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
175 render, fullRender, printDoc
178 #include "HsVersions.h"
182 import Numeric (fromRat)
185 -- Don't import Util( assertPanic ) because it makes a loop in the module structure
194 *********************************************************
196 \subsection{CPP magic so that we can compile with both GHC and Hugs}
198 *********************************************************
200 The library uses unboxed types to get a bit more speed, but these CPP macros
201 allow you to use either GHC or Hugs. To get GHC, just set the CPP variable
206 #if defined(__GLASGOW_HASKELL__)
210 -- Disable ASSERT checks; they are expensive!
211 #define LOCAL_ASSERT(x)
214 #define IBOX(x) (I# (x))
217 #define NEGATE negateInt#
222 #define DIV `quotInt#`
226 #define MAXINT maxBound
232 #define LOCAL_ASSERT(x)
237 #define NEGATE negate
246 #define MAXINT maxBound
253 *********************************************************
255 \subsection{The interface}
257 *********************************************************
259 The primitive @Doc@ values
263 isEmpty :: Doc -> Bool
264 text :: String -> Doc
267 semi, comma, colon, space, equals :: Doc
268 lparen, rparen, lbrack, rbrack, lbrace, rbrace :: Doc
270 parens, brackets, braces :: Doc -> Doc
271 quotes, doubleQuotes :: Doc -> Doc
274 integer :: Integer -> Doc
275 float :: Float -> Doc
276 double :: Double -> Doc
277 rational :: Rational -> Doc
280 Combining @Doc@ values
283 (<>) :: Doc -> Doc -> Doc -- Beside
284 hcat :: [Doc] -> Doc -- List version of <>
285 (<+>) :: Doc -> Doc -> Doc -- Beside, separated by space
286 hsep :: [Doc] -> Doc -- List version of <+>
288 ($$) :: Doc -> Doc -> Doc -- Above; if there is no
289 -- overlap it "dovetails" the two
290 vcat :: [Doc] -> Doc -- List version of $$
292 cat :: [Doc] -> Doc -- Either hcat or vcat
293 sep :: [Doc] -> Doc -- Either hsep or vcat
294 fcat :: [Doc] -> Doc -- ``Paragraph fill'' version of cat
295 fsep :: [Doc] -> Doc -- ``Paragraph fill'' version of sep
297 nest :: Int -> Doc -> Doc -- Nested
303 hang :: Doc -> Int -> Doc -> Doc
304 punctuate :: Doc -> [Doc] -> [Doc] -- punctuate p [d1, ... dn] = [d1 <> p, d2 <> p, ... dn-1 <> p, dn]
307 Displaying @Doc@ values.
310 instance SHOW Doc where
311 showsPrec prec doc cont = showDoc doc cont
313 render :: Doc -> String -- Uses default style
315 -> Int -- Line length
316 -> Float -- Ribbons per line
317 -> (TextDetails -> a -> a) -- What to do with text
318 -> a -- What to do at the end
322 {- When we start using 1.3
323 renderStyle :: Style -> Doc -> String
324 data Style = Style { lineLength :: Int, -- In chars
325 ribbonsPerLine :: Float, -- Ratio of ribbon length to line length
328 style :: Style -- The default style
329 style = Style { lineLength = 100, ribbonsPerLine = 2.5, mode = PageMode }
332 data Mode = PageMode -- Normal
333 | ZigZagMode -- With zig-zag cuts
334 | LeftMode -- No indentation, infinitely long lines
335 | OneLineMode -- All on one line
340 *********************************************************
342 \subsection{The @Doc@ calculus}
344 *********************************************************
346 The @Doc@ combinators satisfy the following laws:
350 <a1> (x $$ y) $$ z = x $$ (y $$ z)
358 <b1> (x <> y) <> z = x <> (y <> z)
359 <b2> empty <> x = empty
366 <t1> text s <> text t = text (s++t)
367 <t2> text "" <> x = x, if x non-empty
372 <n2> nest k (nest k' x) = nest (k+k') x
373 <n3> nest k (x <> y) = nest k z <> nest k y
374 <n4> nest k (x $$ y) = nest k x $$ nest k y
375 <n5> nest k empty = empty
376 <n6> x <> nest k y = x <> y, if x non-empty
378 ** Note the side condition on <n6>! It is this that
379 ** makes it OK for empty to be a left unit for <>.
383 <m1> (text s <> x) $$ y = text s <> ((text "" <> x)) $$
386 <m2> (x $$ y) <> z = x $$ (y <> z)
390 Laws for list versions
391 ~~~~~~~~~~~~~~~~~~~~~~
392 <l1> sep (ps++[empty]++qs) = sep (ps ++ qs)
393 ...ditto hsep, hcat, vcat, fill...
395 <l2> nest k (sep ps) = sep (map (nest k) ps)
396 ...ditto hsep, hcat, vcat, fill...
400 <o1> oneLiner (nest k p) = nest k (oneLiner p)
401 <o2> oneLiner (x <> y) = oneLiner x <> oneLiner y
405 You might think that the following verion of <m1> would
408 <3 NO> (text s <> x) $$ y = text s <> ((empty <> x)) $$
411 But it doesn't work, for if x=empty, we would have
413 text s $$ y = text s <> (empty $$ nest (-length s) y)
414 = text s <> nest (-length s) y
419 *********************************************************
421 \subsection{Simple derived definitions}
423 *********************************************************
438 int n = text (show n)
439 integer n = text (show n)
440 float n = text (show n)
441 double n = text (show n)
442 rational n = text (show (fromRat n))
443 --rational n = text (show (fromRationalX n)) -- _showRational 30 n)
445 quotes p = char '`' <> p <> char '\''
446 doubleQuotes p = char '"' <> p <> char '"'
447 parens p = char '(' <> p <> char ')'
448 brackets p = char '[' <> p <> char ']'
449 braces p = char '{' <> p <> char '}'
452 hcat = foldr (<>) empty
453 hsep = foldr (<+>) empty
454 vcat = foldr ($$) empty
456 hang d1 n d2 = sep [d1, nest n d2]
459 punctuate p (d:ds) = go d ds
462 go d (e:es) = (d <> p) : go e es
466 *********************************************************
468 \subsection{The @Doc@ data type}
470 *********************************************************
472 A @Doc@ represents a {\em set} of layouts. A @Doc@ with
473 no occurrences of @Union@ or @NoDoc@ represents just one layout.
477 | NilAbove Doc -- text "" $$ x
478 | TextBeside TextDetails INT Doc -- text s <> x
479 | Nest INT Doc -- nest k x
480 | Union Doc Doc -- ul `union` ur
481 | NoDoc -- The empty set of documents
482 | Beside Doc Bool Doc -- True <=> space between
483 | Above Doc Bool Doc -- True <=> never overlap
485 type RDoc = Doc -- RDoc is a "reduced Doc", guaranteed not to have a top-level Above or Beside
488 reduceDoc :: Doc -> RDoc
489 reduceDoc (Beside p g q) = beside p g (reduceDoc q)
490 reduceDoc (Above p g q) = above p g (reduceDoc q)
494 data TextDetails = Chr Char
501 Here are the invariants:
504 The argument of @NilAbove@ is never @Empty@. Therefore
505 a @NilAbove@ occupies at least two lines.
508 The arugment of @TextBeside@ is never @Nest@.
511 The layouts of the two arguments of @Union@ both flatten to the same string.
514 The arguments of @Union@ are either @TextBeside@, or @NilAbove@.
517 The right argument of a union cannot be equivalent to the empty set (@NoDoc@).
518 If the left argument of a union is equivalent to the empty set (@NoDoc@),
519 then the @NoDoc@ appears in the first line.
522 An empty document is always represented by @Empty@.
523 It can't be hidden inside a @Nest@, or a @Union@ of two @Empty@s.
526 The first line of every layout in the left argument of @Union@
527 is longer than the first line of any layout in the right argument.
528 (1) ensures that the left argument has a first line. In view of (3),
529 this invariant means that the right argument must have at least two
534 -- Arg of a NilAbove is always an RDoc
535 nilAbove_ p = LOCAL_ASSERT( ok p ) NilAbove p
540 -- Arg of a TextBeside is always an RDoc
541 textBeside_ s sl p = TextBeside s sl (LOCAL_ASSERT( ok p ) p)
543 ok (Nest _ _) = False
546 -- Arg of Nest is always an RDoc
547 nest_ k p = Nest k (LOCAL_ASSERT( ok p ) p)
552 -- Args of union are always RDocs
553 union_ p q = Union (LOCAL_ASSERT( ok p ) p) (LOCAL_ASSERT( ok q ) q)
555 ok (TextBeside _ _ _) = True
556 ok (NilAbove _) = True
557 ok (Union _ _) = True
562 Notice the difference between
563 * NoDoc (no documents)
564 * Empty (one empty document; no height and no width)
565 * text "" (a document containing the empty string;
566 one line high, but has no width)
570 *********************************************************
572 \subsection{@empty@, @text@, @nest@, @union@}
574 *********************************************************
582 char c = textBeside_ (Chr c) 1# Empty
583 text s = case length s of {IBOX(sl) -> textBeside_ (Str s) sl Empty}
584 ptext s = case _LENGTH_ s of {IBOX(sl) -> textBeside_ (PStr s) sl Empty}
586 nest IBOX(k) p = mkNest k (reduceDoc p) -- Externally callable version
588 -- mkNest checks for Nest's invariant that it doesn't have an Empty inside it
589 mkNest k (Nest k1 p) = mkNest (k PLUS k1) p
590 mkNest k NoDoc = NoDoc
591 mkNest k Empty = Empty
592 mkNest ILIT(0) p = p -- Worth a try!
593 mkNest k p = nest_ k p
595 -- mkUnion checks for an empty document
596 mkUnion Empty q = Empty
597 mkUnion p q = p `union_` q
600 *********************************************************
602 \subsection{Vertical composition @$$@}
604 *********************************************************
608 p $$ q = Above p False q
609 p $+$ q = Above p True q
611 above :: Doc -> Bool -> RDoc -> RDoc
612 above (Above p g1 q1) g2 q2 = above p g1 (above q1 g2 q2)
613 above p@(Beside _ _ _) g q = aboveNest (reduceDoc p) g ILIT(0) (reduceDoc q)
614 above p g q = aboveNest p g ILIT(0) (reduceDoc q)
616 aboveNest :: RDoc -> Bool -> INT -> RDoc -> RDoc
617 -- Specfication: aboveNest p g k q = p $g$ (nest k q)
619 aboveNest NoDoc g k q = NoDoc
620 aboveNest (p1 `Union` p2) g k q = aboveNest p1 g k q `union_`
623 aboveNest Empty g k q = mkNest k q
624 aboveNest (Nest k1 p) g k q = nest_ k1 (aboveNest p g (k MINUS k1) q)
625 -- p can't be Empty, so no need for mkNest
627 aboveNest (NilAbove p) g k q = nilAbove_ (aboveNest p g k q)
628 aboveNest (TextBeside s sl p) g k q = textBeside_ s sl rest
632 Empty -> nilAboveNest g k1 q
633 other -> aboveNest p g k1 q
637 nilAboveNest :: Bool -> INT -> RDoc -> RDoc
638 -- Specification: text s <> nilaboveNest g k q
639 -- = text s <> (text "" $g$ nest k q)
641 nilAboveNest g k Empty = Empty -- Here's why the "text s <>" is in the spec!
642 nilAboveNest g k (Nest k1 q) = nilAboveNest g (k PLUS k1) q
644 nilAboveNest g k q | (not g) && (k GR ILIT(0)) -- No newline if no overlap
645 = textBeside_ (Str (spaces k)) k q
646 | otherwise -- Put them really above
647 = nilAbove_ (mkNest k q)
651 *********************************************************
653 \subsection{Horizontal composition @<>@}
655 *********************************************************
658 p <> q = Beside p False q
659 p <+> q = Beside p True q
661 beside :: Doc -> Bool -> RDoc -> RDoc
662 -- Specification: beside g p q = p <g> q
664 beside NoDoc g q = NoDoc
665 beside (p1 `Union` p2) g q = (beside p1 g q) `union_` (beside p2 g q)
667 beside (Nest k p) g q = nest_ k (beside p g q) -- p non-empty
668 beside p@(Beside p1 g1 q1) g2 q2
669 {- (A `op1` B) `op2` C == A `op1` (B `op2` C) iff op1 == op2
670 [ && (op1 == <> || op1 == <+>) ] -}
671 | g1 == g2 = beside p1 g1 (beside q1 g2 q2)
672 | otherwise = beside (reduceDoc p) g2 q2
673 beside p@(Above _ _ _) g q = beside (reduceDoc p) g q
674 beside (NilAbove p) g q = nilAbove_ (beside p g q)
675 beside (TextBeside s sl p) g q = textBeside_ s sl rest
678 Empty -> nilBeside g q
679 other -> beside p g q
683 nilBeside :: Bool -> RDoc -> RDoc
684 -- Specification: text "" <> nilBeside g p
687 nilBeside g Empty = Empty -- Hence the text "" in the spec
688 nilBeside g (Nest _ p) = nilBeside g p
689 nilBeside g p | g = textBeside_ space_text ILIT(1) p
693 *********************************************************
695 \subsection{Separate, @sep@, Hughes version}
697 *********************************************************
700 -- Specification: sep ps = oneLiner (hsep ps)
704 sep = sepX True -- Separate with spaces
705 cat = sepX False -- Don't
708 sepX x (p:ps) = sep1 x (reduceDoc p) ILIT(0) ps
711 -- Specification: sep1 g k ys = sep (x : map (nest k) ys)
712 -- = oneLiner (x <g> nest k (hsep ys))
713 -- `union` x $$ nest k (vcat ys)
715 sep1 :: Bool -> RDoc -> INT -> [Doc] -> RDoc
716 sep1 g NoDoc k ys = NoDoc
717 sep1 g (p `Union` q) k ys = sep1 g p k ys
719 (aboveNest q False k (reduceDoc (vcat ys)))
721 sep1 g Empty k ys = mkNest k (sepX g ys)
722 sep1 g (Nest n p) k ys = nest_ n (sep1 g p (k MINUS n) ys)
724 sep1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (reduceDoc (vcat ys)))
725 sep1 g (TextBeside s sl p) k ys = textBeside_ s sl (sepNB g p (k MINUS sl) ys)
727 -- Specification: sepNB p k ys = sep1 (text "" <> p) k ys
728 -- Called when we have already found some text in the first item
729 -- We have to eat up nests
731 sepNB g (Nest _ p) k ys = sepNB g p k ys
733 sepNB g Empty k ys = oneLiner (nilBeside g (reduceDoc rest))
735 nilAboveNest False k (reduceDoc (vcat ys))
738 | otherwise = hcat ys
740 sepNB g p k ys = sep1 g p k ys
743 *********************************************************
747 *********************************************************
756 -- fill (p1:p2:ps) = oneLiner p1 <#> nest (length p1)
757 -- (fill (oneLiner p2 : ps))
762 fill g (p:ps) = fill1 g (reduceDoc p) ILIT(0) ps
765 fill1 :: Bool -> RDoc -> INT -> [Doc] -> Doc
766 fill1 g NoDoc k ys = NoDoc
767 fill1 g (p `Union` q) k ys = fill1 g p k ys
769 (aboveNest q False k (fill g ys))
771 fill1 g Empty k ys = mkNest k (fill g ys)
772 fill1 g (Nest n p) k ys = nest_ n (fill1 g p (k MINUS n) ys)
774 fill1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (fill g ys))
775 fill1 g (TextBeside s sl p) k ys = textBeside_ s sl (fillNB g p (k MINUS sl) ys)
777 fillNB g (Nest _ p) k ys = fillNB g p k ys
778 fillNB g Empty k [] = Empty
779 fillNB g Empty k (y:ys) = nilBeside g (fill1 g (oneLiner (reduceDoc y)) k1 ys)
781 nilAboveNest False k (fill g (y:ys))
783 k1 | g = k MINUS ILIT(1)
786 fillNB g p k ys = fill1 g p k ys
790 *********************************************************
792 \subsection{Selecting the best layout}
794 *********************************************************
797 best :: Int -- Line length
798 -> Int -- Ribbon length
800 -> RDoc -- No unions in here!
802 best IBOX(w) IBOX(r) p
805 get :: INT -- (Remaining) width of line
809 get w (NilAbove p) = nilAbove_ (get w p)
810 get w (TextBeside s sl p) = textBeside_ s sl (get1 w sl p)
811 get w (Nest k p) = nest_ k (get (w MINUS k) p)
812 get w (p `Union` q) = nicest w r (get w p) (get w q)
814 get1 :: INT -- (Remaining) width of line
815 -> INT -- Amount of first line already eaten up
816 -> Doc -- This is an argument to TextBeside => eat Nests
817 -> Doc -- No unions in here!
819 get1 w sl Empty = Empty
820 get1 w sl NoDoc = NoDoc
821 get1 w sl (NilAbove p) = nilAbove_ (get (w MINUS sl) p)
822 get1 w sl (TextBeside t tl p) = textBeside_ t tl (get1 w (sl PLUS tl) p)
823 get1 w sl (Nest k p) = get1 w sl p
824 get1 w sl (p `Union` q) = nicest1 w r sl (get1 w sl p)
827 nicest w r p q = nicest1 w r ILIT(0) p q
828 nicest1 w r sl p q | fits ((w `minn` r) MINUS sl) p = p
831 fits :: INT -- Space available
833 -> Bool -- True if *first line* of Doc fits in space available
835 fits n p | n LT ILIT(0) = False
838 fits n (NilAbove _) = True
839 fits n (TextBeside _ sl p) = fits (n MINUS sl) p
841 minn x y | x LT y = x
845 @first@ and @nonEmptySet@ are similar to @nicest@ and @fits@, only simpler.
846 @first@ returns its first argument if it is non-empty, otherwise its second.
849 first p q | nonEmptySet p = p
852 nonEmptySet NoDoc = False
853 nonEmptySet (p `Union` q) = True
854 nonEmptySet Empty = True
855 nonEmptySet (NilAbove p) = True -- NoDoc always in first line
856 nonEmptySet (TextBeside _ _ p) = nonEmptySet p
857 nonEmptySet (Nest _ p) = nonEmptySet p
860 @oneLiner@ returns the one-line members of the given set of @Doc@s.
863 oneLiner :: Doc -> Doc
864 oneLiner NoDoc = NoDoc
865 oneLiner Empty = Empty
866 oneLiner (NilAbove p) = NoDoc
867 oneLiner (TextBeside s sl p) = textBeside_ s sl (oneLiner p)
868 oneLiner (Nest k p) = nest_ k (oneLiner p)
869 oneLiner (p `Union` q) = oneLiner p
874 *********************************************************
876 \subsection{Displaying the best layout}
878 *********************************************************
883 renderStyle Style{mode, lineLength, ribbonsPerLine} doc
884 = fullRender mode lineLength ribbonsPerLine doc ""
887 render doc = showDoc doc ""
888 showDoc doc rest = fullRender PageMode 100 1.5 string_txt rest doc
890 string_txt (Chr c) s = c:s
891 string_txt (Str s1) s2 = s1 ++ s2
892 string_txt (PStr s1) s2 = _UNPK_ s1 ++ s2
897 fullRender OneLineMode _ _ txt end doc
898 = lay (reduceDoc doc)
900 lay NoDoc = cant_fail
901 lay (Union p q) = (lay q) -- Second arg can't be NoDoc
902 lay (Nest k p) = lay p
904 lay (NilAbove p) = space_text `txt` lay p -- NoDoc always on first line
905 lay (TextBeside s sl p) = s `txt` lay p
907 fullRender LeftMode _ _ txt end doc
908 = lay (reduceDoc doc)
910 lay NoDoc = cant_fail
911 lay (Union p q) = lay (first p q)
912 lay (Nest k p) = lay p
914 lay (NilAbove p) = nl_text `txt` lay p -- NoDoc always on first line
915 lay (TextBeside s sl p) = s `txt` lay p
917 fullRender mode line_length ribbons_per_line txt end doc
918 = display mode line_length ribbon_length txt end best_doc
920 best_doc = best hacked_line_length ribbon_length (reduceDoc doc)
922 hacked_line_length, ribbon_length :: Int
923 ribbon_length = round (fromIntegral line_length / ribbons_per_line)
924 hacked_line_length = case mode of { ZigZagMode -> MAXINT; other -> line_length }
926 display mode IBOX(page_width) IBOX(ribbon_width) txt end doc
927 = case page_width MINUS ribbon_width of { gap_width ->
928 case gap_width DIV ILIT(2) of { shift ->
930 lay k (Nest k1 p) = lay (k PLUS k1) p
933 lay k (NilAbove p) = nl_text `txt` lay k p
935 lay k (TextBeside s sl p)
937 ZigZagMode | k GREQ gap_width
939 Str (multi_ch shift '/') `txt` (
941 lay1 (k MINUS shift) s sl p)))
945 Str (multi_ch shift '\\') `txt` (
947 lay1 (k PLUS shift) s sl p )))
949 other -> lay1 k s sl p
951 lay1 k s sl p = Str (indent k) `txt` (s `txt` lay2 (k PLUS sl) p)
953 lay2 k (NilAbove p) = nl_text `txt` lay k p
954 lay2 k (TextBeside s sl p) = s `txt` (lay2 (k PLUS sl) p)
955 lay2 k (Nest _ p) = lay2 k p
961 cant_fail = error "easy_display: NoDoc"
963 indent n | n GREQ ILIT(8) = '\t' : indent (n MINUS ILIT(8))
964 | otherwise = spaces n
966 multi_ch ILIT(0) ch = ""
967 multi_ch n ch = ch : multi_ch (n MINUS ILIT(1)) ch
970 spaces n = ' ' : spaces (n MINUS ILIT(1))
974 pprCols = (100 :: Int) -- could make configurable
976 printDoc :: Mode -> Handle -> Doc -> IO ()
977 printDoc mode hdl doc
978 = fullRender mode pprCols 1.5 put done doc
980 put (Chr c) next = hPutChar hdl c >> next
981 put (Str s) next = hPutStr hdl s >> next
982 put (PStr s) next = hPutFS hdl s >> next
984 done = hPutChar hdl '\n'