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
157 Mode(..), TextDetails(..),
159 empty, isEmpty, nest,
161 text, char, ftext, ptext,
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, cparen,
167 (<>), (<+>), hcat, hsep,
174 -- renderStyle, -- Haskell 1.3 only
175 render, fullRender, printDoc, showDocWith
183 import Numeric (fromRat)
185 --import Foreign.Ptr (castPtr)
187 #if defined(__GLASGOW_HASKELL__)
189 import GHC.Base ( unpackCString# )
190 import GHC.Exts ( Int# )
191 import GHC.Ptr ( Ptr(..) )
194 -- Don't import Util( assertPanic ) because it makes a loop in the module structure
204 -- Disable ASSERT checks; they are expensive!
205 #define LOCAL_ASSERT(x)
210 *********************************************************
212 \subsection{The interface}
214 *********************************************************
216 The primitive @Doc@ values
220 isEmpty :: Doc -> Bool
221 text :: String -> Doc
224 semi, comma, colon, space, equals :: Doc
225 lparen, rparen, lbrack, rbrack, lbrace, rbrace :: Doc
227 parens, brackets, braces :: Doc -> Doc
228 quotes, doubleQuotes :: Doc -> Doc
231 integer :: Integer -> Doc
232 float :: Float -> Doc
233 double :: Double -> Doc
234 rational :: Rational -> Doc
237 Combining @Doc@ values
240 (<>) :: Doc -> Doc -> Doc -- Beside
241 hcat :: [Doc] -> Doc -- List version of <>
242 (<+>) :: Doc -> Doc -> Doc -- Beside, separated by space
243 hsep :: [Doc] -> Doc -- List version of <+>
245 ($$) :: Doc -> Doc -> Doc -- Above; if there is no
246 -- overlap it "dovetails" the two
247 vcat :: [Doc] -> Doc -- List version of $$
249 cat :: [Doc] -> Doc -- Either hcat or vcat
250 sep :: [Doc] -> Doc -- Either hsep or vcat
251 fcat :: [Doc] -> Doc -- ``Paragraph fill'' version of cat
252 fsep :: [Doc] -> Doc -- ``Paragraph fill'' version of sep
254 nest :: Int -> Doc -> Doc -- Nested
260 hang :: Doc -> Int -> Doc -> Doc
261 punctuate :: Doc -> [Doc] -> [Doc] -- punctuate p [d1, ... dn] = [d1 <> p, d2 <> p, ... dn-1 <> p, dn]
264 Displaying @Doc@ values.
267 instance Show Doc where
268 showsPrec _ doc cont = showDoc doc cont
270 render :: Doc -> String -- Uses default style
272 -> Int -- Line length
273 -> Float -- Ribbons per line
274 -> (TextDetails -> a -> a) -- What to do with text
275 -> a -- What to do at the end
279 {- When we start using 1.3
280 renderStyle :: Style -> Doc -> String
281 data Style = Style { lineLength :: Int, -- In chars
282 ribbonsPerLine :: Float, -- Ratio of ribbon length to line length
285 style :: Style -- The default style
286 style = Style { lineLength = 100, ribbonsPerLine = 2.5, mode = PageMode }
289 data Mode = PageMode -- Normal
290 | ZigZagMode -- With zig-zag cuts
291 | LeftMode -- No indentation, infinitely long lines
292 | OneLineMode -- All on one line
297 *********************************************************
299 \subsection{The @Doc@ calculus}
301 *********************************************************
303 The @Doc@ combinators satisfy the following laws:
307 <a1> (x $$ y) $$ z = x $$ (y $$ z)
315 <b1> (x <> y) <> z = x <> (y <> z)
316 <b2> empty <> x = empty
323 <t1> text s <> text t = text (s++t)
324 <t2> text "" <> x = x, if x non-empty
329 <n2> nest k (nest k' x) = nest (k+k') x
330 <n3> nest k (x <> y) = nest k z <> nest k y
331 <n4> nest k (x $$ y) = nest k x $$ nest k y
332 <n5> nest k empty = empty
333 <n6> x <> nest k y = x <> y, if x non-empty
335 ** Note the side condition on <n6>! It is this that
336 ** makes it OK for empty to be a left unit for <>.
340 <m1> (text s <> x) $$ y = text s <> ((text "" <> x)) $$
343 <m2> (x $$ y) <> z = x $$ (y <> z)
347 Laws for list versions
348 ~~~~~~~~~~~~~~~~~~~~~~
349 <l1> sep (ps++[empty]++qs) = sep (ps ++ qs)
350 ...ditto hsep, hcat, vcat, fill...
352 <l2> nest k (sep ps) = sep (map (nest k) ps)
353 ...ditto hsep, hcat, vcat, fill...
357 <o1> oneLiner (nest k p) = nest k (oneLiner p)
358 <o2> oneLiner (x <> y) = oneLiner x <> oneLiner y
362 You might think that the following verion of <m1> would
365 <3 NO> (text s <> x) $$ y = text s <> ((empty <> x)) $$
368 But it doesn't work, for if x=empty, we would have
370 text s $$ y = text s <> (empty $$ nest (-length s) y)
371 = text s <> nest (-length s) y
376 *********************************************************
378 \subsection{Simple derived definitions}
380 *********************************************************
395 int n = text (show n)
396 integer n = text (show n)
397 float n = text (show n)
398 double n = text (show n)
399 rational n = text (show (fromRat n :: Double))
400 --rational n = text (show (fromRationalX n)) -- _showRational 30 n)
402 quotes p = char '`' <> p <> char '\''
403 doubleQuotes p = char '"' <> p <> char '"'
404 parens p = char '(' <> p <> char ')'
405 brackets p = char '[' <> p <> char ']'
406 braces p = char '{' <> p <> char '}'
408 cparen :: Bool -> Doc -> Doc
412 hcat = foldr (<>) empty
413 hsep = foldr (<+>) empty
414 vcat = foldr ($$) empty
416 hang d1 n d2 = sep [d1, nest n d2]
419 punctuate p (d:ds) = go d ds
422 go d (e:es) = (d <> p) : go e es
426 *********************************************************
428 \subsection{The @Doc@ data type}
430 *********************************************************
432 A @Doc@ represents a {\em set} of layouts. A @Doc@ with
433 no occurrences of @Union@ or @NoDoc@ represents just one layout.
437 | NilAbove Doc -- text "" $$ x
438 | TextBeside !TextDetails FastInt Doc -- text s <> x
439 | Nest FastInt Doc -- nest k x
440 | Union Doc Doc -- ul `union` ur
441 | NoDoc -- The empty set of documents
442 | Beside Doc Bool Doc -- True <=> space between
443 | Above Doc Bool Doc -- True <=> never overlap
445 type RDoc = Doc -- RDoc is a "reduced Doc", guaranteed not to have a top-level Above or Beside
448 reduceDoc :: Doc -> RDoc
449 reduceDoc (Beside p g q) = beside p g (reduceDoc q)
450 reduceDoc (Above p g q) = above p g (reduceDoc q)
454 data TextDetails = Chr {-#UNPACK#-}!Char
456 | PStr FastString -- a hashed string
457 | LStr {-#UNPACK#-}!LitString FastInt -- a '\0'-terminated
460 space_text :: TextDetails
462 nl_text :: TextDetails
466 Here are the invariants:
469 The argument of @NilAbove@ is never @Empty@. Therefore
470 a @NilAbove@ occupies at least two lines.
473 The arugment of @TextBeside@ is never @Nest@.
476 The layouts of the two arguments of @Union@ both flatten to the same string.
479 The arguments of @Union@ are either @TextBeside@, or @NilAbove@.
482 The right argument of a union cannot be equivalent to the empty set (@NoDoc@).
483 If the left argument of a union is equivalent to the empty set (@NoDoc@),
484 then the @NoDoc@ appears in the first line.
487 An empty document is always represented by @Empty@.
488 It can't be hidden inside a @Nest@, or a @Union@ of two @Empty@s.
491 The first line of every layout in the left argument of @Union@
492 is longer than the first line of any layout in the right argument.
493 (1) ensures that the left argument has a first line. In view of (3),
494 this invariant means that the right argument must have at least two
499 -- Arg of a NilAbove is always an RDoc
500 nilAbove_ :: Doc -> Doc
501 nilAbove_ p = LOCAL_ASSERT( _ok p ) NilAbove p
506 -- Arg of a TextBeside is always an RDoc
507 textBeside_ :: TextDetails -> FastInt -> Doc -> Doc
508 textBeside_ s sl p = TextBeside s sl (LOCAL_ASSERT( _ok p ) p)
510 _ok (Nest _ _) = False
513 -- Arg of Nest is always an RDoc
514 nest_ :: FastInt -> Doc -> Doc
515 nest_ k p = Nest k (LOCAL_ASSERT( _ok p ) p)
520 -- Args of union are always RDocs
521 union_ :: Doc -> Doc -> Doc
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 :: FastString -> Doc
554 ftext s = case iUnbox (lengthFS s) of {sl -> textBeside_ (PStr s) sl Empty}
555 ptext :: LitString -> Doc
556 ptext s_= case iUnbox (strLength s) of {sl -> textBeside_ (LStr s sl) sl Empty}
557 where s = {-castPtr-} s_
559 #if defined(__GLASGOW_HASKELL__)
560 -- RULE that turns (text "abc") into (ptext (A# "abc"#)) to avoid the
561 -- intermediate packing/unpacking of the string.
563 "text/str" forall a. text (unpackCString# a) = ptext (Ptr a)
567 nest k p = mkNest (iUnbox k) (reduceDoc p) -- Externally callable version
569 -- mkNest checks for Nest's invariant that it doesn't have an Empty inside it
570 mkNest :: Int# -> Doc -> Doc
571 mkNest k (Nest k1 p) = mkNest (k +# k1) p
572 mkNest _ NoDoc = NoDoc
573 mkNest _ Empty = Empty
574 mkNest k p | k ==# _ILIT(0) = p -- Worth a try!
575 mkNest k p = nest_ k p
577 -- mkUnion checks for an empty document
578 mkUnion :: Doc -> Doc -> Doc
579 mkUnion Empty _ = Empty
580 mkUnion p q = p `union_` q
583 *********************************************************
585 \subsection{Vertical composition @$$@}
587 *********************************************************
591 p $$ q = Above p False q
592 ($+$) :: Doc -> Doc -> Doc
593 p $+$ q = Above p True q
595 above :: Doc -> Bool -> RDoc -> RDoc
596 above (Above p g1 q1) g2 q2 = above p g1 (above q1 g2 q2)
597 above p@(Beside _ _ _) g q = aboveNest (reduceDoc p) g (_ILIT(0)) (reduceDoc q)
598 above p g q = aboveNest p g (_ILIT(0)) (reduceDoc q)
600 aboveNest :: RDoc -> Bool -> FastInt -> RDoc -> RDoc
601 -- Specfication: aboveNest p g k q = p $g$ (nest k q)
603 aboveNest NoDoc _ _ _ = NoDoc
604 aboveNest (p1 `Union` p2) g k q = aboveNest p1 g k q `union_`
607 aboveNest Empty _ k q = mkNest k q
608 aboveNest (Nest k1 p) g k q = nest_ k1 (aboveNest p g (k -# k1) q)
609 -- p can't be Empty, so no need for mkNest
611 aboveNest (NilAbove p) g k q = nilAbove_ (aboveNest p g k q)
612 aboveNest (TextBeside s sl p) g k q = textBeside_ s sl rest
616 Empty -> nilAboveNest g k1 q
617 _ -> aboveNest p g k1 q
618 aboveNest _ _ _ _ = panic "aboveNest: Unhandled case"
622 nilAboveNest :: Bool -> FastInt -> RDoc -> RDoc
623 -- Specification: text s <> nilaboveNest g k q
624 -- = text s <> (text "" $g$ nest k q)
626 nilAboveNest _ _ Empty = Empty -- Here's why the "text s <>" is in the spec!
627 nilAboveNest g k (Nest k1 q) = nilAboveNest g (k +# k1) q
629 nilAboveNest g k q | (not g) && (k ># _ILIT(0)) -- No newline if no overlap
630 = textBeside_ (Str (spaces k)) k q
631 | otherwise -- Put them really above
632 = nilAbove_ (mkNest k q)
636 *********************************************************
638 \subsection{Horizontal composition @<>@}
640 *********************************************************
643 p <> q = Beside p False q
644 p <+> q = Beside p True q
646 beside :: Doc -> Bool -> RDoc -> RDoc
647 -- Specification: beside g p q = p <g> q
649 beside NoDoc _ _ = NoDoc
650 beside (p1 `Union` p2) g q = (beside p1 g q) `union_` (beside p2 g q)
652 beside (Nest k p) g q = nest_ k $! beside p g q -- p non-empty
653 beside p@(Beside p1 g1 q1) g2 q2
654 {- (A `op1` B) `op2` C == A `op1` (B `op2` C) iff op1 == op2
655 [ && (op1 == <> || op1 == <+>) ] -}
656 | g1 == g2 = beside p1 g1 $! beside q1 g2 q2
657 | otherwise = beside (reduceDoc p) g2 q2
658 beside p@(Above _ _ _) g q = let d = reduceDoc p in d `seq` beside d g q
659 beside (NilAbove p) g q = nilAbove_ $! beside p g q
660 beside (TextBeside s sl p) g q = textBeside_ s sl $! rest
663 Empty -> nilBeside g q
668 nilBeside :: Bool -> RDoc -> RDoc
669 -- Specification: text "" <> nilBeside g p
672 nilBeside _ Empty = Empty -- Hence the text "" in the spec
673 nilBeside g (Nest _ p) = nilBeside g p
674 nilBeside g p | g = textBeside_ space_text (_ILIT(1)) p
678 *********************************************************
680 \subsection{Separate, @sep@, Hughes version}
682 *********************************************************
685 -- Specification: sep ps = oneLiner (hsep ps)
689 sep = sepX True -- Separate with spaces
690 cat = sepX False -- Don't
692 sepX :: Bool -> [Doc] -> Doc
694 sepX x (p:ps) = sep1 x (reduceDoc p) (_ILIT(0)) ps
697 -- Specification: sep1 g k ys = sep (x : map (nest k) ys)
698 -- = oneLiner (x <g> nest k (hsep ys))
699 -- `union` x $$ nest k (vcat ys)
701 sep1 :: Bool -> RDoc -> FastInt -> [Doc] -> RDoc
702 sep1 _ NoDoc _ _ = NoDoc
703 sep1 g (p `Union` q) k ys = sep1 g p k ys
705 (aboveNest q False k (reduceDoc (vcat ys)))
707 sep1 g Empty k ys = mkNest k (sepX g ys)
708 sep1 g (Nest n p) k ys = nest_ n (sep1 g p (k -# n) ys)
710 sep1 _ (NilAbove p) k ys = nilAbove_ (aboveNest p False k (reduceDoc (vcat ys)))
711 sep1 g (TextBeside s sl p) k ys = textBeside_ s sl (sepNB g p (k -# sl) ys)
712 sep1 _ _ _ _ = panic "sep1: Unhandled case"
714 -- Specification: sepNB p k ys = sep1 (text "" <> p) k ys
715 -- Called when we have already found some text in the first item
716 -- We have to eat up nests
718 sepNB :: Bool -> Doc -> FastInt -> [Doc] -> Doc
719 sepNB g (Nest _ p) k ys = sepNB g p k ys
721 sepNB g Empty k ys = oneLiner (nilBeside g (reduceDoc rest))
723 nilAboveNest False k (reduceDoc (vcat ys))
726 | otherwise = hcat ys
728 sepNB g p k ys = sep1 g p k ys
731 *********************************************************
735 *********************************************************
744 -- fill (p1:p2:ps) = oneLiner p1 <#> nest (length p1)
745 -- (fill (oneLiner p2 : ps))
749 fill :: Bool -> [Doc] -> Doc
751 fill g (p:ps) = fill1 g (reduceDoc p) (_ILIT(0)) ps
754 fill1 :: Bool -> RDoc -> FastInt -> [Doc] -> Doc
755 fill1 _ NoDoc _ _ = NoDoc
756 fill1 g (p `Union` q) k ys = fill1 g p k ys
758 (aboveNest q False k (fill g ys))
760 fill1 g Empty k ys = mkNest k (fill g ys)
761 fill1 g (Nest n p) k ys = nest_ n (fill1 g p (k -# n) ys)
763 fill1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (fill g ys))
764 fill1 g (TextBeside s sl p) k ys = textBeside_ s sl (fillNB g p (k -# sl) ys)
765 fill1 _ _ _ _ = panic "fill1: Unhandled case"
767 fillNB :: Bool -> Doc -> Int# -> [Doc] -> Doc
768 fillNB g (Nest _ p) k ys = fillNB g p k ys
769 fillNB _ Empty _ [] = Empty
770 fillNB g Empty k (y:ys) = nilBeside g (fill1 g (oneLiner (reduceDoc y)) k1 ys)
772 nilAboveNest False k (fill g (y:ys))
774 k1 | g = k -# _ILIT(1)
777 fillNB g p k ys = fill1 g p k ys
781 *********************************************************
783 \subsection{Selecting the best layout}
785 *********************************************************
788 best :: Int -- Line length
789 -> Int -- Ribbon length
791 -> RDoc -- No unions in here!
797 get :: FastInt -- (Remaining) width of line
801 get w (NilAbove p) = nilAbove_ (get w p)
802 get w (TextBeside s sl p) = textBeside_ s sl (get1 w sl p)
803 get w (Nest k p) = nest_ k (get (w -# k) p)
804 get w (p `Union` q) = nicest w r (get w p) (get w q)
805 get _ _ = panic "best/get: Unhandled case"
807 get1 :: FastInt -- (Remaining) width of line
808 -> FastInt -- Amount of first line already eaten up
809 -> Doc -- This is an argument to TextBeside => eat Nests
810 -> Doc -- No unions in here!
812 get1 _ _ Empty = Empty
813 get1 _ _ NoDoc = NoDoc
814 get1 w sl (NilAbove p) = nilAbove_ (get (w -# sl) p)
815 get1 w sl (TextBeside t tl p) = textBeside_ t tl (get1 w (sl +# tl) p)
816 get1 w sl (Nest _ p) = get1 w sl p
817 get1 w sl (p `Union` q) = nicest1 w r sl (get1 w sl p)
819 get1 _ _ _ = panic "best/get1: Unhandled case"
821 nicest :: FastInt -> FastInt -> Doc -> Doc -> Doc
822 nicest w r p q = nicest1 w r (_ILIT(0)) p q
823 nicest1 :: FastInt -> FastInt -> Int# -> Doc -> Doc -> Doc
824 nicest1 w r sl p q | fits ((w `minFastInt` r) -# sl) p = p
827 fits :: FastInt -- Space available
829 -> Bool -- True if *first line* of Doc fits in space available
831 fits n _ | n <# _ILIT(0) = False
834 fits _ (NilAbove _) = True
835 fits n (TextBeside _ sl p) = fits (n -# sl) p
836 fits _ _ = panic "fits: Unhandled case"
839 @first@ and @nonEmptySet@ are similar to @nicest@ and @fits@, only simpler.
840 @first@ returns its first argument if it is non-empty, otherwise its second.
843 first :: Doc -> Doc -> Doc
844 first p q | nonEmptySet p = p
847 nonEmptySet :: Doc -> Bool
848 nonEmptySet NoDoc = False
849 nonEmptySet (_ `Union` _) = True
850 nonEmptySet Empty = True
851 nonEmptySet (NilAbove _) = True -- NoDoc always in first line
852 nonEmptySet (TextBeside _ _ p) = nonEmptySet p
853 nonEmptySet (Nest _ p) = nonEmptySet p
854 nonEmptySet _ = panic "nonEmptySet: Unhandled case"
857 @oneLiner@ returns the one-line members of the given set of @Doc@s.
860 oneLiner :: Doc -> Doc
861 oneLiner NoDoc = NoDoc
862 oneLiner Empty = Empty
863 oneLiner (NilAbove _) = NoDoc
864 oneLiner (TextBeside s sl p) = textBeside_ s sl (oneLiner p)
865 oneLiner (Nest k p) = nest_ k (oneLiner p)
866 oneLiner (p `Union` _) = oneLiner p
867 oneLiner _ = panic "oneLiner: Unhandled case"
872 *********************************************************
874 \subsection{Displaying the best layout}
876 *********************************************************
881 renderStyle Style{mode, lineLength, ribbonsPerLine} doc
882 = fullRender mode lineLength ribbonsPerLine doc ""
885 render doc = showDocWith PageMode doc
887 showDoc :: Doc -> String -> String
888 showDoc doc rest = showDocWithAppend PageMode doc rest
890 showDocWithAppend :: Mode -> Doc -> String -> String
891 showDocWithAppend mode doc rest = fullRender mode 100 1.5 string_txt rest doc
893 showDocWith :: Mode -> Doc -> String
894 showDocWith mode doc = showDocWithAppend mode doc ""
896 string_txt :: TextDetails -> String -> String
897 string_txt (Chr c) s = c:s
898 string_txt (Str s1) s2 = s1 ++ s2
899 string_txt (PStr s1) s2 = unpackFS s1 ++ s2
900 string_txt (LStr s1 _) s2 = unpackLitString s1 ++ s2
905 fullRender OneLineMode _ _ txt end doc
906 = lay (reduceDoc doc)
908 lay NoDoc = cant_fail
909 lay (Union _ q) = lay q -- Second arg can't be NoDoc
910 lay (Nest _ p) = lay p
912 lay (NilAbove p) = space_text `txt` lay p -- NoDoc always on
914 lay (TextBeside s _ p) = s `txt` lay p
915 lay _ = panic "fullRender/OneLineMode/lay: Unhandled case"
917 fullRender LeftMode _ _ txt end doc
918 = lay (reduceDoc doc)
920 lay NoDoc = cant_fail
921 lay (Union p q) = lay (first p q)
922 lay (Nest _ p) = lay p
924 lay (NilAbove p) = nl_text `txt` lay p -- NoDoc always on first line
925 lay (TextBeside s _ p) = s `txt` lay p
926 lay _ = panic "fullRender/LeftMode/lay: Unhandled case"
928 fullRender mode line_length ribbons_per_line txt end doc
929 = display mode line_length ribbon_length txt end best_doc
931 best_doc = best hacked_line_length ribbon_length (reduceDoc doc)
933 hacked_line_length, ribbon_length :: Int
934 ribbon_length = round (fromIntegral line_length / ribbons_per_line)
935 hacked_line_length = case mode of
936 ZigZagMode -> maxBound
939 display :: Mode -> Int -> Int -> (TextDetails -> t -> t) -> t -> Doc -> t
940 display mode page_width ribbon_width txt end doc
941 = case (iUnbox page_width) -# (iUnbox ribbon_width) of { gap_width ->
942 case gap_width `quotFastInt` _ILIT(2) of { shift ->
944 lay k (Nest k1 p) = lay (k +# k1) p
947 lay k (NilAbove p) = nl_text `txt` lay k p
949 lay k (TextBeside s sl p)
951 ZigZagMode | k >=# gap_width
953 Str (multi_ch shift '/') `txt` (
955 lay1 (k -# shift) s sl p)))
959 Str (multi_ch shift '\\') `txt` (
961 lay1 (k +# shift) s sl p )))
964 lay _ _ = panic "display/lay: Unhandled case"
966 lay1 k s sl p = indent k (s `txt` lay2 (k +# sl) p)
968 lay2 k (NilAbove p) = nl_text `txt` lay k p
969 lay2 k (TextBeside s sl p) = s `txt` (lay2 (k +# sl) p)
970 lay2 k (Nest _ p) = lay2 k p
972 lay2 _ _ = panic "display/lay2: Unhandled case"
974 -- optimise long indentations using LitString chunks of 8 spaces
975 indent n r | n >=# _ILIT(8) = LStr (sLit " ") (_ILIT(8)) `txt`
976 indent (n -# _ILIT(8)) r
977 | otherwise = Str (spaces n) `txt` r
983 cant_fail = error "easy_display: NoDoc"
985 multi_ch :: Int# -> Char -> String
986 multi_ch n ch | n <=# _ILIT(0) = ""
987 | otherwise = ch : multi_ch (n -# _ILIT(1)) ch
989 spaces :: Int# -> String
990 spaces n | n <=# _ILIT(0) = ""
991 | otherwise = ' ' : spaces (n -# _ILIT(1))
997 pprCols = 120 -- could make configurable
999 printDoc :: Mode -> Handle -> Doc -> IO ()
1000 printDoc LeftMode hdl doc
1001 = do { printLeftRender hdl doc; hFlush hdl }
1002 printDoc mode hdl doc
1003 = do { fullRender mode pprCols 1.5 put done doc ;
1006 put (Chr c) next = hPutChar hdl c >> next
1007 put (Str s) next = hPutStr hdl s >> next
1008 put (PStr s) next = hPutFS hdl s >> next
1009 put (LStr s l) next = hPutLitString hdl s l >> next
1011 done = hPutChar hdl '\n'
1013 -- some versions of hPutBuf will barf if the length is zero
1014 hPutLitString :: Handle -> Ptr a -> Int# -> IO ()
1015 hPutLitString handle a l = if l ==# _ILIT(0)
1017 else hPutBuf handle a (iBox l)
1019 -- Printing output in LeftMode is performance critical: it's used when
1020 -- dumping C and assembly output, so we allow ourselves a few dirty
1023 -- (1) we specialise fullRender for LeftMode with IO output.
1025 -- (2) we add a layer of buffering on top of Handles. Handles
1026 -- don't perform well with lots of hPutChars, which is mostly
1027 -- what we're doing here, because Handles have to be thread-safe
1028 -- and async exception-safe. We only have a single thread and don't
1029 -- care about exceptions, so we add a layer of fast buffering
1030 -- over the Handle interface.
1032 -- (3) a few hacks in layLeft below to convince GHC to generate the right
1035 printLeftRender :: Handle -> Doc -> IO ()
1036 printLeftRender hdl doc = do
1037 b <- newBufHandle hdl
1038 layLeft b (reduceDoc doc)
1041 -- HACK ALERT! the "return () >>" below convinces GHC to eta-expand
1042 -- this function with the IO state lambda. Otherwise we end up with
1043 -- closures in all the case branches.
1044 layLeft :: BufHandle -> Doc -> IO ()
1045 layLeft b _ | b `seq` False = undefined -- make it strict in b
1046 layLeft _ NoDoc = cant_fail
1047 layLeft b (Union p q) = return () >> layLeft b (first p q)
1048 layLeft b (Nest _ p) = return () >> layLeft b p
1049 layLeft b Empty = bPutChar b '\n'
1050 layLeft b (NilAbove p) = bPutChar b '\n' >> layLeft b p
1051 layLeft b (TextBeside s _ p) = put b s >> layLeft b p
1053 put b _ | b `seq` False = undefined
1054 put b (Chr c) = bPutChar b c
1055 put b (Str s) = bPutStr b s
1056 put b (PStr s) = bPutFS b s
1057 put b (LStr s l) = bPutLitString b s l
1058 layLeft _ _ = panic "layLeft: Unhandled case"