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 ($$) :: Doc -> Doc -> Doc; -- ^Above; if there is no
265 -- overlap it \"dovetails\" the two
266 vcat :: [Doc] -> Doc; -- ^List version of '$$'
268 cat :: [Doc] -> Doc; -- ^ Either hcat or vcat
269 sep :: [Doc] -> Doc; -- ^ Either hsep or vcat
270 fcat :: [Doc] -> Doc; -- ^ \"Paragraph fill\" version of cat
271 fsep :: [Doc] -> Doc; -- ^ \"Paragraph fill\" version of sep
273 nest :: Int -> Doc -> Doc; -- ^ Nested
276 -- GHC-specific ones.
278 hang :: Doc -> Int -> Doc -> Doc; -- ^ @hang d1 n d2 = sep [d1, nest n d2]@
279 punctuate :: Doc -> [Doc] -> [Doc]; -- ^ @punctuate p [d1, ... dn] = [d1 \<> p, d2 \<> p, ... dn-1 \<> p, dn]@
282 -- Displaying @Doc@ values.
284 instance Show Doc where
285 showsPrec prec doc cont = showDoc doc cont
287 -- | Renders the document as a string using the default style
288 render :: Doc -> String
290 -- | The general rendering interface
291 fullRender :: Mode -- ^Rendering mode
292 -> Int -- ^Line length
293 -> Float -- ^Ribbons per line
294 -> (TextDetails -> a -> a) -- ^What to do with text
295 -> a -- ^What to do at the end
296 -> Doc -- ^The document
299 -- | Render the document as a string using a specified style
300 renderStyle :: Style -> Doc -> String
302 -- | A rendering style
304 = Style { mode :: Mode -- ^ The rendering mode
305 , lineLength :: Int -- ^ Length of line, in chars
306 , ribbonsPerLine :: Float -- ^ Ratio of ribbon length to line length
309 -- | The default style (@mode=PageMode, lineLength=100, ribbonsPerLine=1.5@)
311 style = Style { lineLength = 100, ribbonsPerLine = 1.5, mode = PageMode }
314 data Mode = PageMode -- ^Normal
315 | ZigZagMode -- ^With zig-zag cuts
316 | LeftMode -- ^No indentation, infinitely long lines
317 | OneLineMode -- ^All on one line
319 -- ---------------------------------------------------------------------------
322 -- The Doc combinators satisfy the following laws:
327 <a1> (x $$ y) $$ z = x $$ (y $$ z)
335 <b1> (x <> y) <> z = x <> (y <> z)
336 <b2> empty <> x = empty
343 <t1> text s <> text t = text (s++t)
344 <t2> text "" <> x = x, if x non-empty
349 <n2> nest k (nest k' x) = nest (k+k') x
350 <n3> nest k (x <> y) = nest k z <> nest k y
351 <n4> nest k (x $$ y) = nest k x $$ nest k y
352 <n5> nest k empty = empty
353 <n6> x <> nest k y = x <> y, if x non-empty
355 ** Note the side condition on <n6>! It is this that
356 ** makes it OK for empty to be a left unit for <>.
360 <m1> (text s <> x) $$ y = text s <> ((text "" <> x)) $$
363 <m2> (x $$ y) <> z = x $$ (y <> z)
367 Laws for list versions
368 ~~~~~~~~~~~~~~~~~~~~~~
369 <l1> sep (ps++[empty]++qs) = sep (ps ++ qs)
370 ...ditto hsep, hcat, vcat, fill...
372 <l2> nest k (sep ps) = sep (map (nest k) ps)
373 ...ditto hsep, hcat, vcat, fill...
377 <o1> oneLiner (nest k p) = nest k (oneLiner p)
378 <o2> oneLiner (x <> y) = oneLiner x <> oneLiner y
380 You might think that the following verion of <m1> would
383 <3 NO> (text s <> x) $$ y = text s <> ((empty <> x)) $$
386 But it doesn't work, for if x=empty, we would have
388 text s $$ y = text s <> (empty $$ nest (-length s) y)
389 = text s <> nest (-length s) y
392 -- ---------------------------------------------------------------------------
393 -- Simple derived definitions
407 int n = text (show n)
408 integer n = text (show n)
409 float n = text (show n)
410 double n = text (show n)
411 rational n = text (show n)
412 -- SIGBJORN wrote instead:
413 -- rational n = text (show (fromRationalX n))
415 quotes p = char '`' <> p <> char '\''
416 doubleQuotes p = char '"' <> p <> char '"'
417 parens p = char '(' <> p <> char ')'
418 brackets p = char '[' <> p <> char ']'
419 braces p = char '{' <> p <> char '}'
422 hcat = foldr (<>) empty
423 hsep = foldr (<+>) empty
424 vcat = foldr ($$) empty
426 hang d1 n d2 = sep [d1, nest n d2]
429 punctuate p (d:ds) = go d ds
432 go d (e:es) = (d <> p) : go e es
434 -- ---------------------------------------------------------------------------
437 -- A Doc represents a *set* of layouts. A Doc with
438 -- no occurrences of Union or NoDoc represents just one layout.
440 -- | The abstract type of documents
443 | NilAbove Doc -- text "" $$ x
444 | TextBeside TextDetails !Int Doc -- text s <> x
445 | Nest !Int Doc -- nest k x
446 | Union Doc Doc -- ul `union` ur
447 | NoDoc -- The empty set of documents
448 | Beside Doc Bool Doc -- True <=> space between
449 | Above Doc Bool Doc -- True <=> never overlap
451 type RDoc = Doc -- RDoc is a "reduced Doc", guaranteed not to have a top-level Above or Beside
454 reduceDoc :: Doc -> RDoc
455 reduceDoc (Beside p g q) = beside p g (reduceDoc q)
456 reduceDoc (Above p g q) = above p g (reduceDoc q)
460 data TextDetails = Chr Char
467 Here are the invariants:
469 * The argument of NilAbove is never Empty. Therefore
470 a NilAbove occupies at least two lines.
472 * The arugment of @TextBeside@ is never @Nest@.
475 * The layouts of the two arguments of @Union@ both flatten to the same
478 * The arguments of @Union@ are either @TextBeside@, or @NilAbove@.
480 * The right argument of a union cannot be equivalent to the empty set
481 (@NoDoc@). If the left argument of a union is equivalent to the
482 empty set (@NoDoc@), then the @NoDoc@ appears in the first line.
484 * An empty document is always represented by @Empty@. It can't be
485 hidden inside a @Nest@, or a @Union@ of two @Empty@s.
487 * The first line of every layout in the left argument of @Union@ is
488 longer than the first line of any layout in the right argument.
489 (1) ensures that the left argument has a first line. In view of
490 (3), this invariant means that the right argument must have at
494 -- Arg of a NilAbove is always an RDoc
495 nilAbove_ p = NilAbove p
497 -- Arg of a TextBeside is always an RDoc
498 textBeside_ s sl p = TextBeside s sl p
500 -- Arg of Nest is always an RDoc
503 -- Args of union are always RDocs
504 union_ p q = Union p q
507 -- Notice the difference between
508 -- * NoDoc (no documents)
509 -- * Empty (one empty document; no height and no width)
510 -- * text "" (a document containing the empty string;
511 -- one line high, but has no width)
514 -- ---------------------------------------------------------------------------
515 -- @empty@, @text@, @nest@, @union@
522 char c = textBeside_ (Chr c) 1 Empty
523 text s = case length s of {sl -> textBeside_ (Str s) sl Empty}
524 ptext s = case length s of {sl -> textBeside_ (PStr s) sl Empty}
526 nest k p = mkNest k (reduceDoc p) -- Externally callable version
528 -- mkNest checks for Nest's invariant that it doesn't have an Empty inside it
529 mkNest k _ | k `seq` False = undefined
530 mkNest k (Nest k1 p) = mkNest (k + k1) p
531 mkNest k NoDoc = NoDoc
532 mkNest k Empty = Empty
533 mkNest 0 p = p -- Worth a try!
534 mkNest k p = nest_ k p
536 -- mkUnion checks for an empty document
537 mkUnion Empty q = Empty
538 mkUnion p q = p `union_` q
540 -- ---------------------------------------------------------------------------
541 -- Vertical composition @$$@
543 p $$ q = Above p False q
544 p $+$ q = Above p True q
546 above :: Doc -> Bool -> RDoc -> RDoc
547 above (Above p g1 q1) g2 q2 = above p g1 (above q1 g2 q2)
548 above p@(Beside _ _ _) g q = aboveNest (reduceDoc p) g 0 (reduceDoc q)
549 above p g q = aboveNest p g 0 (reduceDoc q)
551 aboveNest :: RDoc -> Bool -> Int -> RDoc -> RDoc
552 -- Specfication: aboveNest p g k q = p $g$ (nest k q)
554 aboveNest _ _ k _ | k `seq` False = undefined
555 aboveNest NoDoc g k q = NoDoc
556 aboveNest (p1 `Union` p2) g k q = aboveNest p1 g k q `union_`
559 aboveNest Empty g k q = mkNest k q
560 aboveNest (Nest k1 p) g k q = nest_ k1 (aboveNest p g (k - k1) q)
561 -- p can't be Empty, so no need for mkNest
563 aboveNest (NilAbove p) g k q = nilAbove_ (aboveNest p g k q)
564 aboveNest (TextBeside s sl p) g k q = k1 `seq` textBeside_ s sl rest
568 Empty -> nilAboveNest g k1 q
569 other -> aboveNest p g k1 q
572 nilAboveNest :: Bool -> Int -> RDoc -> RDoc
573 -- Specification: text s <> nilaboveNest g k q
574 -- = text s <> (text "" $g$ nest k q)
576 nilAboveNest _ k _ | k `seq` False = undefined
577 nilAboveNest g k Empty = Empty -- Here's why the "text s <>" is in the spec!
578 nilAboveNest g k (Nest k1 q) = nilAboveNest g (k + k1) q
580 nilAboveNest g k q | (not g) && (k > 0) -- No newline if no overlap
581 = textBeside_ (Str (spaces k)) k q
582 | otherwise -- Put them really above
583 = nilAbove_ (mkNest k q)
585 -- ---------------------------------------------------------------------------
586 -- Horizontal composition @<>@
588 p <> q = Beside p False q
589 p <+> q = Beside p True q
591 beside :: Doc -> Bool -> RDoc -> RDoc
592 -- Specification: beside g p q = p <g> q
594 beside NoDoc g q = NoDoc
595 beside (p1 `Union` p2) g q = (beside p1 g q) `union_` (beside p2 g q)
597 beside (Nest k p) g q = nest_ k (beside p g q) -- p non-empty
598 beside p@(Beside p1 g1 q1) g2 q2
599 {- (A `op1` B) `op2` C == A `op1` (B `op2` C) iff op1 == op2
600 [ && (op1 == <> || op1 == <+>) ] -}
601 | g1 == g2 = beside p1 g1 (beside q1 g2 q2)
602 | otherwise = beside (reduceDoc p) g2 q2
603 beside p@(Above _ _ _) g q = beside (reduceDoc p) g q
604 beside (NilAbove p) g q = nilAbove_ (beside p g q)
605 beside (TextBeside s sl p) g q = textBeside_ s sl rest
608 Empty -> nilBeside g q
609 other -> beside p g q
612 nilBeside :: Bool -> RDoc -> RDoc
613 -- Specification: text "" <> nilBeside g p
616 nilBeside g Empty = Empty -- Hence the text "" in the spec
617 nilBeside g (Nest _ p) = nilBeside g p
618 nilBeside g p | g = textBeside_ space_text 1 p
621 -- ---------------------------------------------------------------------------
622 -- Separate, @sep@, Hughes version
624 -- Specification: sep ps = oneLiner (hsep ps)
628 sep = sepX True -- Separate with spaces
629 cat = sepX False -- Don't
632 sepX x (p:ps) = sep1 x (reduceDoc p) 0 ps
635 -- Specification: sep1 g k ys = sep (x : map (nest k) ys)
636 -- = oneLiner (x <g> nest k (hsep ys))
637 -- `union` x $$ nest k (vcat ys)
639 sep1 :: Bool -> RDoc -> Int -> [Doc] -> RDoc
640 sep1 g _ k ys | k `seq` False = undefined
641 sep1 g NoDoc k ys = NoDoc
642 sep1 g (p `Union` q) k ys = sep1 g p k ys
644 (aboveNest q False k (reduceDoc (vcat ys)))
646 sep1 g Empty k ys = mkNest k (sepX g ys)
647 sep1 g (Nest n p) k ys = nest_ n (sep1 g p (k - n) ys)
649 sep1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (reduceDoc (vcat ys)))
650 sep1 g (TextBeside s sl p) k ys = textBeside_ s sl (sepNB g p (k - sl) ys)
652 -- Specification: sepNB p k ys = sep1 (text "" <> p) k ys
653 -- Called when we have already found some text in the first item
654 -- We have to eat up nests
656 sepNB g (Nest _ p) k ys = sepNB g p k ys
658 sepNB g Empty k ys = oneLiner (nilBeside g (reduceDoc rest))
660 nilAboveNest False k (reduceDoc (vcat ys))
663 | otherwise = hcat ys
665 sepNB g p k ys = sep1 g p k ys
667 -- ---------------------------------------------------------------------------
676 -- fill (p1:p2:ps) = oneLiner p1 <#> nest (length p1)
677 -- (fill (oneLiner p2 : ps))
682 fill g (p:ps) = fill1 g (reduceDoc p) 0 ps
685 fill1 :: Bool -> RDoc -> Int -> [Doc] -> Doc
686 fill1 g _ k ys | k `seq` False = undefined
687 fill1 g NoDoc k ys = NoDoc
688 fill1 g (p `Union` q) k ys = fill1 g p k ys
690 (aboveNest q False k (fill g ys))
692 fill1 g Empty k ys = mkNest k (fill g ys)
693 fill1 g (Nest n p) k ys = nest_ n (fill1 g p (k - n) ys)
695 fill1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (fill g ys))
696 fill1 g (TextBeside s sl p) k ys = textBeside_ s sl (fillNB g p (k - sl) ys)
698 fillNB g _ k ys | k `seq` False = undefined
699 fillNB g (Nest _ p) k ys = fillNB g p k ys
700 fillNB g Empty k [] = Empty
701 fillNB g Empty k (y:ys) = nilBeside g (fill1 g (oneLiner (reduceDoc y)) k1 ys)
703 nilAboveNest False k (fill g (y:ys))
708 fillNB g p k ys = fill1 g p k ys
711 -- ---------------------------------------------------------------------------
712 -- Selecting the best layout
715 -> Int -- Line length
716 -> Int -- Ribbon length
718 -> RDoc -- No unions in here!
720 best OneLineMode w r p
725 get (NilAbove p) = nilAbove_ (get p)
726 get (TextBeside s sl p) = textBeside_ s sl (get p)
727 get (Nest k p) = get p -- Elide nest
728 get (p `Union` q) = first (get p) (get q)
733 get :: Int -- (Remaining) width of line
735 get w _ | w==0 && False = undefined
738 get w (NilAbove p) = nilAbove_ (get w p)
739 get w (TextBeside s sl p) = textBeside_ s sl (get1 w sl p)
740 get w (Nest k p) = nest_ k (get (w - k) p)
741 get w (p `Union` q) = nicest w r (get w p) (get w q)
743 get1 :: Int -- (Remaining) width of line
744 -> Int -- Amount of first line already eaten up
745 -> Doc -- This is an argument to TextBeside => eat Nests
746 -> Doc -- No unions in here!
748 get1 w _ _ | w==0 && False = undefined
749 get1 w sl Empty = Empty
750 get1 w sl NoDoc = NoDoc
751 get1 w sl (NilAbove p) = nilAbove_ (get (w - sl) p)
752 get1 w sl (TextBeside t tl p) = textBeside_ t tl (get1 w (sl + tl) p)
753 get1 w sl (Nest k p) = get1 w sl p
754 get1 w sl (p `Union` q) = nicest1 w r sl (get1 w sl p)
757 nicest w r p q = nicest1 w r 0 p q
758 nicest1 w r sl p q | fits ((w `minn` r) - sl) p = p
761 fits :: Int -- Space available
763 -> Bool -- True if *first line* of Doc fits in space available
765 fits n p | n < 0 = False
768 fits n (NilAbove _) = True
769 fits n (TextBeside _ sl p) = fits (n - sl) p
774 -- @first@ and @nonEmptySet@ are similar to @nicest@ and @fits@, only simpler.
775 -- @first@ returns its first argument if it is non-empty, otherwise its second.
777 first p q | nonEmptySet p = p
780 nonEmptySet NoDoc = False
781 nonEmptySet (p `Union` q) = True
782 nonEmptySet Empty = True
783 nonEmptySet (NilAbove p) = True -- NoDoc always in first line
784 nonEmptySet (TextBeside _ _ p) = nonEmptySet p
785 nonEmptySet (Nest _ p) = nonEmptySet p
787 -- @oneLiner@ returns the one-line members of the given set of @Doc@s.
789 oneLiner :: Doc -> Doc
790 oneLiner NoDoc = NoDoc
791 oneLiner Empty = Empty
792 oneLiner (NilAbove p) = NoDoc
793 oneLiner (TextBeside s sl p) = textBeside_ s sl (oneLiner p)
794 oneLiner (Nest k p) = nest_ k (oneLiner p)
795 oneLiner (p `Union` q) = oneLiner p
798 -- ---------------------------------------------------------------------------
799 -- Displaying the best layout
801 renderStyle style doc
802 = fullRender (mode style)
804 (ribbonsPerLine style)
809 render doc = showDoc doc ""
810 showDoc doc rest = fullRender PageMode 100 1.5 string_txt rest doc
812 string_txt (Chr c) s = c:s
813 string_txt (Str s1) s2 = s1 ++ s2
814 string_txt (PStr s1) s2 = s1 ++ s2
817 fullRender OneLineMode _ _ txt end doc = easy_display space_text txt end (reduceDoc doc)
818 fullRender LeftMode _ _ txt end doc = easy_display nl_text txt end (reduceDoc doc)
820 fullRender mode line_length ribbons_per_line txt end doc
821 = display mode line_length ribbon_length txt end best_doc
823 best_doc = best mode hacked_line_length ribbon_length (reduceDoc doc)
825 hacked_line_length, ribbon_length :: Int
826 ribbon_length = round (fromIntegral line_length / ribbons_per_line)
827 hacked_line_length = case mode of { ZigZagMode -> maxBound; other -> line_length }
829 display mode page_width ribbon_width txt end doc
830 = case page_width - ribbon_width of { gap_width ->
831 case gap_width `quot` 2 of { shift ->
833 lay k _ | k `seq` False = undefined
834 lay k (Nest k1 p) = lay (k + k1) p
837 lay k (NilAbove p) = nl_text `txt` lay k p
839 lay k (TextBeside s sl p)
841 ZigZagMode | k >= gap_width
843 Str (multi_ch shift '/') `txt` (
845 lay1 (k - shift) s sl p)))
849 Str (multi_ch shift '\\') `txt` (
851 lay1 (k + shift) s sl p )))
853 other -> lay1 k s sl p
855 lay1 k _ sl _ | k+sl `seq` False = undefined
856 lay1 k s sl p = Str (indent k) `txt` (s `txt` lay2 (k + sl) p)
858 lay2 k _ | k `seq` False = undefined
859 lay2 k (NilAbove p) = nl_text `txt` lay k p
860 lay2 k (TextBeside s sl p) = s `txt` (lay2 (k + sl) p)
861 lay2 k (Nest _ p) = lay2 k p
867 cant_fail = error "easy_display: NoDoc"
868 easy_display nl_text txt end doc
871 lay NoDoc no_doc = no_doc
872 lay (Union p q) no_doc = {- lay p -} (lay q cant_fail) -- Second arg can't be NoDoc
873 lay (Nest k p) no_doc = lay p no_doc
874 lay Empty no_doc = end
875 lay (NilAbove p) no_doc = nl_text `txt` lay p cant_fail -- NoDoc always on first line
876 lay (TextBeside s sl p) no_doc = s `txt` lay p no_doc
878 indent n | n >= 8 = '\t' : indent (n - 8)
879 | otherwise = spaces n
882 multi_ch n ch = ch : multi_ch (n - 1) ch
884 -- (spaces n) generates a list of n spaces
886 -- It should never be called with 'n' < 0, but that can happen for reasons I don't understand
887 -- Here's a test case:
888 -- ncat x y = nest 4 $ cat [ x, y ]
889 -- d1 = foldl1 ncat $ take 50 $ repeat $ char 'a'
890 -- d2 = parens $ sep [ d1, text "+" , d1 ]
892 -- I don't feel motivated enough to find the Real Bug, so meanwhile we just test for n<=0
893 spaces n | n <= 0 = ""
894 | otherwise = ' ' : spaces (n - 1)