc] -> RDoc
706 sep1 g _ k ys | k `seq` False = undefined
707 sep1 g NoDoc k ys = NoDoc
708 sep1 g (p `Union` q) k ys = sep1 g p k ys
710 (aboveNest q False k (reduceDoc (vcat ys)))
712 sep1 g Empty k ys = mkNest k (sepX g ys)
713 sep1 g (Nest n p) k ys = nest_ n (sep1 g p (k - n) ys)
715 sep1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (reduceDoc (vcat ys)))
716 sep1 g (TextBeside s sl p) k ys = textBeside_ s sl (sepNB g p (k - sl) ys)
718 -- Specification: sepNB p k ys = sep1 (text "" <> p) k ys
719 -- Called when we have already found some text in the first item
720 -- We have to eat up nests
722 sepNB g (Nest _ p) k ys = sepNB g p k ys
724 sepNB g Empty k ys = oneLiner (nilBeside g (reduceDoc rest))
726 nilAboveNest False k (reduceDoc (vcat ys))
729 | otherwise = hcat ys
731 sepNB g p k ys = sep1 g p k ys
733 -- ---------------------------------------------------------------------------
742 -- fill (p1:p2:ps) = oneLiner p1 <#> nest (length p1)
743 -- (fill (oneLiner p2 : ps))
748 fill g (p:ps) = fill1 g (reduceDoc p) 0 ps
751 fill1 :: Bool -> RDoc -> Int -> [Doc] -> Doc
752 fill1 g _ k ys | k `seq` False = undefined
753 fill1 g NoDoc k ys = NoDoc
754 fill1 g (p `Union` q) k ys = fill1 g p k ys
756 (aboveNest q False k (fill g ys))
758 fill1 g Empty k ys = mkNest k (fill g ys)
759 fill1 g (Nest n p) k ys = nest_ n (fill1 g p (k - n) ys)
761 fill1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (fill g ys))
762 fill1 g (TextBeside s sl p) k ys = textBeside_ s sl (fillNB g p (k - sl) ys)
764 fillNB g _ k ys | k `seq` False = undefined
765 fillNB g (Nest _ p) k ys = fillNB g p k ys
766 fillNB g Empty k [] = Empty
767 fillNB g Empty k (y:ys) = nilBeside g (fill1 g (oneLiner (reduceDoc y)) k1 ys)
769 nilAboveNest False k (fill g (y:ys))
774 fillNB g p k ys = fill1 g p k ys
777 -- ---------------------------------------------------------------------------
778 -- Selecting the best layout
781 -> Int -- Line length
782 -> Int -- Ribbon length
784 -> RDoc -- No unions in here!
786 best OneLineMode w r p
791 get (NilAbove p) = nilAbove_ (get p)
792 get (TextBeside s sl p) = textBeside_ s sl (get p)
793 get (Nest k p) = get p -- Elide nest
794 get (p `Union` q) = first (get p) (get q)
799 get :: Int -- (Remaining) width of line
801 get w _ | w==0 && False = undefined
804 get w (NilAbove p) = nilAbove_ (get w p)
805 get w (TextBeside s sl p) = textBeside_ s sl (get1 w sl p)
806 get w (Nest k p) = nest_ k (get (w - k) p)
807 get w (p `Union` q) = nicest w r (get w p) (get w q)
809 get1 :: Int -- (Remaining) width of line
810 -> Int -- Amount of first line already eaten up
811 -> Doc -- This is an argument to TextBeside => eat Nests
812 -> Doc -- No unions in here!
814 get1 w _ _ | w==0 && False = undefined
815 get1 w sl Empty = Empty
816 get1 w sl NoDoc = NoDoc
817 get1 w sl (NilAbove p) = nilAbove_ (get (w - sl) p)
818 get1 w sl (TextBeside t tl p) = textBeside_ t tl (get1 w (sl + tl) p)
819 get1 w sl (Nest k p) = get1 w sl p
820 get1 w sl (p `Union` q) = nicest1 w r sl (get1 w sl p)
823 nicest w r p q = nicest1 w r 0 p q
824 nicest1 w r sl p q | fits ((w `minn` r) - sl) p = p
827 fits :: Int -- Space available
829 -> Bool -- True if *first line* of Doc fits in space available
831 fits n p | n < 0 = False
834 fits n (NilAbove _) = True
835 fits n (TextBeside _ sl p) = fits (n - sl) p
840 -- @first@ and @nonEmptySet@ are similar to @nicest@ and @fits@, only simpler.
841 -- @first@ returns its first argument if it is non-empty, otherwise its second.
843 first p q | nonEmptySet p = p
846 nonEmptySet NoDoc = False
847 nonEmptySet (p `Union` q) = True
848 nonEmptySet Empty = True
849 nonEmptySet (NilAbove p) = True -- NoDoc always in first line
850 nonEmptySet (TextBeside _ _ p) = nonEmptySet p
851 nonEmptySet (Nest _ p) = nonEmptySet p
853 -- @oneLiner@ returns the one-line members of the given set of @Doc@s.
855 oneLiner :: Doc -> Doc
856 oneLiner NoDoc = NoDoc
857 oneLiner Empty = Empty
858 oneLiner (NilAbove p) = NoDoc
859 oneLiner (TextBeside s sl p) = textBeside_ s sl (oneLiner p)
860 oneLiner (Nest k p) = nest_ k (oneLiner p)
861 oneLiner (p `Union` q) = oneLiner p
864 -- ---------------------------------------------------------------------------
865 -- Displaying the best layout
867 renderStyle style doc
868 = fullRender (mode style)
870 (ribbonsPerLine style)
875 render doc = showDoc doc ""
876 showDoc doc rest = fullRender PageMode 100 1.5 string_txt rest doc
878 string_txt (Chr c) s = c:s
879 string_txt (Str s1) s2 = s1 ++ s2
880 string_txt (PStr s1) s2 = s1 ++ s2
883 fullRender OneLineMode _ _ txt end doc = easy_display space_text txt end (reduceDoc doc)
884 fullRender LeftMode _ _ txt end doc = easy_display nl_text txt end (reduceDoc doc)
886 fullRender mode line_length ribbons_per_line txt end doc
887 = display mode line_length ribbon_length txt end best_doc
889 best_doc = best mode hacked_line_length ribbon_length (reduceDoc doc)
891 hacked_line_length, ribbon_length :: Int
892 ribbon_length = round (fromIntegral line_length / ribbons_per_line)
893 hacked_line_length = case mode of { ZigZagMode -> maxBound; other -> line_length }
895 display mode page_width ribbon_width txt end doc
896 = case page_width - ribbon_width of { gap_width ->
897 case gap_width `quot` 2 of { shift ->
899 lay k _ | k `seq` False = undefined
900 lay k (Nest k1 p) = lay (k + k1) p
903 lay k (NilAbove p) = nl_text `txt` lay k p
905 lay k (TextBeside s sl p)
907 ZigZagMode | k >= gap_width
909 Str (multi_ch shift '/') `txt` (
911 lay1 (k - shift) s sl p)))
915 Str (multi_ch shift '\\') `txt` (
917 lay1 (k + shift) s sl p )))
919 other -> lay1 k s sl p
921 lay1 k _ sl _ | k+sl `seq` False = undefined
922 lay1 k s sl p = Str (indent k) `txt` (s `txt` lay2 (k + sl) p)
924 lay2 k _ | k `seq` False = undefined
925 lay2 k (NilAbove p) = nl_text `txt` lay k p
926 lay2 k (TextBeside s sl p) = s `txt` (lay2 (k + sl) p)
927 lay2 k (Nest _ p) = lay2 k p
933 cant_fail = error "easy_display: NoDoc"
934 easy_display nl_text txt end doc
937 lay NoDoc no_doc = no_doc
938 lay (Union p q) no_doc = {- lay p -} (lay q cant_fail) -- Second arg can't be NoDoc
939 lay (Nest k p) no_doc = lay p no_doc
940 lay Empty no_doc = end
941 lay (NilAbove p) no_doc = nl_text `txt` lay p cant_fail -- NoDoc always on first line
942 lay (TextBeside s sl p) no_doc = s `txt` lay p no_doc
944 -- OLD version: we shouldn't rely on tabs being 8 columns apart in the output.
945 -- indent n | n >= 8 = '\t' : indent (n - 8)
946 -- | otherwise = spaces n
950 multi_ch n ch = ch : multi_ch (n - 1) ch
952 -- (spaces n) generates a list of n spaces
954 -- It should never be called with 'n' < 0, but that can happen for reasons I don't understand
955 -- Here's a test case:
956 -- ncat x y = nest 4 $ cat [ x, y ]
957 -- d1 = foldl1 ncat $ take 50 $ repeat $ char 'a'
958 -- d2 = parens $ sep [ d1, text "+" , d1 ]
960 -- I don't feel motivated enough to find the Real Bug, so meanwhile we just test for n<=0
961 spaces n | n <= 0 = ""
962 | otherwise = ' ' : spaces (n - 1)
964 {- Comments from Johannes Waldmann about what the problem might be:
966 In the example above, d2 and d1 are deeply nested, but `text "+"' is not,
967 so the layout function tries to "out-dent" it.
969 when I look at the Doc values that are generated, there are lots of
970 Nest constructors with negative arguments. see this sample output of
971 d1 (obtained with hugs, :s -u)
973 tBeside (TextDetails_Chr 'a') 1 Doc_Empty) (Doc_NilAbove (Doc_Nest
974 (-241) (Doc_TextBeside (TextDetails_Chr 'a') 1 Doc_Empty)))))
975 (Doc_NilAbove (Doc_Nest (-236) (Doc_TextBeside (TextDetails_Chr 'a') 1
976 (Doc_NilAbove (Doc_Nest (-5) (Doc_TextBeside (TextDetails_Chr 'a') 1
977 Doc_Empty)))))))) (Doc_NilAbove (Doc_Nest (-231) (Doc_TextBeside
978 (TextDetails_Chr 'a') 1 (Doc_NilAbove (Doc_Nest (-5) (Doc_TextBeside
979 (TextDetails_Chr 'a') 1 (Doc_NilAbove (Doc_Nest (-5) (Doc_TextBeside
980 (TextDetails_Chr 'a') 1 Doc_Empty))))))))))) (Doc_NilAbove (Doc_Nest