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
424 -- Here are the invariants:
426 -- * The argument of NilAbove is never Empty. Therefore
427 -- a NilAbove occupies at least two lines.
429 -- * The arugment of @TextBeside@ is never @Nest@.
432 -- * The layouts of the two arguments of @Union@ both flatten to the same
435 -- * The arguments of @Union@ are either @TextBeside@, or @NilAbove@.
437 -- * The right argument of a union cannot be equivalent to the empty set
438 -- (@NoDoc@). If the left argument of a union is equivalent to the
439 -- empty set (@NoDoc@), then the @NoDoc@ appears in the first line.
441 -- * An empty document is always represented by @Empty@. It can't be
442 -- hidden inside a @Nest@, or a @Union@ of two @Empty@s.
444 -- * The first line of every layout in the left argument of @Union@ is
445 -- longer than the first line of any layout in the right argument.
446 -- (1) ensures that the left argument has a first line. In view of
447 -- (3), this invariant means that the right argument must have at
451 -- Arg of a NilAbove is always an RDoc
452 nilAbove_ p = NilAbove p
454 -- Arg of a TextBeside is always an RDoc
455 textBeside_ s sl p = TextBeside s sl p
457 -- Arg of Nest is always an RDoc
460 -- Args of union are always RDocs
461 union_ p q = Union p q
464 -- Notice the difference between
465 -- * NoDoc (no documents)
466 -- * Empty (one empty document; no height and no width)
467 -- * text "" (a document containing the empty string;
468 -- one line high, but has no width)
471 -- ---------------------------------------------------------------------------
472 -- @empty@, @text@, @nest@, @union@
479 char c = textBeside_ (Chr c) 1 Empty
480 text s = case length s of {sl -> textBeside_ (Str s) sl Empty}
481 ptext s = case length s of {sl -> textBeside_ (PStr s) sl Empty}
483 nest k p = mkNest k (reduceDoc p) -- Externally callable version
485 -- mkNest checks for Nest's invariant that it doesn't have an Empty inside it
486 mkNest k _ | k `seq` False = undefined
487 mkNest k (Nest k1 p) = mkNest (k + k1) p
488 mkNest k NoDoc = NoDoc
489 mkNest k Empty = Empty
490 mkNest 0 p = p -- Worth a try!
491 mkNest k p = nest_ k p
493 -- mkUnion checks for an empty document
494 mkUnion Empty q = Empty
495 mkUnion p q = p `union_` q
497 -- ---------------------------------------------------------------------------
498 -- Vertical composition @$$@
500 p $$ q = Above p False q
501 p $+$ q = Above p True q
503 above :: Doc -> Bool -> RDoc -> RDoc
504 above (Above p g1 q1) g2 q2 = above p g1 (above q1 g2 q2)
505 above p@(Beside _ _ _) g q = aboveNest (reduceDoc p) g 0 (reduceDoc q)
506 above p g q = aboveNest p g 0 (reduceDoc q)
508 aboveNest :: RDoc -> Bool -> Int -> RDoc -> RDoc
509 -- Specfication: aboveNest p g k q = p $g$ (nest k q)
511 aboveNest _ _ k _ | k `seq` False = undefined
512 aboveNest NoDoc g k q = NoDoc
513 aboveNest (p1 `Union` p2) g k q = aboveNest p1 g k q `union_`
516 aboveNest Empty g k q = mkNest k q
517 aboveNest (Nest k1 p) g k q = nest_ k1 (aboveNest p g (k - k1) q)
518 -- p can't be Empty, so no need for mkNest
520 aboveNest (NilAbove p) g k q = nilAbove_ (aboveNest p g k q)
521 aboveNest (TextBeside s sl p) g k q = k1 `seq` textBeside_ s sl rest
525 Empty -> nilAboveNest g k1 q
526 other -> aboveNest p g k1 q
529 nilAboveNest :: Bool -> Int -> RDoc -> RDoc
530 -- Specification: text s <> nilaboveNest g k q
531 -- = text s <> (text "" $g$ nest k q)
533 nilAboveNest _ k _ | k `seq` False = undefined
534 nilAboveNest g k Empty = Empty -- Here's why the "text s <>" is in the spec!
535 nilAboveNest g k (Nest k1 q) = nilAboveNest g (k + k1) q
537 nilAboveNest g k q | (not g) && (k > 0) -- No newline if no overlap
538 = textBeside_ (Str (spaces k)) k q
539 | otherwise -- Put them really above
540 = nilAbove_ (mkNest k q)
542 -- ---------------------------------------------------------------------------
543 -- Horizontal composition @<>@
545 p <> q = Beside p False q
546 p <+> q = Beside p True q
548 beside :: Doc -> Bool -> RDoc -> RDoc
549 -- Specification: beside g p q = p <g> q
551 beside NoDoc g q = NoDoc
552 beside (p1 `Union` p2) g q = (beside p1 g q) `union_` (beside p2 g q)
554 beside (Nest k p) g q = nest_ k (beside p g q) -- p non-empty
555 beside p@(Beside p1 g1 q1) g2 q2
556 {- (A `op1` B) `op2` C == A `op1` (B `op2` C) iff op1 == op2
557 [ && (op1 == <> || op1 == <+>) ] -}
558 | g1 == g2 = beside p1 g1 (beside q1 g2 q2)
559 | otherwise = beside (reduceDoc p) g2 q2
560 beside p@(Above _ _ _) g q = beside (reduceDoc p) g q
561 beside (NilAbove p) g q = nilAbove_ (beside p g q)
562 beside (TextBeside s sl p) g q = textBeside_ s sl rest
565 Empty -> nilBeside g q
566 other -> beside p g q
569 nilBeside :: Bool -> RDoc -> RDoc
570 -- Specification: text "" <> nilBeside g p
573 nilBeside g Empty = Empty -- Hence the text "" in the spec
574 nilBeside g (Nest _ p) = nilBeside g p
575 nilBeside g p | g = textBeside_ space_text 1 p
578 -- ---------------------------------------------------------------------------
579 -- Separate, @sep@, Hughes version
581 -- Specification: sep ps = oneLiner (hsep ps)
585 sep = sepX True -- Separate with spaces
586 cat = sepX False -- Don't
589 sepX x (p:ps) = sep1 x (reduceDoc p) 0 ps
592 -- Specification: sep1 g k ys = sep (x : map (nest k) ys)
593 -- = oneLiner (x <g> nest k (hsep ys))
594 -- `union` x $$ nest k (vcat ys)
596 sep1 :: Bool -> RDoc -> Int -> [Doc] -> RDoc
597 sep1 g _ k ys | k `seq` False = undefined
598 sep1 g NoDoc k ys = NoDoc
599 sep1 g (p `Union` q) k ys = sep1 g p k ys
601 (aboveNest q False k (reduceDoc (vcat ys)))
603 sep1 g Empty k ys = mkNest k (sepX g ys)
604 sep1 g (Nest n p) k ys = nest_ n (sep1 g p (k - n) ys)
606 sep1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (reduceDoc (vcat ys)))
607 sep1 g (TextBeside s sl p) k ys = textBeside_ s sl (sepNB g p (k - sl) ys)
609 -- Specification: sepNB p k ys = sep1 (text "" <> p) k ys
610 -- Called when we have already found some text in the first item
611 -- We have to eat up nests
613 sepNB g (Nest _ p) k ys = sepNB g p k ys
615 sepNB g Empty k ys = oneLiner (nilBeside g (reduceDoc rest))
617 nilAboveNest False k (reduceDoc (vcat ys))
620 | otherwise = hcat ys
622 sepNB g p k ys = sep1 g p k ys
624 -- ---------------------------------------------------------------------------
633 -- fill (p1:p2:ps) = oneLiner p1 <#> nest (length p1)
634 -- (fill (oneLiner p2 : ps))
639 fill g (p:ps) = fill1 g (reduceDoc p) 0 ps
642 fill1 :: Bool -> RDoc -> Int -> [Doc] -> Doc
643 fill1 g _ k ys | k `seq` False = undefined
644 fill1 g NoDoc k ys = NoDoc
645 fill1 g (p `Union` q) k ys = fill1 g p k ys
647 (aboveNest q False k (fill g ys))
649 fill1 g Empty k ys = mkNest k (fill g ys)
650 fill1 g (Nest n p) k ys = nest_ n (fill1 g p (k - n) ys)
652 fill1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (fill g ys))
653 fill1 g (TextBeside s sl p) k ys = textBeside_ s sl (fillNB g p (k - sl) ys)
655 fillNB g _ k ys | k `seq` False = undefined
656 fillNB g (Nest _ p) k ys = fillNB g p k ys
657 fillNB g Empty k [] = Empty
658 fillNB g Empty k (y:ys) = nilBeside g (fill1 g (oneLiner (reduceDoc y)) k1 ys)
660 nilAboveNest False k (fill g (y:ys))
665 fillNB g p k ys = fill1 g p k ys
668 -- ---------------------------------------------------------------------------
669 -- Selecting the best layout
672 -> Int -- Line length
673 -> Int -- Ribbon length
675 -> RDoc -- No unions in here!
677 best OneLineMode w r p
682 get (NilAbove p) = nilAbove_ (get p)
683 get (TextBeside s sl p) = textBeside_ s sl (get p)
684 get (Nest k p) = get p -- Elide nest
685 get (p `Union` q) = first (get p) (get q)
690 get :: Int -- (Remaining) width of line
692 get w _ | w==0 && False = undefined
695 get w (NilAbove p) = nilAbove_ (get w p)
696 get w (TextBeside s sl p) = textBeside_ s sl (get1 w sl p)
697 get w (Nest k p) = nest_ k (get (w - k) p)
698 get w (p `Union` q) = nicest w r (get w p) (get w q)
700 get1 :: Int -- (Remaining) width of line
701 -> Int -- Amount of first line already eaten up
702 -> Doc -- This is an argument to TextBeside => eat Nests
703 -> Doc -- No unions in here!
705 get1 w _ _ | w==0 && False = undefined
706 get1 w sl Empty = Empty
707 get1 w sl NoDoc = NoDoc
708 get1 w sl (NilAbove p) = nilAbove_ (get (w - sl) p)
709 get1 w sl (TextBeside t tl p) = textBeside_ t tl (get1 w (sl + tl) p)
710 get1 w sl (Nest k p) = get1 w sl p
711 get1 w sl (p `Union` q) = nicest1 w r sl (get1 w sl p)
714 nicest w r p q = nicest1 w r 0 p q
715 nicest1 w r sl p q | fits ((w `minn` r) - sl) p = p
718 fits :: Int -- Space available
720 -> Bool -- True if *first line* of Doc fits in space available
722 fits n p | n < 0 = False
725 fits n (NilAbove _) = True
726 fits n (TextBeside _ sl p) = fits (n - sl) p
731 -- @first@ and @nonEmptySet@ are similar to @nicest@ and @fits@, only simpler.
732 -- @first@ returns its first argument if it is non-empty, otherwise its second.
734 first p q | nonEmptySet p = p
737 nonEmptySet NoDoc = False
738 nonEmptySet (p `Union` q) = True
739 nonEmptySet Empty = True
740 nonEmptySet (NilAbove p) = True -- NoDoc always in first line
741 nonEmptySet (TextBeside _ _ p) = nonEmptySet p
742 nonEmptySet (Nest _ p) = nonEmptySet p
744 -- @oneLiner@ returns the one-line members of the given set of @Doc@s.
746 oneLiner :: Doc -> Doc
747 oneLiner NoDoc = NoDoc
748 oneLiner Empty = Empty
749 oneLiner (NilAbove p) = NoDoc
750 oneLiner (TextBeside s sl p) = textBeside_ s sl (oneLiner p)
751 oneLiner (Nest k p) = nest_ k (oneLiner p)
752 oneLiner (p `Union` q) = oneLiner p
755 -- ---------------------------------------------------------------------------
756 -- Displaying the best layout
759 renderStyle Style{mode, lineLength, ribbonsPerLine} doc
760 = fullRender mode lineLength ribbonsPerLine doc ""
763 render doc = showDoc doc ""
764 showDoc doc rest = fullRender PageMode 100 1.5 string_txt rest doc
766 string_txt (Chr c) s = c:s
767 string_txt (Str s1) s2 = s1 ++ s2
768 string_txt (PStr s1) s2 = s1 ++ s2
771 fullRender OneLineMode _ _ txt end doc = easy_display space_text txt end (reduceDoc doc)
772 fullRender LeftMode _ _ txt end doc = easy_display nl_text txt end (reduceDoc doc)
774 fullRender mode line_length ribbons_per_line txt end doc
775 = display mode line_length ribbon_length txt end best_doc
777 best_doc = best mode hacked_line_length ribbon_length (reduceDoc doc)
779 hacked_line_length, ribbon_length :: Int
780 ribbon_length = round (fromIntegral line_length / ribbons_per_line)
781 hacked_line_length = case mode of { ZigZagMode -> maxBound; other -> line_length }
783 display mode page_width ribbon_width txt end doc
784 = case page_width - ribbon_width of { gap_width ->
785 case gap_width `quot` 2 of { shift ->
787 lay k _ | k `seq` False = undefined
788 lay k (Nest k1 p) = lay (k + k1) p
791 lay k (NilAbove p) = nl_text `txt` lay k p
793 lay k (TextBeside s sl p)
795 ZigZagMode | k >= gap_width
797 Str (multi_ch shift '/') `txt` (
799 lay1 (k - shift) s sl p)))
803 Str (multi_ch shift '\\') `txt` (
805 lay1 (k + shift) s sl p )))
807 other -> lay1 k s sl p
809 lay1 k _ sl _ | k+sl `seq` False = undefined
810 lay1 k s sl p = Str (indent k) `txt` (s `txt` lay2 (k + sl) p)
812 lay2 k _ | k `seq` False = undefined
813 lay2 k (NilAbove p) = nl_text `txt` lay k p
814 lay2 k (TextBeside s sl p) = s `txt` (lay2 (k + sl) p)
815 lay2 k (Nest _ p) = lay2 k p
821 cant_fail = error "easy_display: NoDoc"
822 easy_display nl_text txt end doc
825 lay NoDoc no_doc = no_doc
826 lay (Union p q) no_doc = {- lay p -} (lay q cant_fail) -- Second arg can't be NoDoc
827 lay (Nest k p) no_doc = lay p no_doc
828 lay Empty no_doc = end
829 lay (NilAbove p) no_doc = nl_text `txt` lay p cant_fail -- NoDoc always on first line
830 lay (TextBeside s sl p) no_doc = s `txt` lay p no_doc
832 indent n | n >= 8 = '\t' : indent (n - 8)
833 | otherwise = spaces n
836 multi_ch n ch = ch : multi_ch (n - 1) ch
839 spaces n = ' ' : spaces (n - 1)