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 wierd 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 $$, and anywhere in the argument list for
100 sep, hcat, hsep, vcat, fcat etc.
102 It is Really Useful in practice.
104 2. There is a paragraph-fill combinator, fsep, that's much like sep,
105 only it keeps fitting things on one line until itc can't fit any more.
107 3. Some random useful extra combinators are provided.
108 <+> puts its arguments beside each other with a space between them,
109 unless either argument is empty in which case it returns the other
112 hcat is a list version of <>
113 hsep is a list version of <+>
114 vcat is a list version of $$
116 sep (separate) is either like hsep or like vcat, depending on what fits
118 cat is behaves like sep, but it uses <> for horizontal conposition
119 fcat is 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 Mode(..), TextDetails(..),
174 empty, isEmpty, nest,
177 int, integer, float, double, rational,
178 parens, brackets, braces, quotes, doubleQuotes,
179 semi, comma, colon, space, equals,
180 lparen, rparen, lbrack, rbrack, lbrace, rbrace,
182 (<>), (<+>), hcat, hsep,
189 -- renderStyle, -- Haskell 1.3 only
200 -- ---------------------------------------------------------------------------
203 -- The primitive Doc values
206 isEmpty :: Doc -> Bool
207 text :: String -> Doc
210 semi, comma, colon, space, equals :: Doc
211 lparen, rparen, lbrack, rbrack, lbrace, rbrace :: Doc
213 parens, brackets, braces :: Doc -> Doc
214 quotes, doubleQuotes :: Doc -> Doc
217 integer :: Integer -> Doc
218 float :: Float -> Doc
219 double :: Double -> Doc
220 rational :: Rational -> Doc
223 -- Combining @Doc@ values
225 (<>) :: Doc -> Doc -> Doc -- Beside
226 hcat :: [Doc] -> Doc -- List version of <>
227 (<+>) :: Doc -> Doc -> Doc -- Beside, separated by space
228 hsep :: [Doc] -> Doc -- List version of <+>
230 ($$) :: Doc -> Doc -> Doc -- Above; if there is no
231 -- overlap it "dovetails" the two
232 vcat :: [Doc] -> Doc -- List version of $$
234 cat :: [Doc] -> Doc -- Either hcat or vcat
235 sep :: [Doc] -> Doc -- Either hsep or vcat
236 fcat :: [Doc] -> Doc -- ``Paragraph fill'' version of cat
237 fsep :: [Doc] -> Doc -- ``Paragraph fill'' version of sep
239 nest :: Int -> Doc -> Doc -- Nested
242 -- GHC-specific ones.
244 hang :: Doc -> Int -> Doc -> Doc
245 punctuate :: Doc -> [Doc] -> [Doc] -- punctuate p [d1, ... dn] = [d1 <> p, d2 <> p, ... dn-1 <> p, dn]
248 -- Displaying @Doc@ values.
250 instance Show Doc where
251 showsPrec prec doc cont = showDoc doc cont
253 render :: Doc -> String -- Uses default style
255 -> Int -- Line length
256 -> Float -- Ribbons per line
257 -> (TextDetails -> a -> a) -- What to do with text
258 -> a -- What to do at the end
262 {- When we start using 1.3
263 renderStyle :: Style -> Doc -> String
264 data Style = Style { lineLength :: Int, -- In chars
265 ribbonsPerLine :: Float, -- Ratio of ribbon length to line length
268 style :: Style -- The default style
269 style = Style { lineLength = 100, ribbonsPerLine = 2.5, mode = PageMode }
272 data Mode = PageMode -- Normal
273 | ZigZagMode -- With zig-zag cuts
274 | LeftMode -- No indentation, infinitely long lines
275 | OneLineMode -- All on one line
278 -- ---------------------------------------------------------------------------
281 -- The Doc combinators satisfy the following laws:
286 <a1> (x $$ y) $$ z = x $$ (y $$ z)
294 <b1> (x <> y) <> z = x <> (y <> z)
295 <b2> empty <> x = empty
302 <t1> text s <> text t = text (s++t)
303 <t2> text "" <> x = x, if x non-empty
308 <n2> nest k (nest k' x) = nest (k+k') x
309 <n3> nest k (x <> y) = nest k z <> nest k y
310 <n4> nest k (x $$ y) = nest k x $$ nest k y
311 <n5> nest k empty = empty
312 <n6> x <> nest k y = x <> y, if x non-empty
314 ** Note the side condition on <n6>! It is this that
315 ** makes it OK for empty to be a left unit for <>.
319 <m1> (text s <> x) $$ y = text s <> ((text "" <> x)) $$
322 <m2> (x $$ y) <> z = x $$ (y <> z)
326 Laws for list versions
327 ~~~~~~~~~~~~~~~~~~~~~~
328 <l1> sep (ps++[empty]++qs) = sep (ps ++ qs)
329 ...ditto hsep, hcat, vcat, fill...
331 <l2> nest k (sep ps) = sep (map (nest k) ps)
332 ...ditto hsep, hcat, vcat, fill...
336 <o1> oneLiner (nest k p) = nest k (oneLiner p)
337 <o2> oneLiner (x <> y) = oneLiner x <> oneLiner y
339 You might think that the following verion of <m1> would
342 <3 NO> (text s <> x) $$ y = text s <> ((empty <> x)) $$
345 But it doesn't work, for if x=empty, we would have
347 text s $$ y = text s <> (empty $$ nest (-length s) y)
348 = text s <> nest (-length s) y
351 -- ---------------------------------------------------------------------------
352 -- Simple derived definitions
366 int n = text (show n)
367 integer n = text (show n)
368 float n = text (show n)
369 double n = text (show n)
370 rational n = text (show n)
371 -- SIGBJORN wrote instead:
372 -- rational n = text (show (fromRationalX n))
374 quotes p = char '`' <> p <> char '\''
375 doubleQuotes p = char '"' <> p <> char '"'
376 parens p = char '(' <> p <> char ')'
377 brackets p = char '[' <> p <> char ']'
378 braces p = char '{' <> p <> char '}'
381 hcat = foldr (<>) empty
382 hsep = foldr (<+>) empty
383 vcat = foldr ($$) empty
385 hang d1 n d2 = sep [d1, nest n d2]
388 punctuate p (d:ds) = go d ds
391 go d (e:es) = (d <> p) : go e es
393 -- ---------------------------------------------------------------------------
396 -- A Doc represents a *set* of layouts. A Doc with
397 -- no occurrences of Union or NoDoc represents just one layout.
401 | NilAbove Doc -- text "" $$ x
402 | TextBeside TextDetails !Int Doc -- text s <> x
403 | Nest !Int Doc -- nest k x
404 | Union Doc Doc -- ul `union` ur
405 | NoDoc -- The empty set of documents
406 | Beside Doc Bool Doc -- True <=> space between
407 | Above Doc Bool Doc -- True <=> never overlap
409 type RDoc = Doc -- RDoc is a "reduced Doc", guaranteed not to have a top-level Above or Beside
412 reduceDoc :: Doc -> RDoc
413 reduceDoc (Beside p g q) = beside p g (reduceDoc q)
414 reduceDoc (Above p g q) = above p g (reduceDoc q)
418 data TextDetails = Chr Char
425 Here are the invariants:
427 * The argument of NilAbove is never Empty. Therefore
428 a NilAbove occupies at least two lines.
430 * The arugment of @TextBeside@ is never @Nest@.
433 * The layouts of the two arguments of @Union@ both flatten to the same
436 * The arguments of @Union@ are either @TextBeside@, or @NilAbove@.
438 * The right argument of a union cannot be equivalent to the empty set
439 (@NoDoc@). If the left argument of a union is equivalent to the
440 empty set (@NoDoc@), then the @NoDoc@ appears in the first line.
442 * An empty document is always represented by @Empty@. It can't be
443 hidden inside a @Nest@, or a @Union@ of two @Empty@s.
445 * The first line of every layout in the left argument of @Union@ is
446 longer than the first line of any layout in the right argument.
447 (1) ensures that the left argument has a first line. In view of
448 (3), this invariant means that the right argument must have at
452 -- Arg of a NilAbove is always an RDoc
453 nilAbove_ p = NilAbove p
455 -- Arg of a TextBeside is always an RDoc
456 textBeside_ s sl p = TextBeside s sl p
458 -- Arg of Nest is always an RDoc
461 -- Args of union are always RDocs
462 union_ p q = Union p q
465 -- Notice the difference between
466 -- * NoDoc (no documents)
467 -- * Empty (one empty document; no height and no width)
468 -- * text "" (a document containing the empty string;
469 -- one line high, but has no width)
472 -- ---------------------------------------------------------------------------
473 -- @empty@, @text@, @nest@, @union@
480 char c = textBeside_ (Chr c) 1 Empty
481 text s = case length s of {sl -> textBeside_ (Str s) sl Empty}
482 ptext s = case length s of {sl -> textBeside_ (PStr s) sl Empty}
484 nest k p = mkNest k (reduceDoc p) -- Externally callable version
486 -- mkNest checks for Nest's invariant that it doesn't have an Empty inside it
487 mkNest k _ | k `seq` False = undefined
488 mkNest k (Nest k1 p) = mkNest (k + k1) p
489 mkNest k NoDoc = NoDoc
490 mkNest k Empty = Empty
491 mkNest 0 p = p -- Worth a try!
492 mkNest k p = nest_ k p
494 -- mkUnion checks for an empty document
495 mkUnion Empty q = Empty
496 mkUnion p q = p `union_` q
498 -- ---------------------------------------------------------------------------
499 -- Vertical composition @$$@
501 p $$ q = Above p False q
502 p $+$ q = Above p True q
504 above :: Doc -> Bool -> RDoc -> RDoc
505 above (Above p g1 q1) g2 q2 = above p g1 (above q1 g2 q2)
506 above p@(Beside _ _ _) g q = aboveNest (reduceDoc p) g 0 (reduceDoc q)
507 above p g q = aboveNest p g 0 (reduceDoc q)
509 aboveNest :: RDoc -> Bool -> Int -> RDoc -> RDoc
510 -- Specfication: aboveNest p g k q = p $g$ (nest k q)
512 aboveNest _ _ k _ | k `seq` False = undefined
513 aboveNest NoDoc g k q = NoDoc
514 aboveNest (p1 `Union` p2) g k q = aboveNest p1 g k q `union_`
517 aboveNest Empty g k q = mkNest k q
518 aboveNest (Nest k1 p) g k q = nest_ k1 (aboveNest p g (k - k1) q)
519 -- p can't be Empty, so no need for mkNest
521 aboveNest (NilAbove p) g k q = nilAbove_ (aboveNest p g k q)
522 aboveNest (TextBeside s sl p) g k q = k1 `seq` textBeside_ s sl rest
526 Empty -> nilAboveNest g k1 q
527 other -> aboveNest p g k1 q
530 nilAboveNest :: Bool -> Int -> RDoc -> RDoc
531 -- Specification: text s <> nilaboveNest g k q
532 -- = text s <> (text "" $g$ nest k q)
534 nilAboveNest _ k _ | k `seq` False = undefined
535 nilAboveNest g k Empty = Empty -- Here's why the "text s <>" is in the spec!
536 nilAboveNest g k (Nest k1 q) = nilAboveNest g (k + k1) q
538 nilAboveNest g k q | (not g) && (k > 0) -- No newline if no overlap
539 = textBeside_ (Str (spaces k)) k q
540 | otherwise -- Put them really above
541 = nilAbove_ (mkNest k q)
543 -- ---------------------------------------------------------------------------
544 -- Horizontal composition @<>@
546 p <> q = Beside p False q
547 p <+> q = Beside p True q
549 beside :: Doc -> Bool -> RDoc -> RDoc
550 -- Specification: beside g p q = p <g> q
552 beside NoDoc g q = NoDoc
553 beside (p1 `Union` p2) g q = (beside p1 g q) `union_` (beside p2 g q)
555 beside (Nest k p) g q = nest_ k (beside p g q) -- p non-empty
556 beside p@(Beside p1 g1 q1) g2 q2
557 {- (A `op1` B) `op2` C == A `op1` (B `op2` C) iff op1 == op2
558 [ && (op1 == <> || op1 == <+>) ] -}
559 | g1 == g2 = beside p1 g1 (beside q1 g2 q2)
560 | otherwise = beside (reduceDoc p) g2 q2
561 beside p@(Above _ _ _) g q = beside (reduceDoc p) g q
562 beside (NilAbove p) g q = nilAbove_ (beside p g q)
563 beside (TextBeside s sl p) g q = textBeside_ s sl rest
566 Empty -> nilBeside g q
567 other -> beside p g q
570 nilBeside :: Bool -> RDoc -> RDoc
571 -- Specification: text "" <> nilBeside g p
574 nilBeside g Empty = Empty -- Hence the text "" in the spec
575 nilBeside g (Nest _ p) = nilBeside g p
576 nilBeside g p | g = textBeside_ space_text 1 p
579 -- ---------------------------------------------------------------------------
580 -- Separate, @sep@, Hughes version
582 -- Specification: sep ps = oneLiner (hsep ps)
586 sep = sepX True -- Separate with spaces
587 cat = sepX False -- Don't
590 sepX x (p:ps) = sep1 x (reduceDoc p) 0 ps
593 -- Specification: sep1 g k ys = sep (x : map (nest k) ys)
594 -- = oneLiner (x <g> nest k (hsep ys))
595 -- `union` x $$ nest k (vcat ys)
597 sep1 :: Bool -> RDoc -> Int -> [Doc] -> RDoc
598 sep1 g _ k ys | k `seq` False = undefined
599 sep1 g NoDoc k ys = NoDoc
600 sep1 g (p `Union` q) k ys = sep1 g p k ys
602 (aboveNest q False k (reduceDoc (vcat ys)))
604 sep1 g Empty k ys = mkNest k (sepX g ys)
605 sep1 g (Nest n p) k ys = nest_ n (sep1 g p (k - n) ys)
607 sep1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (reduceDoc (vcat ys)))
608 sep1 g (TextBeside s sl p) k ys = textBeside_ s sl (sepNB g p (k - sl) ys)
610 -- Specification: sepNB p k ys = sep1 (text "" <> p) k ys
611 -- Called when we have already found some text in the first item
612 -- We have to eat up nests
614 sepNB g (Nest _ p) k ys = sepNB g p k ys
616 sepNB g Empty k ys = oneLiner (nilBeside g (reduceDoc rest))
618 nilAboveNest False k (reduceDoc (vcat ys))
621 | otherwise = hcat ys
623 sepNB g p k ys = sep1 g p k ys
625 -- ---------------------------------------------------------------------------
634 -- fill (p1:p2:ps) = oneLiner p1 <#> nest (length p1)
635 -- (fill (oneLiner p2 : ps))
640 fill g (p:ps) = fill1 g (reduceDoc p) 0 ps
643 fill1 :: Bool -> RDoc -> Int -> [Doc] -> Doc
644 fill1 g _ k ys | k `seq` False = undefined
645 fill1 g NoDoc k ys = NoDoc
646 fill1 g (p `Union` q) k ys = fill1 g p k ys
648 (aboveNest q False k (fill g ys))
650 fill1 g Empty k ys = mkNest k (fill g ys)
651 fill1 g (Nest n p) k ys = nest_ n (fill1 g p (k - n) ys)
653 fill1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (fill g ys))
654 fill1 g (TextBeside s sl p) k ys = textBeside_ s sl (fillNB g p (k - sl) ys)
656 fillNB g _ k ys | k `seq` False = undefined
657 fillNB g (Nest _ p) k ys = fillNB g p k ys
658 fillNB g Empty k [] = Empty
659 fillNB g Empty k (y:ys) = nilBeside g (fill1 g (oneLiner (reduceDoc y)) k1 ys)
661 nilAboveNest False k (fill g (y:ys))
666 fillNB g p k ys = fill1 g p k ys
669 -- ---------------------------------------------------------------------------
670 -- Selecting the best layout
673 -> Int -- Line length
674 -> Int -- Ribbon length
676 -> RDoc -- No unions in here!
678 best OneLineMode w r p
683 get (NilAbove p) = nilAbove_ (get p)
684 get (TextBeside s sl p) = textBeside_ s sl (get p)
685 get (Nest k p) = get p -- Elide nest
686 get (p `Union` q) = first (get p) (get q)
691 get :: Int -- (Remaining) width of line
693 get w _ | w==0 && False = undefined
696 get w (NilAbove p) = nilAbove_ (get w p)
697 get w (TextBeside s sl p) = textBeside_ s sl (get1 w sl p)
698 get w (Nest k p) = nest_ k (get (w - k) p)
699 get w (p `Union` q) = nicest w r (get w p) (get w q)
701 get1 :: Int -- (Remaining) width of line
702 -> Int -- Amount of first line already eaten up
703 -> Doc -- This is an argument to TextBeside => eat Nests
704 -> Doc -- No unions in here!
706 get1 w _ _ | w==0 && False = undefined
707 get1 w sl Empty = Empty
708 get1 w sl NoDoc = NoDoc
709 get1 w sl (NilAbove p) = nilAbove_ (get (w - sl) p)
710 get1 w sl (TextBeside t tl p) = textBeside_ t tl (get1 w (sl + tl) p)
711 get1 w sl (Nest k p) = get1 w sl p
712 get1 w sl (p `Union` q) = nicest1 w r sl (get1 w sl p)
715 nicest w r p q = nicest1 w r 0 p q
716 nicest1 w r sl p q | fits ((w `minn` r) - sl) p = p
719 fits :: Int -- Space available
721 -> Bool -- True if *first line* of Doc fits in space available
723 fits n p | n < 0 = False
726 fits n (NilAbove _) = True
727 fits n (TextBeside _ sl p) = fits (n - sl) p
732 -- @first@ and @nonEmptySet@ are similar to @nicest@ and @fits@, only simpler.
733 -- @first@ returns its first argument if it is non-empty, otherwise its second.
735 first p q | nonEmptySet p = p
738 nonEmptySet NoDoc = False
739 nonEmptySet (p `Union` q) = True
740 nonEmptySet Empty = True
741 nonEmptySet (NilAbove p) = True -- NoDoc always in first line
742 nonEmptySet (TextBeside _ _ p) = nonEmptySet p
743 nonEmptySet (Nest _ p) = nonEmptySet p
745 -- @oneLiner@ returns the one-line members of the given set of @Doc@s.
747 oneLiner :: Doc -> Doc
748 oneLiner NoDoc = NoDoc
749 oneLiner Empty = Empty
750 oneLiner (NilAbove p) = NoDoc
751 oneLiner (TextBeside s sl p) = textBeside_ s sl (oneLiner p)
752 oneLiner (Nest k p) = nest_ k (oneLiner p)
753 oneLiner (p `Union` q) = oneLiner p
756 -- ---------------------------------------------------------------------------
757 -- Displaying the best layout
760 renderStyle Style{mode, lineLength, ribbonsPerLine} doc
761 = fullRender mode lineLength ribbonsPerLine doc ""
764 render doc = showDoc doc ""
765 showDoc doc rest = fullRender PageMode 100 1.5 string_txt rest doc
767 string_txt (Chr c) s = c:s
768 string_txt (Str s1) s2 = s1 ++ s2
769 string_txt (PStr s1) s2 = s1 ++ s2
772 fullRender OneLineMode _ _ txt end doc = easy_display space_text txt end (reduceDoc doc)
773 fullRender LeftMode _ _ txt end doc = easy_display nl_text txt end (reduceDoc doc)
775 fullRender mode line_length ribbons_per_line txt end doc
776 = display mode line_length ribbon_length txt end best_doc
778 best_doc = best mode hacked_line_length ribbon_length (reduceDoc doc)
780 hacked_line_length, ribbon_length :: Int
781 ribbon_length = round (fromIntegral line_length / ribbons_per_line)
782 hacked_line_length = case mode of { ZigZagMode -> maxBound; other -> line_length }
784 display mode page_width ribbon_width txt end doc
785 = case page_width - ribbon_width of { gap_width ->
786 case gap_width `quot` 2 of { shift ->
788 lay k _ | k `seq` False = undefined
789 lay k (Nest k1 p) = lay (k + k1) p
792 lay k (NilAbove p) = nl_text `txt` lay k p
794 lay k (TextBeside s sl p)
796 ZigZagMode | k >= gap_width
798 Str (multi_ch shift '/') `txt` (
800 lay1 (k - shift) s sl p)))
804 Str (multi_ch shift '\\') `txt` (
806 lay1 (k + shift) s sl p )))
808 other -> lay1 k s sl p
810 lay1 k _ sl _ | k+sl `seq` False = undefined
811 lay1 k s sl p = Str (indent k) `txt` (s `txt` lay2 (k + sl) p)
813 lay2 k _ | k `seq` False = undefined
814 lay2 k (NilAbove p) = nl_text `txt` lay k p
815 lay2 k (TextBeside s sl p) = s `txt` (lay2 (k + sl) p)
816 lay2 k (Nest _ p) = lay2 k p
822 cant_fail = error "easy_display: NoDoc"
823 easy_display nl_text txt end doc
826 lay NoDoc no_doc = no_doc
827 lay (Union p q) no_doc = {- lay p -} (lay q cant_fail) -- Second arg can't be NoDoc
828 lay (Nest k p) no_doc = lay p no_doc
829 lay Empty no_doc = end
830 lay (NilAbove p) no_doc = nl_text `txt` lay p cant_fail -- NoDoc always on first line
831 lay (TextBeside s sl p) no_doc = s `txt` lay p no_doc
833 indent n | n >= 8 = '\t' : indent (n - 8)
834 | otherwise = spaces n
837 multi_ch n ch = ch : multi_ch (n - 1) ch
840 spaces n = ' ' : spaces (n - 1)