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 #include "HsVersions.h"
182 import Numeric (fromRat)
184 -- Don't import Util( assertPanic ) because it makes a loop in the module structure
193 *********************************************************
195 \subsection{CPP magic so that we can compile with both GHC and Hugs}
197 *********************************************************
199 The library uses unboxed types to get a bit more speed, but these CPP macros
200 allow you to use either GHC or Hugs. To get GHC, just set the CPP variable
205 #if defined(__GLASGOW_HASKELL__)
210 -- Disable ASSERT checks; they are expensive!
211 #define LOCAL_ASSERT(x)
215 #define NEGATE negateInt#
220 #define DIV `quotInt#`
224 #define MAXINT maxBound
230 #define LOCAL_ASSERT(x)
235 #define NEGATE negate
244 #define MAXINT maxBound
251 *********************************************************
253 \subsection{The interface}
255 *********************************************************
257 The primitive @Doc@ values
261 isEmpty :: Doc -> Bool
262 text :: String -> Doc
265 semi, comma, colon, space, equals :: Doc
266 lparen, rparen, lbrack, rbrack, lbrace, rbrace :: Doc
268 parens, brackets, braces :: Doc -> Doc
269 quotes, doubleQuotes :: Doc -> Doc
272 integer :: Integer -> Doc
273 float :: Float -> Doc
274 double :: Double -> Doc
275 rational :: Rational -> Doc
278 Combining @Doc@ values
281 (<>) :: Doc -> Doc -> Doc -- Beside
282 hcat :: [Doc] -> Doc -- List version of <>
283 (<+>) :: Doc -> Doc -> Doc -- Beside, separated by space
284 hsep :: [Doc] -> Doc -- List version of <+>
286 ($$) :: Doc -> Doc -> Doc -- Above; if there is no
287 -- overlap it "dovetails" the two
288 vcat :: [Doc] -> Doc -- List version of $$
290 cat :: [Doc] -> Doc -- Either hcat or vcat
291 sep :: [Doc] -> Doc -- Either hsep or vcat
292 fcat :: [Doc] -> Doc -- ``Paragraph fill'' version of cat
293 fsep :: [Doc] -> Doc -- ``Paragraph fill'' version of sep
295 nest :: Int -> Doc -> Doc -- Nested
301 hang :: Doc -> Int -> Doc -> Doc
302 punctuate :: Doc -> [Doc] -> [Doc] -- punctuate p [d1, ... dn] = [d1 <> p, d2 <> p, ... dn-1 <> p, dn]
305 Displaying @Doc@ values.
308 instance SHOW Doc where
309 showsPrec prec doc cont = showDoc doc cont
311 render :: Doc -> String -- Uses default style
313 -> Int -- Line length
314 -> Float -- Ribbons per line
315 -> (TextDetails -> a -> a) -- What to do with text
316 -> a -- What to do at the end
320 {- When we start using 1.3
321 renderStyle :: Style -> Doc -> String
322 data Style = Style { lineLength :: Int, -- In chars
323 ribbonsPerLine :: Float, -- Ratio of ribbon length to line length
326 style :: Style -- The default style
327 style = Style { lineLength = 100, ribbonsPerLine = 2.5, mode = PageMode }
330 data Mode = PageMode -- Normal
331 | ZigZagMode -- With zig-zag cuts
332 | LeftMode -- No indentation, infinitely long lines
333 | OneLineMode -- All on one line
338 *********************************************************
340 \subsection{The @Doc@ calculus}
342 *********************************************************
344 The @Doc@ combinators satisfy the following laws:
348 <a1> (x $$ y) $$ z = x $$ (y $$ z)
356 <b1> (x <> y) <> z = x <> (y <> z)
357 <b2> empty <> x = empty
364 <t1> text s <> text t = text (s++t)
365 <t2> text "" <> x = x, if x non-empty
370 <n2> nest k (nest k' x) = nest (k+k') x
371 <n3> nest k (x <> y) = nest k z <> nest k y
372 <n4> nest k (x $$ y) = nest k x $$ nest k y
373 <n5> nest k empty = empty
374 <n6> x <> nest k y = x <> y, if x non-empty
376 ** Note the side condition on <n6>! It is this that
377 ** makes it OK for empty to be a left unit for <>.
381 <m1> (text s <> x) $$ y = text s <> ((text "" <> x)) $$
384 <m2> (x $$ y) <> z = x $$ (y <> z)
388 Laws for list versions
389 ~~~~~~~~~~~~~~~~~~~~~~
390 <l1> sep (ps++[empty]++qs) = sep (ps ++ qs)
391 ...ditto hsep, hcat, vcat, fill...
393 <l2> nest k (sep ps) = sep (map (nest k) ps)
394 ...ditto hsep, hcat, vcat, fill...
398 <o1> oneLiner (nest k p) = nest k (oneLiner p)
399 <o2> oneLiner (x <> y) = oneLiner x <> oneLiner y
403 You might think that the following verion of <m1> would
406 <3 NO> (text s <> x) $$ y = text s <> ((empty <> x)) $$
409 But it doesn't work, for if x=empty, we would have
411 text s $$ y = text s <> (empty $$ nest (-length s) y)
412 = text s <> nest (-length s) y
417 *********************************************************
419 \subsection{Simple derived definitions}
421 *********************************************************
436 int n = text (show n)
437 integer n = text (show n)
438 float n = text (show n)
439 double n = text (show n)
440 rational n = text (show (fromRat n))
441 --rational n = text (show (fromRationalX n)) -- _showRational 30 n)
443 quotes p = char '`' <> p <> char '\''
444 doubleQuotes p = char '"' <> p <> char '"'
445 parens p = char '(' <> p <> char ')'
446 brackets p = char '[' <> p <> char ']'
447 braces p = char '{' <> p <> char '}'
450 hcat = foldr (<>) empty
451 hsep = foldr (<+>) empty
452 vcat = foldr ($$) empty
454 hang d1 n d2 = sep [d1, nest n d2]
457 punctuate p (d:ds) = go d ds
460 go d (e:es) = (d <> p) : go e es
464 *********************************************************
466 \subsection{The @Doc@ data type}
468 *********************************************************
470 A @Doc@ represents a {\em set} of layouts. A @Doc@ with
471 no occurrences of @Union@ or @NoDoc@ represents just one layout.
475 | NilAbove Doc -- text "" $$ x
476 | TextBeside TextDetails INT Doc -- text s <> x
477 | Nest INT Doc -- nest k x
478 | Union Doc Doc -- ul `union` ur
479 | NoDoc -- The empty set of documents
480 | Beside Doc Bool Doc -- True <=> space between
481 | Above Doc Bool Doc -- True <=> never overlap
483 type RDoc = Doc -- RDoc is a "reduced Doc", guaranteed not to have a top-level Above or Beside
486 reduceDoc :: Doc -> RDoc
487 reduceDoc (Beside p g q) = beside p g (reduceDoc q)
488 reduceDoc (Above p g q) = above p g (reduceDoc q)
492 data TextDetails = Chr Char
499 Here are the invariants:
502 The argument of @NilAbove@ is never @Empty@. Therefore
503 a @NilAbove@ occupies at least two lines.
506 The arugment of @TextBeside@ is never @Nest@.
509 The layouts of the two arguments of @Union@ both flatten to the same string.
512 The arguments of @Union@ are either @TextBeside@, or @NilAbove@.
515 The right argument of a union cannot be equivalent to the empty set (@NoDoc@).
516 If the left argument of a union is equivalent to the empty set (@NoDoc@),
517 then the @NoDoc@ appears in the first line.
520 An empty document is always represented by @Empty@.
521 It can't be hidden inside a @Nest@, or a @Union@ of two @Empty@s.
524 The first line of every layout in the left argument of @Union@
525 is longer than the first line of any layout in the right argument.
526 (1) ensures that the left argument has a first line. In view of (3),
527 this invariant means that the right argument must have at least two
532 -- Arg of a NilAbove is always an RDoc
533 nilAbove_ p = LOCAL_ASSERT( ok p ) NilAbove p
538 -- Arg of a TextBeside is always an RDoc
539 textBeside_ s sl p = TextBeside s sl (LOCAL_ASSERT( ok p ) p)
541 ok (Nest _ _) = False
544 -- Arg of Nest is always an RDoc
545 nest_ k p = Nest k (LOCAL_ASSERT( ok p ) p)
550 -- Args of union are always RDocs
551 union_ p q = Union (LOCAL_ASSERT( ok p ) p) (LOCAL_ASSERT( ok q ) q)
553 ok (TextBeside _ _ _) = True
554 ok (NilAbove _) = True
555 ok (Union _ _) = True
560 Notice the difference between
561 * NoDoc (no documents)
562 * Empty (one empty document; no height and no width)
563 * text "" (a document containing the empty string;
564 one line high, but has no width)
568 *********************************************************
570 \subsection{@empty@, @text@, @nest@, @union@}
572 *********************************************************
580 char c = textBeside_ (Chr c) 1# Empty
581 text s = case length s of {IBOX(sl) -> textBeside_ (Str s) sl Empty}
582 ptext s = case _LENGTH_ s of {IBOX(sl) -> textBeside_ (PStr s) sl Empty}
584 nest IBOX(k) p = mkNest k (reduceDoc p) -- Externally callable version
586 -- mkNest checks for Nest's invariant that it doesn't have an Empty inside it
587 mkNest k (Nest k1 p) = mkNest (k PLUS k1) p
588 mkNest k NoDoc = NoDoc
589 mkNest k Empty = Empty
590 mkNest ILIT(0) p = p -- Worth a try!
591 mkNest k p = nest_ k p
593 -- mkUnion checks for an empty document
594 mkUnion Empty q = Empty
595 mkUnion p q = p `union_` q
598 *********************************************************
600 \subsection{Vertical composition @$$@}
602 *********************************************************
606 p $$ q = Above p False q
607 p $+$ q = Above p True q
609 above :: Doc -> Bool -> RDoc -> RDoc
610 above (Above p g1 q1) g2 q2 = above p g1 (above q1 g2 q2)
611 above p@(Beside _ _ _) g q = aboveNest (reduceDoc p) g ILIT(0) (reduceDoc q)
612 above p g q = aboveNest p g ILIT(0) (reduceDoc q)
614 aboveNest :: RDoc -> Bool -> INT -> RDoc -> RDoc
615 -- Specfication: aboveNest p g k q = p $g$ (nest k q)
617 aboveNest NoDoc g k q = NoDoc
618 aboveNest (p1 `Union` p2) g k q = aboveNest p1 g k q `union_`
621 aboveNest Empty g k q = mkNest k q
622 aboveNest (Nest k1 p) g k q = nest_ k1 (aboveNest p g (k MINUS k1) q)
623 -- p can't be Empty, so no need for mkNest
625 aboveNest (NilAbove p) g k q = nilAbove_ (aboveNest p g k q)
626 aboveNest (TextBeside s sl p) g k q = textBeside_ s sl rest
630 Empty -> nilAboveNest g k1 q
631 other -> aboveNest p g k1 q
635 nilAboveNest :: Bool -> INT -> RDoc -> RDoc
636 -- Specification: text s <> nilaboveNest g k q
637 -- = text s <> (text "" $g$ nest k q)
639 nilAboveNest g k Empty = Empty -- Here's why the "text s <>" is in the spec!
640 nilAboveNest g k (Nest k1 q) = nilAboveNest g (k PLUS k1) q
642 nilAboveNest g k q | (not g) && (k GR ILIT(0)) -- No newline if no overlap
643 = textBeside_ (Str (spaces k)) k q
644 | otherwise -- Put them really above
645 = nilAbove_ (mkNest k q)
649 *********************************************************
651 \subsection{Horizontal composition @<>@}
653 *********************************************************
656 p <> q = Beside p False q
657 p <+> q = Beside p True q
659 beside :: Doc -> Bool -> RDoc -> RDoc
660 -- Specification: beside g p q = p <g> q
662 beside NoDoc g q = NoDoc
663 beside (p1 `Union` p2) g q = (beside p1 g q) `union_` (beside p2 g q)
665 beside (Nest k p) g q = nest_ k (beside p g q) -- p non-empty
666 beside p@(Beside p1 g1 q1) g2 q2
667 {- (A `op1` B) `op2` C == A `op1` (B `op2` C) iff op1 == op2
668 [ && (op1 == <> || op1 == <+>) ] -}
669 | g1 == g2 = beside p1 g1 (beside q1 g2 q2)
670 | otherwise = beside (reduceDoc p) g2 q2
671 beside p@(Above _ _ _) g q = beside (reduceDoc p) g q
672 beside (NilAbove p) g q = nilAbove_ (beside p g q)
673 beside (TextBeside s sl p) g q = textBeside_ s sl rest
676 Empty -> nilBeside g q
677 other -> beside p g q
681 nilBeside :: Bool -> RDoc -> RDoc
682 -- Specification: text "" <> nilBeside g p
685 nilBeside g Empty = Empty -- Hence the text "" in the spec
686 nilBeside g (Nest _ p) = nilBeside g p
687 nilBeside g p | g = textBeside_ space_text ILIT(1) p
691 *********************************************************
693 \subsection{Separate, @sep@, Hughes version}
695 *********************************************************
698 -- Specification: sep ps = oneLiner (hsep ps)
702 sep = sepX True -- Separate with spaces
703 cat = sepX False -- Don't
706 sepX x (p:ps) = sep1 x (reduceDoc p) ILIT(0) ps
709 -- Specification: sep1 g k ys = sep (x : map (nest k) ys)
710 -- = oneLiner (x <g> nest k (hsep ys))
711 -- `union` x $$ nest k (vcat ys)
713 sep1 :: Bool -> RDoc -> INT -> [Doc] -> RDoc
714 sep1 g NoDoc k ys = NoDoc
715 sep1 g (p `Union` q) k ys = sep1 g p k ys
717 (aboveNest q False k (reduceDoc (vcat ys)))
719 sep1 g Empty k ys = mkNest k (sepX g ys)
720 sep1 g (Nest n p) k ys = nest_ n (sep1 g p (k MINUS n) ys)
722 sep1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (reduceDoc (vcat ys)))
723 sep1 g (TextBeside s sl p) k ys = textBeside_ s sl (sepNB g p (k MINUS sl) ys)
725 -- Specification: sepNB p k ys = sep1 (text "" <> p) k ys
726 -- Called when we have already found some text in the first item
727 -- We have to eat up nests
729 sepNB g (Nest _ p) k ys = sepNB g p k ys
731 sepNB g Empty k ys = oneLiner (nilBeside g (reduceDoc rest))
733 nilAboveNest False k (reduceDoc (vcat ys))
736 | otherwise = hcat ys
738 sepNB g p k ys = sep1 g p k ys
741 *********************************************************
745 *********************************************************
754 -- fill (p1:p2:ps) = oneLiner p1 <#> nest (length p1)
755 -- (fill (oneLiner p2 : ps))
760 fill g (p:ps) = fill1 g (reduceDoc p) ILIT(0) ps
763 fill1 :: Bool -> RDoc -> INT -> [Doc] -> Doc
764 fill1 g NoDoc k ys = NoDoc
765 fill1 g (p `Union` q) k ys = fill1 g p k ys
767 (aboveNest q False k (fill g ys))
769 fill1 g Empty k ys = mkNest k (fill g ys)
770 fill1 g (Nest n p) k ys = nest_ n (fill1 g p (k MINUS n) ys)
772 fill1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (fill g ys))
773 fill1 g (TextBeside s sl p) k ys = textBeside_ s sl (fillNB g p (k MINUS sl) ys)
775 fillNB g (Nest _ p) k ys = fillNB g p k ys
776 fillNB g Empty k [] = Empty
777 fillNB g Empty k (y:ys) = nilBeside g (fill1 g (oneLiner (reduceDoc y)) k1 ys)
779 nilAboveNest False k (fill g (y:ys))
781 k1 | g = k MINUS ILIT(1)
784 fillNB g p k ys = fill1 g p k ys
788 *********************************************************
790 \subsection{Selecting the best layout}
792 *********************************************************
795 best :: Int -- Line length
796 -> Int -- Ribbon length
798 -> RDoc -- No unions in here!
800 best IBOX(w) IBOX(r) p
803 get :: INT -- (Remaining) width of line
807 get w (NilAbove p) = nilAbove_ (get w p)
808 get w (TextBeside s sl p) = textBeside_ s sl (get1 w sl p)
809 get w (Nest k p) = nest_ k (get (w MINUS k) p)
810 get w (p `Union` q) = nicest w r (get w p) (get w q)
812 get1 :: INT -- (Remaining) width of line
813 -> INT -- Amount of first line already eaten up
814 -> Doc -- This is an argument to TextBeside => eat Nests
815 -> Doc -- No unions in here!
817 get1 w sl Empty = Empty
818 get1 w sl NoDoc = NoDoc
819 get1 w sl (NilAbove p) = nilAbove_ (get (w MINUS sl) p)
820 get1 w sl (TextBeside t tl p) = textBeside_ t tl (get1 w (sl PLUS tl) p)
821 get1 w sl (Nest k p) = get1 w sl p
822 get1 w sl (p `Union` q) = nicest1 w r sl (get1 w sl p)
825 nicest w r p q = nicest1 w r ILIT(0) p q
826 nicest1 w r sl p q | fits ((w `minn` r) MINUS sl) p = p
829 fits :: INT -- Space available
831 -> Bool -- True if *first line* of Doc fits in space available
833 fits n p | n LT ILIT(0) = False
836 fits n (NilAbove _) = True
837 fits n (TextBeside _ sl p) = fits (n MINUS sl) p
839 minn x y | x LT y = x
843 @first@ and @nonEmptySet@ are similar to @nicest@ and @fits@, only simpler.
844 @first@ returns its first argument if it is non-empty, otherwise its second.
847 first p q | nonEmptySet p = p
850 nonEmptySet NoDoc = False
851 nonEmptySet (p `Union` q) = True
852 nonEmptySet Empty = True
853 nonEmptySet (NilAbove p) = True -- NoDoc always in first line
854 nonEmptySet (TextBeside _ _ p) = nonEmptySet p
855 nonEmptySet (Nest _ p) = nonEmptySet p
858 @oneLiner@ returns the one-line members of the given set of @Doc@s.
861 oneLiner :: Doc -> Doc
862 oneLiner NoDoc = NoDoc
863 oneLiner Empty = Empty
864 oneLiner (NilAbove p) = NoDoc
865 oneLiner (TextBeside s sl p) = textBeside_ s sl (oneLiner p)
866 oneLiner (Nest k p) = nest_ k (oneLiner p)
867 oneLiner (p `Union` q) = oneLiner p
872 *********************************************************
874 \subsection{Displaying the best layout}
876 *********************************************************
881 renderStyle Style{mode, lineLength, ribbonsPerLine} doc
882 = fullRender mode lineLength ribbonsPerLine doc ""
885 render doc = showDoc doc ""
886 showDoc doc rest = fullRender PageMode 100 1.5 string_txt rest doc
888 string_txt (Chr c) s = c:s
889 string_txt (Str s1) s2 = s1 ++ s2
890 string_txt (PStr s1) s2 = _UNPK_ s1 ++ s2
895 fullRender OneLineMode _ _ txt end doc
896 = lay (reduceDoc doc)
898 lay NoDoc = cant_fail
899 lay (Union p q) = (lay q) -- Second arg can't be NoDoc
900 lay (Nest k p) = lay p
902 lay (NilAbove p) = space_text `txt` lay p -- NoDoc always on first line
903 lay (TextBeside s sl p) = s `txt` lay p
905 fullRender LeftMode _ _ txt end doc
906 = lay (reduceDoc doc)
908 lay NoDoc = cant_fail
909 lay (Union p q) = lay (first p q)
910 lay (Nest k p) = lay p
912 lay (NilAbove p) = nl_text `txt` lay p -- NoDoc always on first line
913 lay (TextBeside s sl p) = s `txt` lay p
915 fullRender mode line_length ribbons_per_line txt end doc
916 = display mode line_length ribbon_length txt end best_doc
918 best_doc = best hacked_line_length ribbon_length (reduceDoc doc)
920 hacked_line_length, ribbon_length :: Int
921 ribbon_length = round (fromInt line_length / ribbons_per_line)
922 hacked_line_length = case mode of { ZigZagMode -> MAXINT; other -> line_length }
924 display mode IBOX(page_width) IBOX(ribbon_width) txt end doc
925 = case page_width MINUS ribbon_width of { gap_width ->
926 case gap_width DIV ILIT(2) of { shift ->
928 lay k (Nest k1 p) = lay (k PLUS k1) p
931 lay k (NilAbove p) = nl_text `txt` lay k p
933 lay k (TextBeside s sl p)
935 ZigZagMode | k GREQ gap_width
937 Str (multi_ch shift '/') `txt` (
939 lay1 (k MINUS shift) s sl p)))
943 Str (multi_ch shift '\\') `txt` (
945 lay1 (k PLUS shift) s sl p )))
947 other -> lay1 k s sl p
949 lay1 k s sl p = Str (indent k) `txt` (s `txt` lay2 (k PLUS sl) p)
951 lay2 k (NilAbove p) = nl_text `txt` lay k p
952 lay2 k (TextBeside s sl p) = s `txt` (lay2 (k PLUS sl) p)
953 lay2 k (Nest _ p) = lay2 k p
959 cant_fail = error "easy_display: NoDoc"
961 indent n | n GREQ ILIT(8) = '\t' : indent (n MINUS ILIT(8))
962 | otherwise = spaces n
964 multi_ch ILIT(0) ch = ""
965 multi_ch n ch = ch : multi_ch (n MINUS ILIT(1)) ch
968 spaces n = ' ' : spaces (n MINUS ILIT(1))