1 *********************************************************************************
3 * John Hughes's and Simon Peyton Jones's Pretty Printer Combinators *
5 * based on "The Design of a Pretty-printing Library" *
6 * in Advanced Functional Programming, *
7 * Johan Jeuring and Erik Meijer (eds), LNCS 925 *
8 * http://www.cs.chalmers.se/~rjmh/Papers/pretty.ps *
10 * Heavily modified by Simon Peyton Jones, Dec 96 *
12 *********************************************************************************
14 Version 3.0 28 May 1997
15 * Cured massive performance bug. If you write
17 foldl <> empty (map (text.show) [1..10000])
19 you get quadratic behaviour with V2.0. Why? For just the same reason as you get
20 quadratic behaviour with left-associated (++) chains.
22 This is really bad news. One thing a pretty-printer abstraction should
23 certainly guarantee is insensivity to associativity. It matters: suddenly
24 GHC's compilation times went up by a factor of 100 when I switched to the
27 I fixed it with a bit of a hack (because I wanted to get GHC back on the
28 road). I added two new constructors to the Doc type, Above and Beside:
33 Then, where I need to get to a "TextBeside" or "NilAbove" form I "force"
34 the Doc to squeeze out these suspended calls to Beside and Above; but in so
35 doing I re-associate. It's quite simple, but I'm not satisfied that I've done
36 the best possible job. I'll send you the code if you are interested.
40 int, integer, float, double, rational,
41 lparen, rparen, lbrack, rbrack, lbrace, rbrace,
43 * fullRender's type signature has changed. Rather than producing a string it
44 now takes an extra couple of arguments that tells it how to glue fragments
49 -> Float -- Ribbons per line
50 -> (TextDetails -> a -> a) -- What to do with text
51 -> a -- What to do at the end
55 The "fragments" are encapsulated in the TextDetails data type:
56 data TextDetails = Chr Char
60 The Chr and Str constructors are obvious enough. The PStr constructor has a packed
61 string (FAST_STRING) inside it. It's generated by using the new "ptext" export.
63 An advantage of this new setup is that you can get the renderer to do output
64 directly (by passing in a function of type (TextDetails -> IO () -> IO ()),
65 rather than producing a string that you then print.
68 Version 2.0 24 April 1997
69 * Made empty into a left unit for <> as well as a right unit;
70 it is also now true that
72 which wasn't true before.
74 * Fixed an obscure bug in sep that occassionally gave very wierd behaviour
78 * Corrected and tidied up the laws and invariants
80 ======================================================================
81 Relative to John's original paper, there are the following new features:
83 1. There's an empty document, "empty". It's a left and right unit for
84 both <> and $$, and anywhere in the argument list for
85 sep, hcat, hsep, vcat, fcat etc.
87 It is Really Useful in practice.
89 2. There is a paragraph-fill combinator, fsep, that's much like sep,
90 only it keeps fitting things on one line until itc can't fit any more.
92 3. Some random useful extra combinators are provided.
93 <+> puts its arguments beside each other with a space between them,
94 unless either argument is empty in which case it returns the other
97 hcat is a list version of <>
98 hsep is a list version of <+>
99 vcat is a list version of $$
101 sep (separate) is either like hsep or like vcat, depending on what fits
103 cat is behaves like sep, but it uses <> for horizontal conposition
104 fcat is behaves like fsep, but it uses <> for horizontal conposition
106 These new ones do the obvious things:
107 char, semi, comma, colon, space,
108 parens, brackets, braces,
111 4. The "above" combinator, $$, now overlaps its two arguments if the
112 last line of the top argument stops before the first line of the second begins.
113 For example: text "hi" $$ nest 5 "there"
120 There are two places this is really useful
122 a) When making labelled blocks, like this:
123 Left -> code for left
124 Right -> code for right
126 code for longlonglonglabel
127 The block is on the same line as the label if the label is
128 short, but on the next line otherwise.
130 b) When laying out lists like this:
135 which some people like. But if the list fits on one line
136 you want [first, second, third]. You can't do this with
137 John's original combinators, but it's quite easy with the
140 The combinator $+$ gives the original "never-overlap" behaviour.
142 5. Several different renderers are provided:
144 * one that uses cut-marks to avoid deeply-nested documents
145 simply piling up in the right-hand margin
146 * one that ignores indentation (fewer chars output; good for machines)
147 * one that ignores indentation and newlines (ditto, only more so)
149 6. Numerous implementation tidy-ups
150 Use of unboxed data types to speed up the implementation
157 Mode(..), TextDetails(..),
159 empty, isEmpty, nest,
162 int, integer, float, double, rational,
163 parens, brackets, braces, quotes, doubleQuotes,
164 semi, comma, colon, space, equals,
165 lparen, rparen, lbrack, rbrack, lbrace, rbrace,
167 (<>), (<+>), hcat, hsep,
174 -- renderStyle, -- Haskell 1.3 only
178 -- Don't import Util( assertPanic ) because it makes a loop in the module structure
187 *********************************************************
189 \subsection{CPP magic so that we can compile with both GHC and Hugs}
191 *********************************************************
193 The library uses unboxed types to get a bit more speed, but these CPP macros
194 allow you to use either GHC or Hugs. To get GHC, just set the CPP variable
198 *********************************************************
200 \subsection{The interface}
202 *********************************************************
204 The primitive @Doc@ values
208 isEmpty :: Doc -> Bool
209 text :: String -> Doc
212 semi, comma, colon, space, equals :: Doc
213 lparen, rparen, lbrack, rbrack, lbrace, rbrace :: Doc
215 parens, brackets, braces :: Doc -> Doc
216 quotes, doubleQuotes :: Doc -> Doc
219 integer :: Integer -> Doc
220 float :: Float -> Doc
221 double :: Double -> Doc
222 rational :: Rational -> Doc
225 Combining @Doc@ values
228 (<>) :: Doc -> Doc -> Doc -- Beside
229 hcat :: [Doc] -> Doc -- List version of <>
230 (<+>) :: Doc -> Doc -> Doc -- Beside, separated by space
231 hsep :: [Doc] -> Doc -- List version of <+>
233 ($$) :: Doc -> Doc -> Doc -- Above; if there is no
234 -- overlap it "dovetails" the two
235 vcat :: [Doc] -> Doc -- List version of $$
237 cat :: [Doc] -> Doc -- Either hcat or vcat
238 sep :: [Doc] -> Doc -- Either hsep or vcat
239 fcat :: [Doc] -> Doc -- ``Paragraph fill'' version of cat
240 fsep :: [Doc] -> Doc -- ``Paragraph fill'' version of sep
242 nest :: Int -> Doc -> Doc -- Nested
248 hang :: Doc -> Int -> Doc -> Doc
249 punctuate :: Doc -> [Doc] -> [Doc] -- punctuate p [d1, ... dn] = [d1 <> p, d2 <> p, ... dn-1 <> p, dn]
252 Displaying @Doc@ values.
255 instance Show Doc where
256 showsPrec prec doc cont = showDoc doc cont
258 render :: Doc -> String -- Uses default style
260 -> Int -- Line length
261 -> Float -- Ribbons per line
262 -> (TextDetails -> a -> a) -- What to do with text
263 -> a -- What to do at the end
267 {- When we start using 1.3
268 renderStyle :: Style -> Doc -> String
269 data Style = Style { lineLength :: Int, -- In chars
270 ribbonsPerLine :: Float, -- Ratio of ribbon length to line length
273 style :: Style -- The default style
274 style = Style { lineLength = 100, ribbonsPerLine = 2.5, mode = PageMode }
277 data Mode = PageMode -- Normal
278 | ZigZagMode -- With zig-zag cuts
279 | LeftMode -- No indentation, infinitely long lines
280 | OneLineMode -- All on one line
285 *********************************************************
287 \subsection{The @Doc@ calculus}
289 *********************************************************
291 The @Doc@ combinators satisfy the following laws:
295 <a1> (x $$ y) $$ z = x $$ (y $$ z)
303 <b1> (x <> y) <> z = x <> (y <> z)
304 <b2> empty <> x = empty
311 <t1> text s <> text t = text (s++t)
312 <t2> text "" <> x = x, if x non-empty
317 <n2> nest k (nest k' x) = nest (k+k') x
318 <n3> nest k (x <> y) = nest k z <> nest k y
319 <n4> nest k (x $$ y) = nest k x $$ nest k y
320 <n5> nest k empty = empty
321 <n6> x <> nest k y = x <> y, if x non-empty
323 ** Note the side condition on <n6>! It is this that
324 ** makes it OK for empty to be a left unit for <>.
328 <m1> (text s <> x) $$ y = text s <> ((text "" <> x)) $$
331 <m2> (x $$ y) <> z = x $$ (y <> z)
335 Laws for list versions
336 ~~~~~~~~~~~~~~~~~~~~~~
337 <l1> sep (ps++[empty]++qs) = sep (ps ++ qs)
338 ...ditto hsep, hcat, vcat, fill...
340 <l2> nest k (sep ps) = sep (map (nest k) ps)
341 ...ditto hsep, hcat, vcat, fill...
345 <o1> oneLiner (nest k p) = nest k (oneLiner p)
346 <o2> oneLiner (x <> y) = oneLiner x <> oneLiner y
350 You might think that the following verion of <m1> would
353 <3 NO> (text s <> x) $$ y = text s <> ((empty <> x)) $$
356 But it doesn't work, for if x=empty, we would have
358 text s $$ y = text s <> (empty $$ nest (-length s) y)
359 = text s <> nest (-length s) y
364 *********************************************************
366 \subsection{Simple derived definitions}
368 *********************************************************
383 int n = text (show n)
384 integer n = text (show n)
385 float n = text (show n)
386 double n = text (show n)
387 rational n = text (show n)
388 -- SIGBJORN wrote instead:
389 -- rational n = text (show (fromRationalX n))
391 quotes p = char '`' <> p <> char '\''
392 doubleQuotes p = char '"' <> p <> char '"'
393 parens p = char '(' <> p <> char ')'
394 brackets p = char '[' <> p <> char ']'
395 braces p = char '{' <> p <> char '}'
398 hcat = foldr (<>) empty
399 hsep = foldr (<+>) empty
400 vcat = foldr ($$) empty
402 hang d1 n d2 = sep [d1, nest n d2]
405 punctuate p (d:ds) = go d ds
408 go d (e:es) = (d <> p) : go e es
412 *********************************************************
414 \subsection{The @Doc@ data type}
416 *********************************************************
418 A @Doc@ represents a {\em set} of layouts. A @Doc@ with
419 no occurrences of @Union@ or @NoDoc@ represents just one layout.
423 | NilAbove Doc -- text "" $$ x
424 | TextBeside TextDetails Int Doc -- text s <> x
425 | Nest Int Doc -- nest k x
426 | Union Doc Doc -- ul `union` ur
427 | NoDoc -- The empty set of documents
428 | Beside Doc Bool Doc -- True <=> space between
429 | Above Doc Bool Doc -- True <=> never overlap
431 type RDoc = Doc -- RDoc is a "reduced Doc", guaranteed not to have a top-level Above or Beside
434 reduceDoc :: Doc -> RDoc
435 reduceDoc (Beside p g q) = beside p g (reduceDoc q)
436 reduceDoc (Above p g q) = above p g (reduceDoc q)
440 data TextDetails = Chr Char
447 Here are the invariants:
450 The argument of @NilAbove@ is never @Empty@. Therefore
451 a @NilAbove@ occupies at least two lines.
454 The arugment of @TextBeside@ is never @Nest@.
457 The layouts of the two arguments of @Union@ both flatten to the same string.
460 The arguments of @Union@ are either @TextBeside@, or @NilAbove@.
463 The right argument of a union cannot be equivalent to the empty set (@NoDoc@).
464 If the left argument of a union is equivalent to the empty set (@NoDoc@),
465 then the @NoDoc@ appears in the first line.
468 An empty document is always represented by @Empty@.
469 It can't be hidden inside a @Nest@, or a @Union@ of two @Empty@s.
472 The first line of every layout in the left argument of @Union@
473 is longer than the first line of any layout in the right argument.
474 (1) ensures that the left argument has a first line. In view of (3),
475 this invariant means that the right argument must have at least two
480 -- Arg of a NilAbove is always an RDoc
481 nilAbove_ p = NilAbove p
483 -- Arg of a TextBeside is always an RDoc
484 textBeside_ s sl p = TextBeside s sl p
486 -- Arg of Nest is always an RDoc
489 -- Args of union are always RDocs
490 union_ p q = Union p q
495 Notice the difference between
496 * NoDoc (no documents)
497 * Empty (one empty document; no height and no width)
498 * text "" (a document containing the empty string;
499 one line high, but has no width)
503 *********************************************************
505 \subsection{@empty@, @text@, @nest@, @union@}
507 *********************************************************
515 char c = textBeside_ (Chr c) 1 Empty
516 text s = case length s of {sl -> textBeside_ (Str s) sl Empty}
517 ptext s = case length s of {sl -> textBeside_ (PStr s) sl Empty}
519 nest k p = mkNest k (reduceDoc p) -- Externally callable version
521 -- mkNest checks for Nest's invariant that it doesn't have an Empty inside it
522 mkNest k (Nest k1 p) = mkNest (k + k1) p
523 mkNest k NoDoc = NoDoc
524 mkNest k Empty = Empty
525 mkNest 0 p = p -- Worth a try!
526 mkNest k p = nest_ k p
528 -- mkUnion checks for an empty document
529 mkUnion Empty q = Empty
530 mkUnion p q = p `union_` q
533 *********************************************************
535 \subsection{Vertical composition @$$@}
537 *********************************************************
541 p $$ q = Above p False q
542 p $+$ q = Above p True q
544 above :: Doc -> Bool -> RDoc -> RDoc
545 above (Above p g1 q1) g2 q2 = above p g1 (above q1 g2 q2)
546 above p@(Beside _ _ _) g q = aboveNest (reduceDoc p) g 0 (reduceDoc q)
547 above p g q = aboveNest p g 0 (reduceDoc q)
549 aboveNest :: RDoc -> Bool -> Int -> RDoc -> RDoc
550 -- Specfication: aboveNest p g k q = p $g$ (nest k q)
552 aboveNest NoDoc g k q = NoDoc
553 aboveNest (p1 `Union` p2) g k q = aboveNest p1 g k q `union_`
556 aboveNest Empty g k q = mkNest k q
557 aboveNest (Nest k1 p) g k q = nest_ k1 (aboveNest p g (k - k1) q)
558 -- p can't be Empty, so no need for mkNest
560 aboveNest (NilAbove p) g k q = nilAbove_ (aboveNest p g k q)
561 aboveNest (TextBeside s sl p) g k q = textBeside_ s sl rest
565 Empty -> nilAboveNest g k1 q
566 other -> aboveNest p g k1 q
570 nilAboveNest :: Bool -> Int -> RDoc -> RDoc
571 -- Specification: text s <> nilaboveNest g k q
572 -- = text s <> (text "" $g$ nest k q)
574 nilAboveNest g k Empty = Empty -- Here's why the "text s <>" is in the spec!
575 nilAboveNest g k (Nest k1 q) = nilAboveNest g (k + k1) q
577 nilAboveNest g k q | (not g) && (k > 0) -- No newline if no overlap
578 = textBeside_ (Str (spaces k)) k q
579 | otherwise -- Put them really above
580 = nilAbove_ (mkNest k q)
584 *********************************************************
586 \subsection{Horizontal composition @<>@}
588 *********************************************************
591 p <> q = Beside p False q
592 p <+> q = Beside p True q
594 beside :: Doc -> Bool -> RDoc -> RDoc
595 -- Specification: beside g p q = p <g> q
597 beside NoDoc g q = NoDoc
598 beside (p1 `Union` p2) g q = (beside p1 g q) `union_` (beside p2 g q)
600 beside (Nest k p) g q = nest_ k (beside p g q) -- p non-empty
601 beside p@(Beside p1 g1 q1) g2 q2
602 {- (A `op1` B) `op2` C == A `op1` (B `op2` C) iff op1 == op2
603 [ && (op1 == <> || op1 == <+>) ] -}
604 | g1 == g2 = beside p1 g1 (beside q1 g2 q2)
605 | otherwise = beside (reduceDoc p) g2 q2
606 beside p@(Above _ _ _) g q = beside (reduceDoc p) g q
607 beside (NilAbove p) g q = nilAbove_ (beside p g q)
608 beside (TextBeside s sl p) g q = textBeside_ s sl rest
611 Empty -> nilBeside g q
612 other -> beside p g q
616 nilBeside :: Bool -> RDoc -> RDoc
617 -- Specification: text "" <> nilBeside g p
620 nilBeside g Empty = Empty -- Hence the text "" in the spec
621 nilBeside g (Nest _ p) = nilBeside g p
622 nilBeside g p | g = textBeside_ space_text 1 p
626 *********************************************************
628 \subsection{Separate, @sep@, Hughes version}
630 *********************************************************
633 -- Specification: sep ps = oneLiner (hsep ps)
637 sep = sepX True -- Separate with spaces
638 cat = sepX False -- Don't
641 sepX x (p:ps) = sep1 x (reduceDoc p) 0 ps
644 -- Specification: sep1 g k ys = sep (x : map (nest k) ys)
645 -- = oneLiner (x <g> nest k (hsep ys))
646 -- `union` x $$ nest k (vcat ys)
648 sep1 :: Bool -> RDoc -> Int -> [Doc] -> RDoc
649 sep1 g _ k ys | k == 0 && False = undefined
650 sep1 g NoDoc k ys = NoDoc
651 sep1 g (p `Union` q) k ys = sep1 g p k ys
653 (aboveNest q False k (reduceDoc (vcat ys)))
655 sep1 g Empty k ys = mkNest k (sepX g ys)
656 sep1 g (Nest n p) k ys = nest_ n (sep1 g p (k - n) ys)
658 sep1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (reduceDoc (vcat ys)))
659 sep1 g (TextBeside s sl p) k ys = textBeside_ s sl (sepNB g p (k - sl) ys)
661 -- Specification: sepNB p k ys = sep1 (text "" <> p) k ys
662 -- Called when we have already found some text in the first item
663 -- We have to eat up nests
665 sepNB g (Nest _ p) k ys = sepNB g p k ys
667 sepNB g Empty k ys = oneLiner (nilBeside g (reduceDoc rest))
669 nilAboveNest False k (reduceDoc (vcat ys))
672 | otherwise = hcat ys
674 sepNB g p k ys = sep1 g p k ys
677 *********************************************************
681 *********************************************************
690 -- fill (p1:p2:ps) = oneLiner p1 <#> nest (length p1)
691 -- (fill (oneLiner p2 : ps))
696 fill g (p:ps) = fill1 g (reduceDoc p) 0 ps
699 fill1 :: Bool -> RDoc -> Int -> [Doc] -> Doc
700 fill1 g _ k ys | k == 0 && False = undefined
701 fill1 g NoDoc k ys = NoDoc
702 fill1 g (p `Union` q) k ys = fill1 g p k ys
704 (aboveNest q False k (fill g ys))
706 fill1 g Empty k ys = mkNest k (fill g ys)
707 fill1 g (Nest n p) k ys = nest_ n (fill1 g p (k - n) ys)
709 fill1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (fill g ys))
710 fill1 g (TextBeside s sl p) k ys = textBeside_ s sl (fillNB g p (k - sl) ys)
712 fillNB g _ k ys | k == 0 && False = undefined
713 fillNB g (Nest _ p) k ys = fillNB g p k ys
714 fillNB g Empty k [] = Empty
715 fillNB g Empty k (y:ys) = nilBeside g (fill1 g (oneLiner (reduceDoc y)) k1 ys)
717 nilAboveNest False k (fill g (y:ys))
722 fillNB g p k ys = fill1 g p k ys
726 *********************************************************
728 \subsection{Selecting the best layout}
730 *********************************************************
734 -> Int -- Line length
735 -> Int -- Ribbon length
737 -> RDoc -- No unions in here!
739 best OneLineMode w r p
744 get (NilAbove p) = nilAbove_ (get p)
745 get (TextBeside s sl p) = textBeside_ s sl (get p)
746 get (Nest k p) = get p -- Elide nest
747 get (p `Union` q) = first (get p) (get q)
752 get :: Int -- (Remaining) width of line
754 get w _ | w==0 && False = undefined
757 get w (NilAbove p) = nilAbove_ (get w p)
758 get w (TextBeside s sl p) = textBeside_ s sl (get1 w sl p)
759 get w (Nest k p) = nest_ k (get (w - k) p)
760 get w (p `Union` q) = nicest w r (get w p) (get w q)
762 get1 :: Int -- (Remaining) width of line
763 -> Int -- Amount of first line already eaten up
764 -> Doc -- This is an argument to TextBeside => eat Nests
765 -> Doc -- No unions in here!
767 get1 w _ _ | w==0 && False = undefined
768 get1 w sl Empty = Empty
769 get1 w sl NoDoc = NoDoc
770 get1 w sl (NilAbove p) = nilAbove_ (get (w - sl) p)
771 get1 w sl (TextBeside t tl p) = textBeside_ t tl (get1 w (sl + tl) p)
772 get1 w sl (Nest k p) = get1 w sl p
773 get1 w sl (p `Union` q) = nicest1 w r sl (get1 w sl p)
776 nicest w r p q = nicest1 w r 0 p q
777 nicest1 w r sl p q | fits ((w `minn` r) - sl) p = p
780 fits :: Int -- Space available
782 -> Bool -- True if *first line* of Doc fits in space available
784 fits n p | n < 0 = False
787 fits n (NilAbove _) = True
788 fits n (TextBeside _ sl p) = (fits $! (n - sl)) p
794 @first@ and @nonEmptySet@ are similar to @nicest@ and @fits@, only simpler.
795 @first@ returns its first argument if it is non-empty, otherwise its second.
798 first p q | nonEmptySet p = p
801 nonEmptySet NoDoc = False
802 nonEmptySet (p `Union` q) = True
803 nonEmptySet Empty = True
804 nonEmptySet (NilAbove p) = True -- NoDoc always in first line
805 nonEmptySet (TextBeside _ _ p) = nonEmptySet p
806 nonEmptySet (Nest _ p) = nonEmptySet p
809 @oneLiner@ returns the one-line members of the given set of @Doc@s.
812 oneLiner :: Doc -> Doc
813 oneLiner NoDoc = NoDoc
814 oneLiner Empty = Empty
815 oneLiner (NilAbove p) = NoDoc
816 oneLiner (TextBeside s sl p) = textBeside_ s sl (oneLiner p)
817 oneLiner (Nest k p) = nest_ k (oneLiner p)
818 oneLiner (p `Union` q) = oneLiner p
823 *********************************************************
825 \subsection{Displaying the best layout}
827 *********************************************************
832 renderStyle Style{mode, lineLength, ribbonsPerLine} doc
833 = fullRender mode lineLength ribbonsPerLine doc ""
836 render doc = showDoc doc ""
837 showDoc doc rest = fullRender PageMode 100 1.5 string_txt rest doc
839 string_txt (Chr c) s = c:s
840 string_txt (Str s1) s2 = s1 ++ s2
841 string_txt (PStr s1) s2 = s1 ++ s2
846 fullRender OneLineMode _ _ txt end doc = easy_display space_text txt end (reduceDoc doc)
847 fullRender LeftMode _ _ txt end doc = easy_display nl_text txt end (reduceDoc doc)
849 fullRender mode line_length ribbons_per_line txt end doc
850 = display mode line_length ribbon_length txt end best_doc
852 best_doc = best mode hacked_line_length ribbon_length (reduceDoc doc)
854 hacked_line_length, ribbon_length :: Int
855 ribbon_length = round (fromIntegral line_length / ribbons_per_line)
856 hacked_line_length = case mode of { ZigZagMode -> maxBound; other -> line_length }
858 display mode page_width ribbon_width txt end doc
859 = case page_width - ribbon_width of { gap_width ->
860 case gap_width `quot` 2 of { shift ->
862 lay k (Nest k1 p) = lay (k + k1) p
865 lay k (NilAbove p) = nl_text `txt` lay k p
867 lay k (TextBeside s sl p)
869 ZigZagMode | k >= gap_width
871 Str (multi_ch shift '/') `txt` (
873 lay1 (k - shift) s sl p)))
877 Str (multi_ch shift '\\') `txt` (
879 lay1 (k + shift) s sl p )))
881 other -> lay1 k s sl p
883 lay1 k s sl p = Str (indent k) `txt` (s `txt` lay2 (k + sl) p)
885 lay2 k (NilAbove p) = nl_text `txt` lay k p
886 lay2 k (TextBeside s sl p) = s `txt` (lay2 (k + sl) p)
887 lay2 k (Nest _ p) = lay2 k p
893 cant_fail = error "easy_display: NoDoc"
894 easy_display nl_text txt end doc
897 lay NoDoc no_doc = no_doc
898 lay (Union p q) no_doc = {- lay p -} (lay q cant_fail) -- Second arg can't be NoDoc
899 lay (Nest k p) no_doc = lay p no_doc
900 lay Empty no_doc = end
901 lay (NilAbove p) no_doc = nl_text `txt` lay p cant_fail -- NoDoc always on first line
902 lay (TextBeside s sl p) no_doc = s `txt` lay p no_doc
904 indent n | n >= 8 = '\t' : indent (n - 8)
905 | otherwise = spaces n
908 multi_ch n ch = ch : multi_ch (n - 1) ch
911 spaces n = ' ' : spaces (n - 1)