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
155 {-# OPTIONS -fno-warn-unused-imports #-}
156 -- XXX GHC 6.9 seems to be confused by unpackCString# being used only in
161 Mode(..), TextDetails(..),
163 empty, isEmpty, nest,
165 char, text, ftext, ptext,
166 int, integer, float, double, rational,
167 parens, brackets, braces, quotes, doubleQuotes,
168 semi, comma, colon, space, equals,
169 lparen, rparen, lbrack, rbrack, lbrace, rbrace, cparen,
171 (<>), (<+>), hcat, hsep,
178 -- renderStyle, -- Haskell 1.3 only
179 render, fullRender, printDoc, showDocWith
187 import Numeric (fromRat)
189 --import Foreign.Ptr (castPtr)
191 #if defined(__GLASGOW_HASKELL__)
193 import GHC.Base ( unpackCString# )
194 import GHC.Exts ( Int# )
195 import GHC.Ptr ( Ptr(..) )
198 -- Don't import Util( assertPanic ) because it makes a loop in the module structure
208 -- Disable ASSERT checks; they are expensive!
209 #define LOCAL_ASSERT(x)
214 %*********************************************************
216 \subsection{The interface}
218 %*********************************************************
220 The primitive @Doc@ values
224 isEmpty :: Doc -> Bool
225 text :: String -> Doc
228 semi, comma, colon, space, equals :: Doc
229 lparen, rparen, lbrack, rbrack, lbrace, rbrace :: Doc
231 parens, brackets, braces :: Doc -> Doc
232 quotes, doubleQuotes :: Doc -> Doc
235 integer :: Integer -> Doc
236 float :: Float -> Doc
237 double :: Double -> Doc
238 rational :: Rational -> Doc
241 Combining @Doc@ values
244 (<>) :: Doc -> Doc -> Doc -- Beside
245 hcat :: [Doc] -> Doc -- List version of <>
246 (<+>) :: Doc -> Doc -> Doc -- Beside, separated by space
247 hsep :: [Doc] -> Doc -- List version of <+>
249 ($$) :: Doc -> Doc -> Doc -- Above; if there is no
250 -- overlap it "dovetails" the two
251 vcat :: [Doc] -> Doc -- List version of $$
253 cat :: [Doc] -> Doc -- Either hcat or vcat
254 sep :: [Doc] -> Doc -- Either hsep or vcat
255 fcat :: [Doc] -> Doc -- ``Paragraph fill'' version of cat
256 fsep :: [Doc] -> Doc -- ``Paragraph fill'' version of sep
258 nest :: Int -> Doc -> Doc -- Nested
264 hang :: Doc -> Int -> Doc -> Doc
265 punctuate :: Doc -> [Doc] -> [Doc] -- punctuate p [d1, ... dn] = [d1 <> p, d2 <> p, ... dn-1 <> p, dn]
268 Displaying @Doc@ values.
271 instance Show Doc where
272 showsPrec _ doc cont = showDoc doc cont
274 render :: Doc -> String -- Uses default style
276 -> Int -- Line length
277 -> Float -- Ribbons per line
278 -> (TextDetails -> a -> a) -- What to do with text
279 -> a -- What to do at the end
283 {- When we start using 1.3
284 renderStyle :: Style -> Doc -> String
285 data Style = Style { lineLength :: Int, -- In chars
286 ribbonsPerLine :: Float, -- Ratio of ribbon length to line length
289 style :: Style -- The default style
290 style = Style { lineLength = 100, ribbonsPerLine = 2.5, mode = PageMode }
293 data Mode = PageMode -- Normal
294 | ZigZagMode -- With zig-zag cuts
295 | LeftMode -- No indentation, infinitely long lines
296 | OneLineMode -- All on one line
301 %*********************************************************
303 \subsection{The @Doc@ calculus}
305 %*********************************************************
307 The @Doc@ combinators satisfy the following laws:
311 <a1> (x $$ y) $$ z = x $$ (y $$ z)
319 <b1> (x <> y) <> z = x <> (y <> z)
320 <b2> empty <> x = empty
327 <t1> text s <> text t = text (s++t)
328 <t2> text "" <> x = x, if x non-empty
333 <n2> nest k (nest k' x) = nest (k+k') x
334 <n3> nest k (x <> y) = nest k z <> nest k y
335 <n4> nest k (x $$ y) = nest k x $$ nest k y
336 <n5> nest k empty = empty
337 <n6> x <> nest k y = x <> y, if x non-empty
339 - Note the side condition on <n6>! It is this that
340 makes it OK for empty to be a left unit for <>.
344 <m1> (text s <> x) $$ y = text s <> ((text "" <> x)) $$
347 <m2> (x $$ y) <> z = x $$ (y <> z)
351 Laws for list versions
352 ~~~~~~~~~~~~~~~~~~~~~~
353 <l1> sep (ps++[empty]++qs) = sep (ps ++ qs)
354 ...ditto hsep, hcat, vcat, fill...
356 <l2> nest k (sep ps) = sep (map (nest k) ps)
357 ...ditto hsep, hcat, vcat, fill...
361 <o1> oneLiner (nest k p) = nest k (oneLiner p)
362 <o2> oneLiner (x <> y) = oneLiner x <> oneLiner y
366 You might think that the following verion of <m1> would
369 <3 NO> (text s <> x) $$ y = text s <> ((empty <> x)) $$
372 But it doesn't work, for if x=empty, we would have
374 text s $$ y = text s <> (empty $$ nest (-length s) y)
375 = text s <> nest (-length s) y
380 %*********************************************************
382 \subsection{Simple derived definitions}
384 %*********************************************************
399 int n = text (show n)
400 integer n = text (show n)
401 float n = text (show n)
402 double n = text (show n)
403 rational n = text (show (fromRat n :: Double))
404 --rational n = text (show (fromRationalX n)) -- _showRational 30 n)
406 quotes p = char '`' <> p <> char '\''
407 doubleQuotes p = char '"' <> p <> char '"'
408 parens p = char '(' <> p <> char ')'
409 brackets p = char '[' <> p <> char ']'
410 braces p = char '{' <> p <> char '}'
412 cparen :: Bool -> Doc -> Doc
416 hcat = foldr (<>) empty
417 hsep = foldr (<+>) empty
418 vcat = foldr ($$) empty
420 hang d1 n d2 = sep [d1, nest n d2]
423 punctuate p (d:ds) = go d ds
426 go d (e:es) = (d <> p) : go e es
430 %*********************************************************
432 \subsection{The @Doc@ data type}
434 %*********************************************************
436 A @Doc@ represents a {\em set} of layouts. A @Doc@ with
437 no occurrences of @Union@ or @NoDoc@ represents just one layout.
441 | NilAbove Doc -- text "" $$ x
442 | TextBeside !TextDetails FastInt Doc -- text s <> x
443 | Nest FastInt Doc -- nest k x
444 | Union Doc Doc -- ul `union` ur
445 | NoDoc -- The empty set of documents
446 | Beside Doc Bool Doc -- True <=> space between
447 | Above Doc Bool Doc -- True <=> never overlap
449 type RDoc = Doc -- RDoc is a "reduced Doc", guaranteed not to have a top-level Above or Beside
452 reduceDoc :: Doc -> RDoc
453 reduceDoc (Beside p g q) = beside p g (reduceDoc q)
454 reduceDoc (Above p g q) = above p g (reduceDoc q)
458 data TextDetails = Chr {-#UNPACK#-}!Char
460 | PStr FastString -- a hashed string
461 | LStr {-#UNPACK#-}!LitString FastInt -- a '\0'-terminated
464 space_text :: TextDetails
466 nl_text :: TextDetails
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_ :: Doc -> Doc
505 nilAbove_ p = LOCAL_ASSERT( _ok p ) NilAbove p
510 -- Arg of a TextBeside is always an RDoc
511 textBeside_ :: TextDetails -> FastInt -> Doc -> Doc
512 textBeside_ s sl p = TextBeside s sl (LOCAL_ASSERT( _ok p ) p)
514 _ok (Nest _ _) = False
517 -- Arg of Nest is always an RDoc
518 nest_ :: FastInt -> Doc -> Doc
519 nest_ k p = Nest k (LOCAL_ASSERT( _ok p ) p)
524 -- Args of union are always RDocs
525 union_ :: Doc -> Doc -> Doc
526 union_ p q = Union (LOCAL_ASSERT( _ok p ) p) (LOCAL_ASSERT( _ok q ) q)
528 _ok (TextBeside _ _ _) = True
529 _ok (NilAbove _) = True
530 _ok (Union _ _) = True
534 Notice the difference between
535 * NoDoc (no documents)
536 * Empty (one empty document; no height and no width)
537 * text "" (a document containing the empty string;
538 one line high, but has no width)
542 %*********************************************************
544 \subsection{@empty@, @text@, @nest@, @union@}
546 %*********************************************************
554 char c = textBeside_ (Chr c) (_ILIT(1)) Empty
555 text s = case iUnbox (length s) of {sl -> textBeside_ (Str s) sl Empty}
556 ftext :: FastString -> Doc
557 ftext s = case iUnbox (lengthFS s) of {sl -> textBeside_ (PStr s) sl Empty}
558 ptext :: LitString -> Doc
559 ptext s_= case iUnbox (lengthLS s) of {sl -> textBeside_ (LStr s sl) sl Empty}
560 where s = {-castPtr-} s_
562 #if defined(__GLASGOW_HASKELL__)
563 -- RULE that turns (text "abc") into (ptext (A# "abc"#)) to avoid the
564 -- intermediate packing/unpacking of the string.
566 "text/str" forall a. text (unpackCString# a) = ptext (Ptr a)
570 nest k p = mkNest (iUnbox k) (reduceDoc p) -- Externally callable version
572 -- mkNest checks for Nest's invariant that it doesn't have an Empty inside it
573 mkNest :: Int# -> Doc -> Doc
574 mkNest k (Nest k1 p) = mkNest (k +# k1) p
575 mkNest _ NoDoc = NoDoc
576 mkNest _ Empty = Empty
577 mkNest k p | k ==# _ILIT(0) = p -- Worth a try!
578 mkNest k p = nest_ k p
580 -- mkUnion checks for an empty document
581 mkUnion :: Doc -> Doc -> Doc
582 mkUnion Empty _ = Empty
583 mkUnion p q = p `union_` q
586 %*********************************************************
588 \subsection{Vertical composition @$$@}
590 %*********************************************************
594 p $$ q = Above p False q
595 ($+$) :: Doc -> Doc -> Doc
596 p $+$ q = Above p True q
598 above :: Doc -> Bool -> RDoc -> RDoc
599 above (Above p g1 q1) g2 q2 = above p g1 (above q1 g2 q2)
600 above p@(Beside _ _ _) g q = aboveNest (reduceDoc p) g (_ILIT(0)) (reduceDoc q)
601 above p g q = aboveNest p g (_ILIT(0)) (reduceDoc q)
603 aboveNest :: RDoc -> Bool -> FastInt -> RDoc -> RDoc
604 -- Specfication: aboveNest p g k q = p $g$ (nest k q)
606 aboveNest NoDoc _ _ _ = NoDoc
607 aboveNest (p1 `Union` p2) g k q = aboveNest p1 g k q `union_`
610 aboveNest Empty _ k q = mkNest k q
611 aboveNest (Nest k1 p) g k q = nest_ k1 (aboveNest p g (k -# k1) q)
612 -- p can't be Empty, so no need for mkNest
614 aboveNest (NilAbove p) g k q = nilAbove_ (aboveNest p g k q)
615 aboveNest (TextBeside s sl p) g k q = textBeside_ s sl rest
619 Empty -> nilAboveNest g k1 q
620 _ -> aboveNest p g k1 q
621 aboveNest _ _ _ _ = panic "aboveNest: Unhandled case"
625 nilAboveNest :: Bool -> FastInt -> RDoc -> RDoc
626 -- Specification: text s <> nilaboveNest g k q
627 -- = text s <> (text "" $g$ nest k q)
629 nilAboveNest _ _ Empty = Empty -- Here's why the "text s <>" is in the spec!
630 nilAboveNest g k (Nest k1 q) = nilAboveNest g (k +# k1) q
632 nilAboveNest g k q | (not g) && (k ># _ILIT(0)) -- No newline if no overlap
633 = textBeside_ (Str (spaces k)) k q
634 | otherwise -- Put them really above
635 = nilAbove_ (mkNest k q)
639 %*********************************************************
641 \subsection{Horizontal composition @<>@}
643 %*********************************************************
646 p <> q = Beside p False q
647 p <+> q = Beside p True q
649 beside :: Doc -> Bool -> RDoc -> RDoc
650 -- Specification: beside g p q = p <g> q
652 beside NoDoc _ _ = NoDoc
653 beside (p1 `Union` p2) g q = (beside p1 g q) `union_` (beside p2 g q)
655 beside (Nest k p) g q = nest_ k $! beside p g q -- p non-empty
656 beside p@(Beside p1 g1 q1) g2 q2
657 {- (A `op1` B) `op2` C == A `op1` (B `op2` C) iff op1 == op2
658 [ && (op1 == <> || op1 == <+>) ] -}
659 | g1 == g2 = beside p1 g1 $! beside q1 g2 q2
660 | otherwise = beside (reduceDoc p) g2 q2
661 beside p@(Above _ _ _) g q = let d = reduceDoc p in d `seq` beside d g q
662 beside (NilAbove p) g q = nilAbove_ $! beside p g q
663 beside (TextBeside s sl p) g q = textBeside_ s sl $! rest
666 Empty -> nilBeside g q
671 nilBeside :: Bool -> RDoc -> RDoc
672 -- Specification: text "" <> nilBeside g p
675 nilBeside _ Empty = Empty -- Hence the text "" in the spec
676 nilBeside g (Nest _ p) = nilBeside g p
677 nilBeside g p | g = textBeside_ space_text (_ILIT(1)) p
681 %*********************************************************
683 \subsection{Separate, @sep@, Hughes version}
685 %*********************************************************
688 -- Specification: sep ps = oneLiner (hsep ps)
692 sep = sepX True -- Separate with spaces
693 cat = sepX False -- Don't
695 sepX :: Bool -> [Doc] -> Doc
697 sepX x (p:ps) = sep1 x (reduceDoc p) (_ILIT(0)) ps
700 -- Specification: sep1 g k ys = sep (x : map (nest k) ys)
701 -- = oneLiner (x <g> nest k (hsep ys))
702 -- `union` x $$ nest k (vcat ys)
704 sep1 :: Bool -> RDoc -> FastInt -> [Doc] -> RDoc
705 sep1 _ NoDoc _ _ = NoDoc
706 sep1 g (p `Union` q) k ys = sep1 g p k ys
708 (aboveNest q False k (reduceDoc (vcat ys)))
710 sep1 g Empty k ys = mkNest k (sepX g ys)
711 sep1 g (Nest n p) k ys = nest_ n (sep1 g p (k -# n) ys)
713 sep1 _ (NilAbove p) k ys = nilAbove_ (aboveNest p False k (reduceDoc (vcat ys)))
714 sep1 g (TextBeside s sl p) k ys = textBeside_ s sl (sepNB g p (k -# sl) ys)
715 sep1 _ _ _ _ = panic "sep1: Unhandled case"
717 -- Specification: sepNB p k ys = sep1 (text "" <> p) k ys
718 -- Called when we have already found some text in the first item
719 -- We have to eat up nests
721 sepNB :: Bool -> Doc -> FastInt -> [Doc] -> Doc
722 sepNB g (Nest _ p) k ys = sepNB g p k ys
724 sepNB g Empty k ys = oneLiner (nilBeside g (reduceDoc rest))
726 nilAboveNest False k (reduceDoc (vcat ys))
729 | otherwise = hcat ys
731 sepNB g p k ys = sep1 g p k ys
734 %*********************************************************
738 %*********************************************************
747 -- fill (p1:p2:ps) = oneLiner p1 <#> nest (length p1)
748 -- (fill (oneLiner p2 : ps))
752 fill :: Bool -> [Doc] -> Doc
754 fill g (p:ps) = fill1 g (reduceDoc p) (_ILIT(0)) ps
757 fill1 :: Bool -> RDoc -> FastInt -> [Doc] -> Doc
758 fill1 _ NoDoc _ _ = NoDoc
759 fill1 g (p `Union` q) k ys = fill1 g p k ys
761 (aboveNest q False k (fill g ys))
763 fill1 g Empty k ys = mkNest k (fill g ys)
764 fill1 g (Nest n p) k ys = nest_ n (fill1 g p (k -# n) ys)
766 fill1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (fill g ys))
767 fill1 g (TextBeside s sl p) k ys = textBeside_ s sl (fillNB g p (k -# sl) ys)
768 fill1 _ _ _ _ = panic "fill1: Unhandled case"
770 fillNB :: Bool -> Doc -> Int# -> [Doc] -> Doc
771 fillNB g (Nest _ p) k ys = fillNB g p k ys
772 fillNB _ Empty _ [] = Empty
773 fillNB g Empty k (y:ys) = nilBeside g (fill1 g (oneLiner (reduceDoc y)) k1 ys)
775 nilAboveNest False k (fill g (y:ys))
777 k1 | g = k -# _ILIT(1)
780 fillNB g p k ys = fill1 g p k ys
784 %*********************************************************
786 \subsection{Selecting the best layout}
788 %*********************************************************
791 best :: Int -- Line length
792 -> Int -- Ribbon length
794 -> RDoc -- No unions in here!
800 get :: FastInt -- (Remaining) width of line
804 get w (NilAbove p) = nilAbove_ (get w p)
805 get w (TextBeside s sl p) = textBeside_ s sl (get1 w sl p)
806 get w (Nest k p) = nest_ k (get (w -# k) p)
807 get w (p `Union` q) = nicest w r (get w p) (get w q)
808 get _ _ = panic "best/get: Unhandled case"
810 get1 :: FastInt -- (Remaining) width of line
811 -> FastInt -- Amount of first line already eaten up
812 -> Doc -- This is an argument to TextBeside => eat Nests
813 -> Doc -- No unions in here!
815 get1 _ _ Empty = Empty
816 get1 _ _ NoDoc = NoDoc
817 get1 w sl (NilAbove p) = nilAbove_ (get (w -# sl) p)
818 get1 w sl (TextBeside t tl p) = textBeside_ t tl (get1 w (sl +# tl) p)
819 get1 w sl (Nest _ p) = get1 w sl p
820 get1 w sl (p `Union` q) = nicest1 w r sl (get1 w sl p)
822 get1 _ _ _ = panic "best/get1: Unhandled case"
824 nicest :: FastInt -> FastInt -> Doc -> Doc -> Doc
825 nicest w r p q = nicest1 w r (_ILIT(0)) p q
826 nicest1 :: FastInt -> FastInt -> Int# -> Doc -> Doc -> Doc
827 nicest1 w r sl p q | fits ((w `minFastInt` r) -# sl) p = p
830 fits :: FastInt -- Space available
832 -> Bool -- True if *first line* of Doc fits in space available
834 fits n _ | n <# _ILIT(0) = False
837 fits _ (NilAbove _) = True
838 fits n (TextBeside _ sl p) = fits (n -# sl) p
839 fits _ _ = panic "fits: Unhandled case"
842 @first@ and @nonEmptySet@ are similar to @nicest@ and @fits@, only simpler.
843 @first@ returns its first argument if it is non-empty, otherwise its second.
846 first :: Doc -> Doc -> Doc
847 first p q | nonEmptySet p = p
850 nonEmptySet :: Doc -> Bool
851 nonEmptySet NoDoc = False
852 nonEmptySet (_ `Union` _) = True
853 nonEmptySet Empty = True
854 nonEmptySet (NilAbove _) = True -- NoDoc always in first line
855 nonEmptySet (TextBeside _ _ p) = nonEmptySet p
856 nonEmptySet (Nest _ p) = nonEmptySet p
857 nonEmptySet _ = panic "nonEmptySet: Unhandled case"
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 _) = 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` _) = oneLiner p
870 oneLiner _ = panic "oneLiner: Unhandled case"
875 %*********************************************************
877 \subsection{Displaying the best layout}
879 %*********************************************************
884 renderStyle Style{mode, lineLength, ribbonsPerLine} doc
885 = fullRender mode lineLength ribbonsPerLine doc ""
888 render doc = showDocWith PageMode doc
890 showDoc :: Doc -> String -> String
891 showDoc doc rest = showDocWithAppend PageMode doc rest
893 showDocWithAppend :: Mode -> Doc -> String -> String
894 showDocWithAppend mode doc rest = fullRender mode 100 1.5 string_txt rest doc
896 showDocWith :: Mode -> Doc -> String
897 showDocWith mode doc = showDocWithAppend mode doc ""
899 string_txt :: TextDetails -> String -> String
900 string_txt (Chr c) s = c:s
901 string_txt (Str s1) s2 = s1 ++ s2
902 string_txt (PStr s1) s2 = unpackFS s1 ++ s2
903 string_txt (LStr s1 _) s2 = unpackLitString s1 ++ s2
908 fullRender OneLineMode _ _ txt end doc
909 = lay (reduceDoc doc)
911 lay NoDoc = cant_fail
912 lay (Union _ q) = lay q -- Second arg can't be NoDoc
913 lay (Nest _ p) = lay p
915 lay (NilAbove p) = space_text `txt` lay p -- NoDoc always on
917 lay (TextBeside s _ p) = s `txt` lay p
918 lay _ = panic "fullRender/OneLineMode/lay: Unhandled case"
920 fullRender LeftMode _ _ txt end doc
921 = lay (reduceDoc doc)
923 lay NoDoc = cant_fail
924 lay (Union p q) = lay (first p q)
925 lay (Nest _ p) = lay p
927 lay (NilAbove p) = nl_text `txt` lay p -- NoDoc always on first line
928 lay (TextBeside s _ p) = s `txt` lay p
929 lay _ = panic "fullRender/LeftMode/lay: Unhandled case"
931 fullRender mode line_length ribbons_per_line txt end doc
932 = display mode line_length ribbon_length txt end best_doc
934 best_doc = best hacked_line_length ribbon_length (reduceDoc doc)
936 hacked_line_length, ribbon_length :: Int
937 ribbon_length = round (fromIntegral line_length / ribbons_per_line)
938 hacked_line_length = case mode of
939 ZigZagMode -> maxBound
942 display :: Mode -> Int -> Int -> (TextDetails -> t -> t) -> t -> Doc -> t
943 display mode page_width ribbon_width txt end doc
944 = case (iUnbox page_width) -# (iUnbox ribbon_width) of { gap_width ->
945 case gap_width `quotFastInt` _ILIT(2) of { shift ->
947 lay k (Nest k1 p) = lay (k +# k1) p
950 lay k (NilAbove p) = nl_text `txt` lay k p
952 lay k (TextBeside s sl p)
954 ZigZagMode | k >=# gap_width
956 Str (multi_ch shift '/') `txt` (
958 lay1 (k -# shift) s sl p)))
962 Str (multi_ch shift '\\') `txt` (
964 lay1 (k +# shift) s sl p )))
967 lay _ _ = panic "display/lay: Unhandled case"
969 lay1 k s sl p = indent k (s `txt` lay2 (k +# sl) p)
971 lay2 k (NilAbove p) = nl_text `txt` lay k p
972 lay2 k (TextBeside s sl p) = s `txt` (lay2 (k +# sl) p)
973 lay2 k (Nest _ p) = lay2 k p
975 lay2 _ _ = panic "display/lay2: Unhandled case"
977 -- optimise long indentations using LitString chunks of 8 spaces
978 indent n r | n >=# _ILIT(8) = LStr (sLit " ") (_ILIT(8)) `txt`
979 indent (n -# _ILIT(8)) r
980 | otherwise = Str (spaces n) `txt` r
986 cant_fail = error "easy_display: NoDoc"
988 multi_ch :: Int# -> Char -> String
989 multi_ch n ch | n <=# _ILIT(0) = ""
990 | otherwise = ch : multi_ch (n -# _ILIT(1)) ch
992 spaces :: Int# -> String
993 spaces n | n <=# _ILIT(0) = ""
994 | otherwise = ' ' : spaces (n -# _ILIT(1))
1000 pprCols = 100 -- could make configurable
1002 -- NB. printDoc prints FastStrings in UTF-8: hPutFS below does no decoding.
1003 -- This is what we usually want, because the IO library has no encoding
1004 -- functionality, and we're assuming UTF-8 source code so we might as well
1005 -- assume UTF-8 output too.
1006 printDoc :: Mode -> Handle -> Doc -> IO ()
1007 printDoc LeftMode hdl doc
1008 = do { printLeftRender hdl doc; hFlush hdl }
1009 printDoc mode hdl doc
1010 = do { fullRender mode pprCols 1.5 put done doc ;
1013 put (Chr c) next = hPutChar hdl c >> next
1014 put (Str s) next = hPutStr hdl s >> next
1015 put (PStr s) next = hPutFS hdl s >> next
1016 put (LStr s l) next = hPutLitString hdl s l >> next
1018 done = hPutChar hdl '\n'
1020 -- some versions of hPutBuf will barf if the length is zero
1021 hPutLitString :: Handle -> Ptr a -> Int# -> IO ()
1022 hPutLitString handle a l = if l ==# _ILIT(0)
1024 else hPutBuf handle a (iBox l)
1026 -- Printing output in LeftMode is performance critical: it's used when
1027 -- dumping C and assembly output, so we allow ourselves a few dirty
1030 -- (1) we specialise fullRender for LeftMode with IO output.
1032 -- (2) we add a layer of buffering on top of Handles. Handles
1033 -- don't perform well with lots of hPutChars, which is mostly
1034 -- what we're doing here, because Handles have to be thread-safe
1035 -- and async exception-safe. We only have a single thread and don't
1036 -- care about exceptions, so we add a layer of fast buffering
1037 -- over the Handle interface.
1039 -- (3) a few hacks in layLeft below to convince GHC to generate the right
1042 printLeftRender :: Handle -> Doc -> IO ()
1043 printLeftRender hdl doc = do
1044 b <- newBufHandle hdl
1045 layLeft b (reduceDoc doc)
1048 -- HACK ALERT! the "return () >>" below convinces GHC to eta-expand
1049 -- this function with the IO state lambda. Otherwise we end up with
1050 -- closures in all the case branches.
1051 layLeft :: BufHandle -> Doc -> IO ()
1052 layLeft b _ | b `seq` False = undefined -- make it strict in b
1053 layLeft _ NoDoc = cant_fail
1054 layLeft b (Union p q) = return () >> layLeft b (first p q)
1055 layLeft b (Nest _ p) = return () >> layLeft b p
1056 layLeft b Empty = bPutChar b '\n'
1057 layLeft b (NilAbove p) = bPutChar b '\n' >> layLeft b p
1058 layLeft b (TextBeside s _ p) = put b s >> layLeft b p
1060 put b _ | b `seq` False = undefined
1061 put b (Chr c) = bPutChar b c
1062 put b (Str s) = bPutStr b s
1063 put b (PStr s) = bPutFS b s
1064 put b (LStr s l) = bPutLitString b s l
1065 layLeft _ _ = panic "layLeft: Unhandled case"