1 -----------------------------------------------------------------------------
3 -- Module : Text.PrettyPrint.HughesPJ
4 -- Copyright : (c) The University of Glasgow 2001
5 -- License : BSD-style (see the file libraries/core/LICENSE)
7 -- Maintainer : libraries@haskell.org
8 -- Stability : provisional
9 -- Portability : portable
11 -- $Id: HughesPJ.hs,v 1.2 2002/04/24 16:31:47 simonmar Exp $
13 -- John Hughes's and Simon Peyton Jones's Pretty Printer Combinators
15 -- Based on "The Design of a Pretty-printing Library"
16 -- in Advanced Functional Programming,
17 -- Johan Jeuring and Erik Meijer (eds), LNCS 925
18 -- http://www.cs.chalmers.se/~rjmh/Papers/pretty.ps
20 -- Heavily modified by Simon Peyton Jones, Dec 96
22 -----------------------------------------------------------------------------
25 Version 3.0 28 May 1997
26 * Cured massive performance bug. If you write
28 foldl <> empty (map (text.show) [1..10000])
30 you get quadratic behaviour with V2.0. Why? For just the same
31 reason as you get quadratic behaviour with left-associated (++)
34 This is really bad news. One thing a pretty-printer abstraction
35 should certainly guarantee is insensivity to associativity. It
36 matters: suddenly GHC's compilation times went up by a factor of
37 100 when I switched to the new pretty printer.
39 I fixed it with a bit of a hack (because I wanted to get GHC back
40 on the road). I added two new constructors to the Doc type, Above
46 Then, where I need to get to a "TextBeside" or "NilAbove" form I
47 "force" the Doc to squeeze out these suspended calls to Beside and
48 Above; but in so doing I re-associate. It's quite simple, but I'm
49 not satisfied that I've done the best possible job. I'll send you
50 the code if you are interested.
54 int, integer, float, double, rational,
55 lparen, rparen, lbrack, rbrack, lbrace, rbrace,
57 * fullRender's type signature has changed. Rather than producing a
58 string it now takes an extra couple of arguments that tells it how
59 to glue fragments of output together:
63 -> Float -- Ribbons per line
64 -> (TextDetails -> a -> a) -- What to do with text
65 -> a -- What to do at the end
69 The "fragments" are encapsulated in the TextDetails data type:
71 data TextDetails = Chr Char
75 The Chr and Str constructors are obvious enough. The PStr
76 constructor has a packed string (FAST_STRING) inside it. It's
77 generated by using the new "ptext" export.
79 An advantage of this new setup is that you can get the renderer to
80 do output directly (by passing in a function of type (TextDetails
81 -> IO () -> IO ()), rather than producing a string that you then
85 Version 2.0 24 April 1997
86 * Made empty into a left unit for <> as well as a right unit;
87 it is also now true that
89 which wasn't true before.
91 * Fixed an obscure bug in sep that occassionally gave very wierd behaviour
95 * Corrected and tidied up the laws and invariants
97 ======================================================================
98 Relative to John's original paper, there are the following new features:
100 1. There's an empty document, "empty". It's a left and right unit for
101 both <> and $$, and anywhere in the argument list for
102 sep, hcat, hsep, vcat, fcat etc.
104 It is Really Useful in practice.
106 2. There is a paragraph-fill combinator, fsep, that's much like sep,
107 only it keeps fitting things on one line until itc can't fit any more.
109 3. Some random useful extra combinators are provided.
110 <+> puts its arguments beside each other with a space between them,
111 unless either argument is empty in which case it returns the other
114 hcat is a list version of <>
115 hsep is a list version of <+>
116 vcat is a list version of $$
118 sep (separate) is either like hsep or like vcat, depending on what fits
120 cat is behaves like sep, but it uses <> for horizontal conposition
121 fcat is behaves like fsep, but it uses <> for horizontal conposition
123 These new ones do the obvious things:
124 char, semi, comma, colon, space,
125 parens, brackets, braces,
128 4. The "above" combinator, $$, now overlaps its two arguments if the
129 last line of the top argument stops before the first line of the
132 For example: text "hi" $$ nest 5 "there"
139 There are two places this is really useful
141 a) When making labelled blocks, like this:
142 Left -> code for left
143 Right -> code for right
145 code for longlonglonglabel
146 The block is on the same line as the label if the label is
147 short, but on the next line otherwise.
149 b) When laying out lists like this:
154 which some people like. But if the list fits on one line
155 you want [first, second, third]. You can't do this with
156 John's original combinators, but it's quite easy with the
159 The combinator $+$ gives the original "never-overlap" behaviour.
161 5. Several different renderers are provided:
163 * one that uses cut-marks to avoid deeply-nested documents
164 simply piling up in the right-hand margin
165 * one that ignores indentation (fewer chars output; good for machines)
166 * one that ignores indentation and newlines (ditto, only more so)
168 6. Numerous implementation tidy-ups
169 Use of unboxed data types to speed up the implementation
172 module Text.PrettyPrint.HughesPJ (
174 Mode(..), TextDetails(..),
176 empty, isEmpty, nest,
179 int, integer, float, double, rational,
180 parens, brackets, braces, quotes, doubleQuotes,
181 semi, comma, colon, space, equals,
182 lparen, rparen, lbrack, rbrack, lbrace, rbrace,
184 (<>), (<+>), hcat, hsep,
191 -- renderStyle, -- Haskell 1.3 only
202 -- ---------------------------------------------------------------------------
205 -- 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
227 (<>) :: Doc -> Doc -> Doc -- Beside
228 hcat :: [Doc] -> Doc -- List version of <>
229 (<+>) :: Doc -> Doc -> Doc -- Beside, separated by space
230 hsep :: [Doc] -> Doc -- List version of <+>
232 ($$) :: Doc -> Doc -> Doc -- Above; if there is no
233 -- overlap it "dovetails" the two
234 vcat :: [Doc] -> Doc -- List version of $$
236 cat :: [Doc] -> Doc -- Either hcat or vcat
237 sep :: [Doc] -> Doc -- Either hsep or vcat
238 fcat :: [Doc] -> Doc -- ``Paragraph fill'' version of cat
239 fsep :: [Doc] -> Doc -- ``Paragraph fill'' version of sep
241 nest :: Int -> Doc -> Doc -- Nested
244 -- GHC-specific ones.
246 hang :: Doc -> Int -> Doc -> Doc
247 punctuate :: Doc -> [Doc] -> [Doc] -- punctuate p [d1, ... dn] = [d1 <> p, d2 <> p, ... dn-1 <> p, dn]
250 -- Displaying @Doc@ values.
252 instance Show Doc where
253 showsPrec prec doc cont = showDoc doc cont
255 render :: Doc -> String -- Uses default style
257 -> Int -- Line length
258 -> Float -- Ribbons per line
259 -> (TextDetails -> a -> a) -- What to do with text
260 -> a -- What to do at the end
264 {- When we start using 1.3
265 renderStyle :: Style -> Doc -> String
266 data Style = Style { lineLength :: Int, -- In chars
267 ribbonsPerLine :: Float, -- Ratio of ribbon length to line length
270 style :: Style -- The default style
271 style = Style { lineLength = 100, ribbonsPerLine = 2.5, mode = PageMode }
274 data Mode = PageMode -- Normal
275 | ZigZagMode -- With zig-zag cuts
276 | LeftMode -- No indentation, infinitely long lines
277 | OneLineMode -- All on one line
280 -- ---------------------------------------------------------------------------
283 -- The Doc combinators satisfy the following laws:
288 <a1> (x $$ y) $$ z = x $$ (y $$ z)
296 <b1> (x <> y) <> z = x <> (y <> z)
297 <b2> empty <> x = empty
304 <t1> text s <> text t = text (s++t)
305 <t2> text "" <> x = x, if x non-empty
310 <n2> nest k (nest k' x) = nest (k+k') x
311 <n3> nest k (x <> y) = nest k z <> nest k y
312 <n4> nest k (x $$ y) = nest k x $$ nest k y
313 <n5> nest k empty = empty
314 <n6> x <> nest k y = x <> y, if x non-empty
316 ** Note the side condition on <n6>! It is this that
317 ** makes it OK for empty to be a left unit for <>.
321 <m1> (text s <> x) $$ y = text s <> ((text "" <> x)) $$
324 <m2> (x $$ y) <> z = x $$ (y <> z)
328 Laws for list versions
329 ~~~~~~~~~~~~~~~~~~~~~~
330 <l1> sep (ps++[empty]++qs) = sep (ps ++ qs)
331 ...ditto hsep, hcat, vcat, fill...
333 <l2> nest k (sep ps) = sep (map (nest k) ps)
334 ...ditto hsep, hcat, vcat, fill...
338 <o1> oneLiner (nest k p) = nest k (oneLiner p)
339 <o2> oneLiner (x <> y) = oneLiner x <> oneLiner y
341 You might think that the following verion of <m1> would
344 <3 NO> (text s <> x) $$ y = text s <> ((empty <> x)) $$
347 But it doesn't work, for if x=empty, we would have
349 text s $$ y = text s <> (empty $$ nest (-length s) y)
350 = text s <> nest (-length s) y
353 -- ---------------------------------------------------------------------------
354 -- Simple derived definitions
368 int n = text (show n)
369 integer n = text (show n)
370 float n = text (show n)
371 double n = text (show n)
372 rational n = text (show n)
373 -- SIGBJORN wrote instead:
374 -- rational n = text (show (fromRationalX n))
376 quotes p = char '`' <> p <> char '\''
377 doubleQuotes p = char '"' <> p <> char '"'
378 parens p = char '(' <> p <> char ')'
379 brackets p = char '[' <> p <> char ']'
380 braces p = char '{' <> p <> char '}'
383 hcat = foldr (<>) empty
384 hsep = foldr (<+>) empty
385 vcat = foldr ($$) empty
387 hang d1 n d2 = sep [d1, nest n d2]
390 punctuate p (d:ds) = go d ds
393 go d (e:es) = (d <> p) : go e es
395 -- ---------------------------------------------------------------------------
398 -- A Doc represents a *set* of layouts. A Doc with
399 -- no occurrences of Union or NoDoc represents just one layout.
403 | NilAbove Doc -- text "" $$ x
404 | TextBeside TextDetails !Int Doc -- text s <> x
405 | Nest !Int Doc -- nest k x
406 | Union Doc Doc -- ul `union` ur
407 | NoDoc -- The empty set of documents
408 | Beside Doc Bool Doc -- True <=> space between
409 | Above Doc Bool Doc -- True <=> never overlap
411 type RDoc = Doc -- RDoc is a "reduced Doc", guaranteed not to have a top-level Above or Beside
414 reduceDoc :: Doc -> RDoc
415 reduceDoc (Beside p g q) = beside p g (reduceDoc q)
416 reduceDoc (Above p g q) = above p g (reduceDoc q)
420 data TextDetails = Chr Char
426 -- Here are the invariants:
428 -- * The argument of NilAbove is never Empty. Therefore
429 -- a NilAbove occupies at least two lines.
431 -- * The arugment of @TextBeside@ is never @Nest@.
434 -- * The layouts of the two arguments of @Union@ both flatten to the same
437 -- * The arguments of @Union@ are either @TextBeside@, or @NilAbove@.
439 -- * The right argument of a union cannot be equivalent to the empty set
440 -- (@NoDoc@). If the left argument of a union is equivalent to the
441 -- empty set (@NoDoc@), then the @NoDoc@ appears in the first line.
443 -- * An empty document is always represented by @Empty@. It can't be
444 -- hidden inside a @Nest@, or a @Union@ of two @Empty@s.
446 -- * The first line of every layout in the left argument of @Union@ is
447 -- longer than the first line of any layout in the right argument.
448 -- (1) ensures that the left argument has a first line. In view of
449 -- (3), this invariant means that the right argument must have at
453 -- Arg of a NilAbove is always an RDoc
454 nilAbove_ p = NilAbove p
456 -- Arg of a TextBeside is always an RDoc
457 textBeside_ s sl p = TextBeside s sl p
459 -- Arg of Nest is always an RDoc
462 -- Args of union are always RDocs
463 union_ p q = Union p q
466 -- Notice the difference between
467 -- * NoDoc (no documents)
468 -- * Empty (one empty document; no height and no width)
469 -- * text "" (a document containing the empty string;
470 -- one line high, but has no width)
473 -- ---------------------------------------------------------------------------
474 -- @empty@, @text@, @nest@, @union@
481 char c = textBeside_ (Chr c) 1 Empty
482 text s = case length s of {sl -> textBeside_ (Str s) sl Empty}
483 ptext s = case length s of {sl -> textBeside_ (PStr s) sl Empty}
485 nest k p = mkNest k (reduceDoc p) -- Externally callable version
487 -- mkNest checks for Nest's invariant that it doesn't have an Empty inside it
488 mkNest k _ | k `seq` False = undefined
489 mkNest k (Nest k1 p) = mkNest (k + k1) p
490 mkNest k NoDoc = NoDoc
491 mkNest k Empty = Empty
492 mkNest 0 p = p -- Worth a try!
493 mkNest k p = nest_ k p
495 -- mkUnion checks for an empty document
496 mkUnion Empty q = Empty
497 mkUnion p q = p `union_` q
499 -- ---------------------------------------------------------------------------
500 -- Vertical composition @$$@
502 p $$ q = Above p False q
503 p $+$ q = Above p True q
505 above :: Doc -> Bool -> RDoc -> RDoc
506 above (Above p g1 q1) g2 q2 = above p g1 (above q1 g2 q2)
507 above p@(Beside _ _ _) g q = aboveNest (reduceDoc p) g 0 (reduceDoc q)
508 above p g q = aboveNest p g 0 (reduceDoc q)
510 aboveNest :: RDoc -> Bool -> Int -> RDoc -> RDoc
511 -- Specfication: aboveNest p g k q = p $g$ (nest k q)
513 aboveNest _ _ k _ | k `seq` False = undefined
514 aboveNest NoDoc g k q = NoDoc
515 aboveNest (p1 `Union` p2) g k q = aboveNest p1 g k q `union_`
518 aboveNest Empty g k q = mkNest k q
519 aboveNest (Nest k1 p) g k q = nest_ k1 (aboveNest p g (k - k1) q)
520 -- p can't be Empty, so no need for mkNest
522 aboveNest (NilAbove p) g k q = nilAbove_ (aboveNest p g k q)
523 aboveNest (TextBeside s sl p) g k q = k1 `seq` textBeside_ s sl rest
527 Empty -> nilAboveNest g k1 q
528 other -> aboveNest p g k1 q
531 nilAboveNest :: Bool -> Int -> RDoc -> RDoc
532 -- Specification: text s <> nilaboveNest g k q
533 -- = text s <> (text "" $g$ nest k q)
535 nilAboveNest _ k _ | k `seq` False = undefined
536 nilAboveNest g k Empty = Empty -- Here's why the "text s <>" is in the spec!
537 nilAboveNest g k (Nest k1 q) = nilAboveNest g (k + k1) q
539 nilAboveNest g k q | (not g) && (k > 0) -- No newline if no overlap
540 = textBeside_ (Str (spaces k)) k q
541 | otherwise -- Put them really above
542 = nilAbove_ (mkNest k q)
544 -- ---------------------------------------------------------------------------
545 -- Horizontal composition @<>@
547 p <> q = Beside p False q
548 p <+> q = Beside p True q
550 beside :: Doc -> Bool -> RDoc -> RDoc
551 -- Specification: beside g p q = p <g> q
553 beside NoDoc g q = NoDoc
554 beside (p1 `Union` p2) g q = (beside p1 g q) `union_` (beside p2 g q)
556 beside (Nest k p) g q = nest_ k (beside p g q) -- p non-empty
557 beside p@(Beside p1 g1 q1) g2 q2
558 {- (A `op1` B) `op2` C == A `op1` (B `op2` C) iff op1 == op2
559 [ && (op1 == <> || op1 == <+>) ] -}
560 | g1 == g2 = beside p1 g1 (beside q1 g2 q2)
561 | otherwise = beside (reduceDoc p) g2 q2
562 beside p@(Above _ _ _) g q = beside (reduceDoc p) g q
563 beside (NilAbove p) g q = nilAbove_ (beside p g q)
564 beside (TextBeside s sl p) g q = textBeside_ s sl rest
567 Empty -> nilBeside g q
568 other -> beside p g q
571 nilBeside :: Bool -> RDoc -> RDoc
572 -- Specification: text "" <> nilBeside g p
575 nilBeside g Empty = Empty -- Hence the text "" in the spec
576 nilBeside g (Nest _ p) = nilBeside g p
577 nilBeside g p | g = textBeside_ space_text 1 p
580 -- ---------------------------------------------------------------------------
581 -- Separate, @sep@, Hughes version
583 -- Specification: sep ps = oneLiner (hsep ps)
587 sep = sepX True -- Separate with spaces
588 cat = sepX False -- Don't
591 sepX x (p:ps) = sep1 x (reduceDoc p) 0 ps
594 -- Specification: sep1 g k ys = sep (x : map (nest k) ys)
595 -- = oneLiner (x <g> nest k (hsep ys))
596 -- `union` x $$ nest k (vcat ys)
598 sep1 :: Bool -> RDoc -> Int -> [Doc] -> RDoc
599 sep1 g _ k ys | k `seq` False = undefined
600 sep1 g NoDoc k ys = NoDoc
601 sep1 g (p `Union` q) k ys = sep1 g p k ys
603 (aboveNest q False k (reduceDoc (vcat ys)))
605 sep1 g Empty k ys = mkNest k (sepX g ys)
606 sep1 g (Nest n p) k ys = nest_ n (sep1 g p (k - n) ys)
608 sep1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (reduceDoc (vcat ys)))
609 sep1 g (TextBeside s sl p) k ys = textBeside_ s sl (sepNB g p (k - sl) ys)
611 -- Specification: sepNB p k ys = sep1 (text "" <> p) k ys
612 -- Called when we have already found some text in the first item
613 -- We have to eat up nests
615 sepNB g (Nest _ p) k ys = sepNB g p k ys
617 sepNB g Empty k ys = oneLiner (nilBeside g (reduceDoc rest))
619 nilAboveNest False k (reduceDoc (vcat ys))
622 | otherwise = hcat ys
624 sepNB g p k ys = sep1 g p k ys
626 -- ---------------------------------------------------------------------------
635 -- fill (p1:p2:ps) = oneLiner p1 <#> nest (length p1)
636 -- (fill (oneLiner p2 : ps))
641 fill g (p:ps) = fill1 g (reduceDoc p) 0 ps
644 fill1 :: Bool -> RDoc -> Int -> [Doc] -> Doc
645 fill1 g _ k ys | k `seq` False = undefined
646 fill1 g NoDoc k ys = NoDoc
647 fill1 g (p `Union` q) k ys = fill1 g p k ys
649 (aboveNest q False k (fill g ys))
651 fill1 g Empty k ys = mkNest k (fill g ys)
652 fill1 g (Nest n p) k ys = nest_ n (fill1 g p (k - n) ys)
654 fill1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (fill g ys))
655 fill1 g (TextBeside s sl p) k ys = textBeside_ s sl (fillNB g p (k - sl) ys)
657 fillNB g _ k ys | k `seq` False = undefined
658 fillNB g (Nest _ p) k ys = fillNB g p k ys
659 fillNB g Empty k [] = Empty
660 fillNB g Empty k (y:ys) = nilBeside g (fill1 g (oneLiner (reduceDoc y)) k1 ys)
662 nilAboveNest False k (fill g (y:ys))
667 fillNB g p k ys = fill1 g p k ys
670 -- ---------------------------------------------------------------------------
671 -- Selecting the best layout
674 -> Int -- Line length
675 -> Int -- Ribbon length
677 -> RDoc -- No unions in here!
679 best OneLineMode w r p
684 get (NilAbove p) = nilAbove_ (get p)
685 get (TextBeside s sl p) = textBeside_ s sl (get p)
686 get (Nest k p) = get p -- Elide nest
687 get (p `Union` q) = first (get p) (get q)
692 get :: Int -- (Remaining) width of line
694 get w _ | w==0 && False = undefined
697 get w (NilAbove p) = nilAbove_ (get w p)
698 get w (TextBeside s sl p) = textBeside_ s sl (get1 w sl p)
699 get w (Nest k p) = nest_ k (get (w - k) p)
700 get w (p `Union` q) = nicest w r (get w p) (get w q)
702 get1 :: Int -- (Remaining) width of line
703 -> Int -- Amount of first line already eaten up
704 -> Doc -- This is an argument to TextBeside => eat Nests
705 -> Doc -- No unions in here!
707 get1 w _ _ | w==0 && False = undefined
708 get1 w sl Empty = Empty
709 get1 w sl NoDoc = NoDoc
710 get1 w sl (NilAbove p) = nilAbove_ (get (w - sl) p)
711 get1 w sl (TextBeside t tl p) = textBeside_ t tl (get1 w (sl + tl) p)
712 get1 w sl (Nest k p) = get1 w sl p
713 get1 w sl (p `Union` q) = nicest1 w r sl (get1 w sl p)
716 nicest w r p q = nicest1 w r 0 p q
717 nicest1 w r sl p q | fits ((w `minn` r) - sl) p = p
720 fits :: Int -- Space available
722 -> Bool -- True if *first line* of Doc fits in space available
724 fits n p | n < 0 = False
727 fits n (NilAbove _) = True
728 fits n (TextBeside _ sl p) = fits (n - sl) p
733 -- @first@ and @nonEmptySet@ are similar to @nicest@ and @fits@, only simpler.
734 -- @first@ returns its first argument if it is non-empty, otherwise its second.
736 first p q | nonEmptySet p = p
739 nonEmptySet NoDoc = False
740 nonEmptySet (p `Union` q) = True
741 nonEmptySet Empty = True
742 nonEmptySet (NilAbove p) = True -- NoDoc always in first line
743 nonEmptySet (TextBeside _ _ p) = nonEmptySet p
744 nonEmptySet (Nest _ p) = nonEmptySet p
746 -- @oneLiner@ returns the one-line members of the given set of @Doc@s.
748 oneLiner :: Doc -> Doc
749 oneLiner NoDoc = NoDoc
750 oneLiner Empty = Empty
751 oneLiner (NilAbove p) = NoDoc
752 oneLiner (TextBeside s sl p) = textBeside_ s sl (oneLiner p)
753 oneLiner (Nest k p) = nest_ k (oneLiner p)
754 oneLiner (p `Union` q) = oneLiner p
757 -- ---------------------------------------------------------------------------
758 -- Displaying the best layout
761 renderStyle Style{mode, lineLength, ribbonsPerLine} doc
762 = fullRender mode lineLength ribbonsPerLine doc ""
765 render doc = showDoc doc ""
766 showDoc doc rest = fullRender PageMode 100 1.5 string_txt rest doc
768 string_txt (Chr c) s = c:s
769 string_txt (Str s1) s2 = s1 ++ s2
770 string_txt (PStr s1) s2 = s1 ++ s2
773 fullRender OneLineMode _ _ txt end doc = easy_display space_text txt end (reduceDoc doc)
774 fullRender LeftMode _ _ txt end doc = easy_display nl_text txt end (reduceDoc doc)
776 fullRender mode line_length ribbons_per_line txt end doc
777 = display mode line_length ribbon_length txt end best_doc
779 best_doc = best mode hacked_line_length ribbon_length (reduceDoc doc)
781 hacked_line_length, ribbon_length :: Int
782 ribbon_length = round (fromIntegral line_length / ribbons_per_line)
783 hacked_line_length = case mode of { ZigZagMode -> maxBound; other -> line_length }
785 display mode page_width ribbon_width txt end doc
786 = case page_width - ribbon_width of { gap_width ->
787 case gap_width `quot` 2 of { shift ->
789 lay k _ | k `seq` False = undefined
790 lay k (Nest k1 p) = lay (k + k1) p
793 lay k (NilAbove p) = nl_text `txt` lay k p
795 lay k (TextBeside s sl p)
797 ZigZagMode | k >= gap_width
799 Str (multi_ch shift '/') `txt` (
801 lay1 (k - shift) s sl p)))
805 Str (multi_ch shift '\\') `txt` (
807 lay1 (k + shift) s sl p )))
809 other -> lay1 k s sl p
811 lay1 k _ sl _ | k+sl `seq` False = undefined
812 lay1 k s sl p = Str (indent k) `txt` (s `txt` lay2 (k + sl) p)
814 lay2 k _ | k `seq` False = undefined
815 lay2 k (NilAbove p) = nl_text `txt` lay k p
816 lay2 k (TextBeside s sl p) = s `txt` (lay2 (k + sl) p)
817 lay2 k (Nest _ p) = lay2 k p
823 cant_fail = error "easy_display: NoDoc"
824 easy_display nl_text txt end doc
827 lay NoDoc no_doc = no_doc
828 lay (Union p q) no_doc = {- lay p -} (lay q cant_fail) -- Second arg can't be NoDoc
829 lay (Nest k p) no_doc = lay p no_doc
830 lay Empty no_doc = end
831 lay (NilAbove p) no_doc = nl_text `txt` lay p cant_fail -- NoDoc always on first line
832 lay (TextBeside s sl p) no_doc = s `txt` lay p no_doc
834 indent n | n >= 8 = '\t' : indent (n - 8)
835 | otherwise = spaces n
838 multi_ch n ch = ch : multi_ch (n - 1) ch
841 spaces n = ' ' : spaces (n - 1)