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 (FastString) 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 $$, and anywhere in the argument list for
85 sep, hcat, hsep, vcat, fcat etc.
87 It is Really Useful in practice.
89 2. There is a paragraph-fill combinator, fsep, that's much like sep,
90 only it keeps fitting things on one line until it can't fit any more.
92 3. Some random useful extra combinators are provided.
93 <+> puts its arguments beside each other with a space between them,
94 unless either argument is empty in which case it returns the other
97 hcat is a list version of <>
98 hsep is a list version of <+>
99 vcat is a list version of $$
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
156 -- The above warning supression flag is a temporary kludge.
157 -- While working on this module you are encouraged to remove it and fix
158 -- any warnings in the module. See
159 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
164 Mode(..), TextDetails(..),
166 empty, isEmpty, nest,
168 text, char, ftext, ptext,
169 int, integer, float, double, rational,
170 parens, brackets, braces, quotes, doubleQuotes,
171 semi, comma, colon, space, equals,
172 lparen, rparen, lbrack, rbrack, lbrace, rbrace, cparen,
174 (<>), (<+>), hcat, hsep,
181 -- renderStyle, -- Haskell 1.3 only
182 render, fullRender, printDoc, showDocWith
185 #include "HsVersions.h"
191 import Numeric (fromRat)
193 --import Foreign.Ptr (castPtr)
195 #if defined(__GLASGOW_HASKELL__)
197 import GHC.Base ( unpackCString# )
198 import GHC.Ptr ( Ptr(..) )
201 -- Don't import Util( assertPanic ) because it makes a loop in the module structure
211 -- Disable ASSERT checks; they are expensive!
212 #define LOCAL_ASSERT(x)
217 *********************************************************
219 \subsection{The interface}
221 *********************************************************
223 The primitive @Doc@ values
227 isEmpty :: Doc -> Bool
228 text :: String -> Doc
231 semi, comma, colon, space, equals :: Doc
232 lparen, rparen, lbrack, rbrack, lbrace, rbrace :: Doc
234 parens, brackets, braces :: Doc -> Doc
235 quotes, doubleQuotes :: Doc -> Doc
238 integer :: Integer -> Doc
239 float :: Float -> Doc
240 double :: Double -> Doc
241 rational :: Rational -> Doc
244 Combining @Doc@ values
247 (<>) :: Doc -> Doc -> Doc -- Beside
248 hcat :: [Doc] -> Doc -- List version of <>
249 (<+>) :: Doc -> Doc -> Doc -- Beside, separated by space
250 hsep :: [Doc] -> Doc -- List version of <+>
252 ($$) :: Doc -> Doc -> Doc -- Above; if there is no
253 -- overlap it "dovetails" the two
254 vcat :: [Doc] -> Doc -- List version of $$
256 cat :: [Doc] -> Doc -- Either hcat or vcat
257 sep :: [Doc] -> Doc -- Either hsep or vcat
258 fcat :: [Doc] -> Doc -- ``Paragraph fill'' version of cat
259 fsep :: [Doc] -> Doc -- ``Paragraph fill'' version of sep
261 nest :: Int -> Doc -> Doc -- Nested
267 hang :: Doc -> Int -> Doc -> Doc
268 punctuate :: Doc -> [Doc] -> [Doc] -- punctuate p [d1, ... dn] = [d1 <> p, d2 <> p, ... dn-1 <> p, dn]
271 Displaying @Doc@ values.
274 instance Show Doc where
275 showsPrec prec doc cont = showDoc doc cont
277 render :: Doc -> String -- Uses default style
279 -> Int -- Line length
280 -> Float -- Ribbons per line
281 -> (TextDetails -> a -> a) -- What to do with text
282 -> a -- What to do at the end
286 {- When we start using 1.3
287 renderStyle :: Style -> Doc -> String
288 data Style = Style { lineLength :: Int, -- In chars
289 ribbonsPerLine :: Float, -- Ratio of ribbon length to line length
292 style :: Style -- The default style
293 style = Style { lineLength = 100, ribbonsPerLine = 2.5, mode = PageMode }
296 data Mode = PageMode -- Normal
297 | ZigZagMode -- With zig-zag cuts
298 | LeftMode -- No indentation, infinitely long lines
299 | OneLineMode -- All on one line
304 *********************************************************
306 \subsection{The @Doc@ calculus}
308 *********************************************************
310 The @Doc@ combinators satisfy the following laws:
314 <a1> (x $$ y) $$ z = x $$ (y $$ z)
322 <b1> (x <> y) <> z = x <> (y <> z)
323 <b2> empty <> x = empty
330 <t1> text s <> text t = text (s++t)
331 <t2> text "" <> x = x, if x non-empty
336 <n2> nest k (nest k' x) = nest (k+k') x
337 <n3> nest k (x <> y) = nest k z <> nest k y
338 <n4> nest k (x $$ y) = nest k x $$ nest k y
339 <n5> nest k empty = empty
340 <n6> x <> nest k y = x <> y, if x non-empty
342 ** Note the side condition on <n6>! It is this that
343 ** makes it OK for empty to be a left unit for <>.
347 <m1> (text s <> x) $$ y = text s <> ((text "" <> x)) $$
350 <m2> (x $$ y) <> z = x $$ (y <> z)
354 Laws for list versions
355 ~~~~~~~~~~~~~~~~~~~~~~
356 <l1> sep (ps++[empty]++qs) = sep (ps ++ qs)
357 ...ditto hsep, hcat, vcat, fill...
359 <l2> nest k (sep ps) = sep (map (nest k) ps)
360 ...ditto hsep, hcat, vcat, fill...
364 <o1> oneLiner (nest k p) = nest k (oneLiner p)
365 <o2> oneLiner (x <> y) = oneLiner x <> oneLiner y
369 You might think that the following verion of <m1> would
372 <3 NO> (text s <> x) $$ y = text s <> ((empty <> x)) $$
375 But it doesn't work, for if x=empty, we would have
377 text s $$ y = text s <> (empty $$ nest (-length s) y)
378 = text s <> nest (-length s) y
383 *********************************************************
385 \subsection{Simple derived definitions}
387 *********************************************************
402 int n = text (show n)
403 integer n = text (show n)
404 float n = text (show n)
405 double n = text (show n)
406 rational n = text (show (fromRat n :: Double))
407 --rational n = text (show (fromRationalX n)) -- _showRational 30 n)
409 quotes p = char '`' <> p <> char '\''
410 doubleQuotes p = char '"' <> p <> char '"'
411 parens p = char '(' <> p <> char ')'
412 brackets p = char '[' <> p <> char ']'
413 braces p = char '{' <> p <> char '}'
418 hcat = foldr (<>) empty
419 hsep = foldr (<+>) empty
420 vcat = foldr ($$) empty
422 hang d1 n d2 = sep [d1, nest n d2]
425 punctuate p (d:ds) = go d ds
428 go d (e:es) = (d <> p) : go e es
432 *********************************************************
434 \subsection{The @Doc@ data type}
436 *********************************************************
438 A @Doc@ represents a {\em set} of layouts. A @Doc@ with
439 no occurrences of @Union@ or @NoDoc@ represents just one layout.
443 | NilAbove Doc -- text "" $$ x
444 | TextBeside !TextDetails FastInt Doc -- text s <> x
445 | Nest FastInt Doc -- nest k x
446 | Union Doc Doc -- ul `union` ur
447 | NoDoc -- The empty set of documents
448 | Beside Doc Bool Doc -- True <=> space between
449 | Above Doc Bool Doc -- True <=> never overlap
451 type RDoc = Doc -- RDoc is a "reduced Doc", guaranteed not to have a top-level Above or Beside
454 reduceDoc :: Doc -> RDoc
455 reduceDoc (Beside p g q) = beside p g (reduceDoc q)
456 reduceDoc (Above p g q) = above p g (reduceDoc q)
460 data TextDetails = Chr {-#UNPACK#-}!Char
462 | PStr FastString -- a hashed string
463 | LStr {-#UNPACK#-}!LitString FastInt -- a '\0'-terminated
470 Here are the invariants:
473 The argument of @NilAbove@ is never @Empty@. Therefore
474 a @NilAbove@ occupies at least two lines.
477 The arugment of @TextBeside@ is never @Nest@.
480 The layouts of the two arguments of @Union@ both flatten to the same string.
483 The arguments of @Union@ are either @TextBeside@, or @NilAbove@.
486 The right argument of a union cannot be equivalent to the empty set (@NoDoc@).
487 If the left argument of a union is equivalent to the empty set (@NoDoc@),
488 then the @NoDoc@ appears in the first line.
491 An empty document is always represented by @Empty@.
492 It can't be hidden inside a @Nest@, or a @Union@ of two @Empty@s.
495 The first line of every layout in the left argument of @Union@
496 is longer than the first line of any layout in the right argument.
497 (1) ensures that the left argument has a first line. In view of (3),
498 this invariant means that the right argument must have at least two
503 -- Arg of a NilAbove is always an RDoc
504 nilAbove_ p = LOCAL_ASSERT( ok p ) NilAbove p
509 -- Arg of a TextBeside is always an RDoc
510 textBeside_ s sl p = TextBeside s sl (LOCAL_ASSERT( ok p ) p)
512 ok (Nest _ _) = False
515 -- Arg of Nest is always an RDoc
516 nest_ k p = Nest k (LOCAL_ASSERT( ok p ) p)
521 -- Args of union are always RDocs
522 union_ p q = Union (LOCAL_ASSERT( ok p ) p) (LOCAL_ASSERT( ok q ) q)
524 ok (TextBeside _ _ _) = True
525 ok (NilAbove _) = True
526 ok (Union _ _) = True
531 Notice the difference between
532 * NoDoc (no documents)
533 * Empty (one empty document; no height and no width)
534 * text "" (a document containing the empty string;
535 one line high, but has no width)
539 *********************************************************
541 \subsection{@empty@, @text@, @nest@, @union@}
543 *********************************************************
551 char c = textBeside_ (Chr c) (_ILIT(1)) Empty
552 text s = case iUnbox (length s) of {sl -> textBeside_ (Str s) sl Empty}
553 ftext s = case iUnbox (lengthFS s) of {sl -> textBeside_ (PStr s) sl Empty}
554 ptext s_= case iUnbox (strLength s) of {sl -> textBeside_ (LStr s sl) sl Empty}
555 where s = {-castPtr-} s_
557 #if defined(__GLASGOW_HASKELL__)
558 -- RULE that turns (text "abc") into (ptext (A# "abc"#)) to avoid the
559 -- intermediate packing/unpacking of the string.
561 "text/str" forall a. text (unpackCString# a) = ptext (Ptr a)
565 nest k p = mkNest (iUnbox k) (reduceDoc p) -- Externally callable version
567 -- mkNest checks for Nest's invariant that it doesn't have an Empty inside it
568 mkNest k (Nest k1 p) = mkNest (k +# k1) p
569 mkNest k NoDoc = NoDoc
570 mkNest k Empty = Empty
571 mkNest k p | k ==# _ILIT(0) = p -- Worth a try!
572 mkNest k p = nest_ k p
574 -- mkUnion checks for an empty document
575 mkUnion Empty q = Empty
576 mkUnion p q = p `union_` q
579 *********************************************************
581 \subsection{Vertical composition @$$@}
583 *********************************************************
587 p $$ q = Above p False q
588 p $+$ q = Above p True q
590 above :: Doc -> Bool -> RDoc -> RDoc
591 above (Above p g1 q1) g2 q2 = above p g1 (above q1 g2 q2)
592 above p@(Beside _ _ _) g q = aboveNest (reduceDoc p) g (_ILIT(0)) (reduceDoc q)
593 above p g q = aboveNest p g (_ILIT(0)) (reduceDoc q)
595 aboveNest :: RDoc -> Bool -> FastInt -> RDoc -> RDoc
596 -- Specfication: aboveNest p g k q = p $g$ (nest k q)
598 aboveNest NoDoc g k q = NoDoc
599 aboveNest (p1 `Union` p2) g k q = aboveNest p1 g k q `union_`
602 aboveNest Empty g k q = mkNest k q
603 aboveNest (Nest k1 p) g k q = nest_ k1 (aboveNest p g (k -# k1) q)
604 -- p can't be Empty, so no need for mkNest
606 aboveNest (NilAbove p) g k q = nilAbove_ (aboveNest p g k q)
607 aboveNest (TextBeside s sl p) g k q = textBeside_ s sl rest
611 Empty -> nilAboveNest g k1 q
612 other -> aboveNest p g k1 q
616 nilAboveNest :: Bool -> FastInt -> RDoc -> RDoc
617 -- Specification: text s <> nilaboveNest g k q
618 -- = text s <> (text "" $g$ nest k q)
620 nilAboveNest g k Empty = Empty -- Here's why the "text s <>" is in the spec!
621 nilAboveNest g k (Nest k1 q) = nilAboveNest g (k +# k1) q
623 nilAboveNest g k q | (not g) && (k ># _ILIT(0)) -- No newline if no overlap
624 = textBeside_ (Str (spaces k)) k q
625 | otherwise -- Put them really above
626 = nilAbove_ (mkNest k q)
630 *********************************************************
632 \subsection{Horizontal composition @<>@}
634 *********************************************************
637 p <> q = Beside p False q
638 p <+> q = Beside p True q
640 beside :: Doc -> Bool -> RDoc -> RDoc
641 -- Specification: beside g p q = p <g> q
643 beside NoDoc g q = NoDoc
644 beside (p1 `Union` p2) g q = (beside p1 g q) `union_` (beside p2 g q)
646 beside (Nest k p) g q = nest_ k $! beside p g q -- p non-empty
647 beside p@(Beside p1 g1 q1) g2 q2
648 {- (A `op1` B) `op2` C == A `op1` (B `op2` C) iff op1 == op2
649 [ && (op1 == <> || op1 == <+>) ] -}
650 | g1 == g2 = beside p1 g1 $! beside q1 g2 q2
651 | otherwise = beside (reduceDoc p) g2 q2
652 beside p@(Above _ _ _) g q = let d = reduceDoc p in d `seq` beside d g q
653 beside (NilAbove p) g q = nilAbove_ $! beside p g q
654 beside (TextBeside s sl p) g q = textBeside_ s sl $! rest
657 Empty -> nilBeside g q
658 other -> beside p g q
662 nilBeside :: Bool -> RDoc -> RDoc
663 -- Specification: text "" <> nilBeside g p
666 nilBeside g Empty = Empty -- Hence the text "" in the spec
667 nilBeside g (Nest _ p) = nilBeside g p
668 nilBeside g p | g = textBeside_ space_text (_ILIT(1)) p
672 *********************************************************
674 \subsection{Separate, @sep@, Hughes version}
676 *********************************************************
679 -- Specification: sep ps = oneLiner (hsep ps)
683 sep = sepX True -- Separate with spaces
684 cat = sepX False -- Don't
687 sepX x (p:ps) = sep1 x (reduceDoc p) (_ILIT(0)) ps
690 -- Specification: sep1 g k ys = sep (x : map (nest k) ys)
691 -- = oneLiner (x <g> nest k (hsep ys))
692 -- `union` x $$ nest k (vcat ys)
694 sep1 :: Bool -> RDoc -> FastInt -> [Doc] -> RDoc
695 sep1 g NoDoc k ys = NoDoc
696 sep1 g (p `Union` q) k ys = sep1 g p k ys
698 (aboveNest q False k (reduceDoc (vcat ys)))
700 sep1 g Empty k ys = mkNest k (sepX g ys)
701 sep1 g (Nest n p) k ys = nest_ n (sep1 g p (k -# n) ys)
703 sep1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (reduceDoc (vcat ys)))
704 sep1 g (TextBeside s sl p) k ys = textBeside_ s sl (sepNB g p (k -# sl) ys)
706 -- Specification: sepNB p k ys = sep1 (text "" <> p) k ys
707 -- Called when we have already found some text in the first item
708 -- We have to eat up nests
710 sepNB g (Nest _ p) k ys = sepNB g p k ys
712 sepNB g Empty k ys = oneLiner (nilBeside g (reduceDoc rest))
714 nilAboveNest False k (reduceDoc (vcat ys))
717 | otherwise = hcat ys
719 sepNB g p k ys = sep1 g p k ys
722 *********************************************************
726 *********************************************************
735 -- fill (p1:p2:ps) = oneLiner p1 <#> nest (length p1)
736 -- (fill (oneLiner p2 : ps))
741 fill g (p:ps) = fill1 g (reduceDoc p) (_ILIT(0)) ps
744 fill1 :: Bool -> RDoc -> FastInt -> [Doc] -> Doc
745 fill1 g NoDoc k ys = NoDoc
746 fill1 g (p `Union` q) k ys = fill1 g p k ys
748 (aboveNest q False k (fill g ys))
750 fill1 g Empty k ys = mkNest k (fill g ys)
751 fill1 g (Nest n p) k ys = nest_ n (fill1 g p (k -# n) ys)
753 fill1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (fill g ys))
754 fill1 g (TextBeside s sl p) k ys = textBeside_ s sl (fillNB g p (k -# sl) ys)
756 fillNB g (Nest _ p) k ys = fillNB g p k ys
757 fillNB g Empty k [] = Empty
758 fillNB g Empty k (y:ys) = nilBeside g (fill1 g (oneLiner (reduceDoc y)) k1 ys)
760 nilAboveNest False k (fill g (y:ys))
762 k1 | g = k -# _ILIT(1)
765 fillNB g p k ys = fill1 g p k ys
769 *********************************************************
771 \subsection{Selecting the best layout}
773 *********************************************************
776 best :: Int -- Line length
777 -> Int -- Ribbon length
779 -> RDoc -- No unions in here!
785 get :: FastInt -- (Remaining) width of line
789 get w (NilAbove p) = nilAbove_ (get w p)
790 get w (TextBeside s sl p) = textBeside_ s sl (get1 w sl p)
791 get w (Nest k p) = nest_ k (get (w -# k) p)
792 get w (p `Union` q) = nicest w r (get w p) (get w q)
794 get1 :: FastInt -- (Remaining) width of line
795 -> FastInt -- Amount of first line already eaten up
796 -> Doc -- This is an argument to TextBeside => eat Nests
797 -> Doc -- No unions in here!
799 get1 w sl Empty = Empty
800 get1 w sl NoDoc = NoDoc
801 get1 w sl (NilAbove p) = nilAbove_ (get (w -# sl) p)
802 get1 w sl (TextBeside t tl p) = textBeside_ t tl (get1 w (sl +# tl) p)
803 get1 w sl (Nest k p) = get1 w sl p
804 get1 w sl (p `Union` q) = nicest1 w r sl (get1 w sl p)
807 nicest w r p q = nicest1 w r (_ILIT(0)) p q
808 nicest1 w r sl p q | fits ((w `minFastInt` r) -# sl) p = p
811 fits :: FastInt -- Space available
813 -> Bool -- True if *first line* of Doc fits in space available
815 fits n p | n <# _ILIT(0) = False
818 fits n (NilAbove _) = True
819 fits n (TextBeside _ sl p) = fits (n -# sl) p
822 @first@ and @nonEmptySet@ are similar to @nicest@ and @fits@, only simpler.
823 @first@ returns its first argument if it is non-empty, otherwise its second.
826 first p q | nonEmptySet p = p
829 nonEmptySet NoDoc = False
830 nonEmptySet (p `Union` q) = True
831 nonEmptySet Empty = True
832 nonEmptySet (NilAbove p) = True -- NoDoc always in first line
833 nonEmptySet (TextBeside _ _ p) = nonEmptySet p
834 nonEmptySet (Nest _ p) = nonEmptySet p
837 @oneLiner@ returns the one-line members of the given set of @Doc@s.
840 oneLiner :: Doc -> Doc
841 oneLiner NoDoc = NoDoc
842 oneLiner Empty = Empty
843 oneLiner (NilAbove p) = NoDoc
844 oneLiner (TextBeside s sl p) = textBeside_ s sl (oneLiner p)
845 oneLiner (Nest k p) = nest_ k (oneLiner p)
846 oneLiner (p `Union` q) = oneLiner p
851 *********************************************************
853 \subsection{Displaying the best layout}
855 *********************************************************
860 renderStyle Style{mode, lineLength, ribbonsPerLine} doc
861 = fullRender mode lineLength ribbonsPerLine doc ""
864 render doc = showDocWith PageMode doc
865 showDoc doc rest = showDocWithAppend PageMode doc rest
867 showDocWithAppend :: Mode -> Doc -> String -> String
868 showDocWithAppend mode doc rest = fullRender mode 100 1.5 string_txt rest doc
870 showDocWith :: Mode -> Doc -> String
871 showDocWith mode doc = showDocWithAppend mode doc ""
873 string_txt (Chr c) s = c:s
874 string_txt (Str s1) s2 = s1 ++ s2
875 string_txt (PStr s1) s2 = unpackFS s1 ++ s2
876 string_txt (LStr s1 _) s2 = unpackLitString s1 ++ s2
881 fullRender OneLineMode _ _ txt end doc
882 = lay (reduceDoc doc)
884 lay NoDoc = cant_fail
885 lay (Union p q) = (lay q) -- Second arg can't be NoDoc
886 lay (Nest k p) = lay p
888 lay (NilAbove p) = space_text `txt` lay p -- NoDoc always on
890 lay (TextBeside s sl p) = s `txt` lay p
892 fullRender LeftMode _ _ txt end doc
893 = lay (reduceDoc doc)
895 lay NoDoc = cant_fail
896 lay (Union p q) = lay (first p q)
897 lay (Nest k p) = lay p
899 lay (NilAbove p) = nl_text `txt` lay p -- NoDoc always on first line
900 lay (TextBeside s sl p) = s `txt` lay p
902 fullRender mode line_length ribbons_per_line txt end doc
903 = display mode line_length ribbon_length txt end best_doc
905 best_doc = best hacked_line_length ribbon_length (reduceDoc doc)
907 hacked_line_length, ribbon_length :: Int
908 ribbon_length = round (fromIntegral line_length / ribbons_per_line)
909 hacked_line_length = case mode of { ZigZagMode -> maxBound; other -> line_length }
911 display mode page_width ribbon_width txt end doc
912 = case (iUnbox page_width) -# (iUnbox ribbon_width) of { gap_width ->
913 case gap_width `quotFastInt` _ILIT(2) of { shift ->
915 lay k (Nest k1 p) = lay (k +# k1) p
918 lay k (NilAbove p) = nl_text `txt` lay k p
920 lay k (TextBeside s sl p)
922 ZigZagMode | k >=# gap_width
924 Str (multi_ch shift '/') `txt` (
926 lay1 (k -# shift) s sl p)))
930 Str (multi_ch shift '\\') `txt` (
932 lay1 (k +# shift) s sl p )))
934 other -> lay1 k s sl p
936 lay1 k s sl p = indent k (s `txt` lay2 (k +# sl) p)
938 lay2 k (NilAbove p) = nl_text `txt` lay k p
939 lay2 k (TextBeside s sl p) = s `txt` (lay2 (k +# sl) p)
940 lay2 k (Nest _ p) = lay2 k p
943 -- optimise long indentations using LitString chunks of 8 spaces
944 indent n r | n >=# _ILIT(8) = LStr SLIT(" ") (_ILIT(8)) `txt`
945 indent (n -# _ILIT(8)) r
946 | otherwise = Str (spaces n) `txt` r
951 cant_fail = error "easy_display: NoDoc"
953 multi_ch n ch | n <=# _ILIT(0) = ""
954 | otherwise = ch : multi_ch (n -# _ILIT(1)) ch
956 spaces n | n <=# _ILIT(0) = ""
957 | otherwise = ' ' : spaces (n -# _ILIT(1))
962 pprCols = (120 :: Int) -- could make configurable
964 printDoc :: Mode -> Handle -> Doc -> IO ()
965 printDoc LeftMode hdl doc
966 = do { printLeftRender hdl doc; hFlush hdl }
967 printDoc mode hdl doc
968 = do { fullRender mode pprCols 1.5 put done doc ;
971 put (Chr c) next = hPutChar hdl c >> next
972 put (Str s) next = hPutStr hdl s >> next
973 put (PStr s) next = hPutFS hdl s >> next
974 put (LStr s l) next = hPutLitString hdl s l >> next
976 done = hPutChar hdl '\n'
978 -- some versions of hPutBuf will barf if the length is zero
979 hPutLitString handle a l = if l ==# _ILIT(0)
981 else hPutBuf handle a (iBox l)
983 -- Printing output in LeftMode is performance critical: it's used when
984 -- dumping C and assembly output, so we allow ourselves a few dirty
987 -- (1) we specialise fullRender for LeftMode with IO output.
989 -- (2) we add a layer of buffering on top of Handles. Handles
990 -- don't perform well with lots of hPutChars, which is mostly
991 -- what we're doing here, because Handles have to be thread-safe
992 -- and async exception-safe. We only have a single thread and don't
993 -- care about exceptions, so we add a layer of fast buffering
994 -- over the Handle interface.
996 -- (3) a few hacks in layLeft below to convince GHC to generate the right
999 printLeftRender :: Handle -> Doc -> IO ()
1000 printLeftRender hdl doc = do
1001 b <- newBufHandle hdl
1002 layLeft b (reduceDoc doc)
1005 -- HACK ALERT! the "return () >>" below convinces GHC to eta-expand
1006 -- this function with the IO state lambda. Otherwise we end up with
1007 -- closures in all the case branches.
1008 layLeft b _ | b `seq` False = undefined -- make it strict in b
1009 layLeft b NoDoc = cant_fail
1010 layLeft b (Union p q) = return () >> layLeft b (first p q)
1011 layLeft b (Nest k p) = return () >> layLeft b p
1012 layLeft b Empty = bPutChar b '\n'
1013 layLeft b (NilAbove p) = bPutChar b '\n' >> layLeft b p
1014 layLeft b (TextBeside s sl p) = put b s >> layLeft b p
1016 put b _ | b `seq` False = undefined
1017 put b (Chr c) = bPutChar b c
1018 put b (Str s) = bPutStr b s
1019 put b (PStr s) = bPutFS b s
1020 put b (LStr s l) = bPutLitString b s l