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 $$, and anywhere in the argument list for
85 sep, hcat, hsep, vcat, fcat etc.
87 It is Really Useful in practice.
89 2. There is a paragraph-fill combinator, fsep, that's much like sep,
90 only it keeps fitting things on one line until itc can't fit any more.
92 3. Some random useful extra combinators are provided.
93 <+> puts its arguments beside each other with a space between them,
94 unless either argument is empty in which case it returns the other
97 hcat is a list version of <>
98 hsep is a list version of <+>
99 vcat is a list version of $$
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,
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
178 #include "HsVersions.h"
185 import Numeric (fromRat)
188 import GHC.Base ( unpackCString# )
189 import GHC.Ptr ( Ptr(..) )
191 -- Don't import Util( assertPanic ) because it makes a loop in the module structure
200 *********************************************************
202 \subsection{CPP magic so that we can compile with both GHC and Hugs}
204 *********************************************************
206 The library uses unboxed types to get a bit more speed, but these CPP macros
207 allow you to use either GHC or Hugs. To get GHC, just set the CPP variable
212 #if defined(__GLASGOW_HASKELL__)
216 -- Disable ASSERT checks; they are expensive!
217 #define LOCAL_ASSERT(x)
220 #define IBOX(x) (I# (x))
223 #define NEGATE negateInt#
229 #define DIV `quotInt#`
233 #define MAXINT maxBound
239 #define LOCAL_ASSERT(x)
244 #define NEGATE negate
253 #define MAXINT maxBound
260 *********************************************************
262 \subsection{The interface}
264 *********************************************************
266 The primitive @Doc@ values
270 isEmpty :: Doc -> Bool
271 text :: String -> Doc
274 semi, comma, colon, space, equals :: Doc
275 lparen, rparen, lbrack, rbrack, lbrace, rbrace :: Doc
277 parens, brackets, braces :: Doc -> Doc
278 quotes, doubleQuotes :: Doc -> Doc
281 integer :: Integer -> Doc
282 float :: Float -> Doc
283 double :: Double -> Doc
284 rational :: Rational -> Doc
287 Combining @Doc@ values
290 (<>) :: Doc -> Doc -> Doc -- Beside
291 hcat :: [Doc] -> Doc -- List version of <>
292 (<+>) :: Doc -> Doc -> Doc -- Beside, separated by space
293 hsep :: [Doc] -> Doc -- List version of <+>
295 ($$) :: Doc -> Doc -> Doc -- Above; if there is no
296 -- overlap it "dovetails" the two
297 vcat :: [Doc] -> Doc -- List version of $$
299 cat :: [Doc] -> Doc -- Either hcat or vcat
300 sep :: [Doc] -> Doc -- Either hsep or vcat
301 fcat :: [Doc] -> Doc -- ``Paragraph fill'' version of cat
302 fsep :: [Doc] -> Doc -- ``Paragraph fill'' version of sep
304 nest :: Int -> Doc -> Doc -- Nested
310 hang :: Doc -> Int -> Doc -> Doc
311 punctuate :: Doc -> [Doc] -> [Doc] -- punctuate p [d1, ... dn] = [d1 <> p, d2 <> p, ... dn-1 <> p, dn]
314 Displaying @Doc@ values.
317 instance SHOW Doc where
318 showsPrec prec doc cont = showDoc doc cont
320 render :: Doc -> String -- Uses default style
322 -> Int -- Line length
323 -> Float -- Ribbons per line
324 -> (TextDetails -> a -> a) -- What to do with text
325 -> a -- What to do at the end
329 {- When we start using 1.3
330 renderStyle :: Style -> Doc -> String
331 data Style = Style { lineLength :: Int, -- In chars
332 ribbonsPerLine :: Float, -- Ratio of ribbon length to line length
335 style :: Style -- The default style
336 style = Style { lineLength = 100, ribbonsPerLine = 2.5, mode = PageMode }
339 data Mode = PageMode -- Normal
340 | ZigZagMode -- With zig-zag cuts
341 | LeftMode -- No indentation, infinitely long lines
342 | OneLineMode -- All on one line
347 *********************************************************
349 \subsection{The @Doc@ calculus}
351 *********************************************************
353 The @Doc@ combinators satisfy the following laws:
357 <a1> (x $$ y) $$ z = x $$ (y $$ z)
365 <b1> (x <> y) <> z = x <> (y <> z)
366 <b2> empty <> x = empty
373 <t1> text s <> text t = text (s++t)
374 <t2> text "" <> x = x, if x non-empty
379 <n2> nest k (nest k' x) = nest (k+k') x
380 <n3> nest k (x <> y) = nest k z <> nest k y
381 <n4> nest k (x $$ y) = nest k x $$ nest k y
382 <n5> nest k empty = empty
383 <n6> x <> nest k y = x <> y, if x non-empty
385 ** Note the side condition on <n6>! It is this that
386 ** makes it OK for empty to be a left unit for <>.
390 <m1> (text s <> x) $$ y = text s <> ((text "" <> x)) $$
393 <m2> (x $$ y) <> z = x $$ (y <> z)
397 Laws for list versions
398 ~~~~~~~~~~~~~~~~~~~~~~
399 <l1> sep (ps++[empty]++qs) = sep (ps ++ qs)
400 ...ditto hsep, hcat, vcat, fill...
402 <l2> nest k (sep ps) = sep (map (nest k) ps)
403 ...ditto hsep, hcat, vcat, fill...
407 <o1> oneLiner (nest k p) = nest k (oneLiner p)
408 <o2> oneLiner (x <> y) = oneLiner x <> oneLiner y
412 You might think that the following verion of <m1> would
415 <3 NO> (text s <> x) $$ y = text s <> ((empty <> x)) $$
418 But it doesn't work, for if x=empty, we would have
420 text s $$ y = text s <> (empty $$ nest (-length s) y)
421 = text s <> nest (-length s) y
426 *********************************************************
428 \subsection{Simple derived definitions}
430 *********************************************************
445 int n = text (show n)
446 integer n = text (show n)
447 float n = text (show n)
448 double n = text (show n)
449 rational n = text (show (fromRat n))
450 --rational n = text (show (fromRationalX n)) -- _showRational 30 n)
452 quotes p = char '`' <> p <> char '\''
453 doubleQuotes p = char '"' <> p <> char '"'
454 parens p = char '(' <> p <> char ')'
455 brackets p = char '[' <> p <> char ']'
456 braces p = char '{' <> p <> char '}'
461 hcat = foldr (<>) empty
462 hsep = foldr (<+>) empty
463 vcat = foldr ($$) empty
465 hang d1 n d2 = sep [d1, nest n d2]
468 punctuate p (d:ds) = go d ds
471 go d (e:es) = (d <> p) : go e es
475 *********************************************************
477 \subsection{The @Doc@ data type}
479 *********************************************************
481 A @Doc@ represents a {\em set} of layouts. A @Doc@ with
482 no occurrences of @Union@ or @NoDoc@ represents just one layout.
486 | NilAbove Doc -- text "" $$ x
487 | TextBeside !TextDetails INT Doc -- text s <> x
488 | Nest INT Doc -- nest k x
489 | Union Doc Doc -- ul `union` ur
490 | NoDoc -- The empty set of documents
491 | Beside Doc Bool Doc -- True <=> space between
492 | Above Doc Bool Doc -- True <=> never overlap
494 type RDoc = Doc -- RDoc is a "reduced Doc", guaranteed not to have a top-level Above or Beside
497 reduceDoc :: Doc -> RDoc
498 reduceDoc (Beside p g q) = beside p g (reduceDoc q)
499 reduceDoc (Above p g q) = above p g (reduceDoc q)
503 data TextDetails = Chr {-#UNPACK#-}!Char
505 | PStr FastString -- a hashed string
506 | LStr Addr# Int# -- a '\0'-terminated array of bytes
512 Here are the invariants:
515 The argument of @NilAbove@ is never @Empty@. Therefore
516 a @NilAbove@ occupies at least two lines.
519 The arugment of @TextBeside@ is never @Nest@.
522 The layouts of the two arguments of @Union@ both flatten to the same string.
525 The arguments of @Union@ are either @TextBeside@, or @NilAbove@.
528 The right argument of a union cannot be equivalent to the empty set (@NoDoc@).
529 If the left argument of a union is equivalent to the empty set (@NoDoc@),
530 then the @NoDoc@ appears in the first line.
533 An empty document is always represented by @Empty@.
534 It can't be hidden inside a @Nest@, or a @Union@ of two @Empty@s.
537 The first line of every layout in the left argument of @Union@
538 is longer than the first line of any layout in the right argument.
539 (1) ensures that the left argument has a first line. In view of (3),
540 this invariant means that the right argument must have at least two
545 -- Arg of a NilAbove is always an RDoc
546 nilAbove_ p = LOCAL_ASSERT( ok p ) NilAbove p
551 -- Arg of a TextBeside is always an RDoc
552 textBeside_ s sl p = TextBeside s sl (LOCAL_ASSERT( ok p ) p)
554 ok (Nest _ _) = False
557 -- Arg of Nest is always an RDoc
558 nest_ k p = Nest k (LOCAL_ASSERT( ok p ) p)
563 -- Args of union are always RDocs
564 union_ p q = Union (LOCAL_ASSERT( ok p ) p) (LOCAL_ASSERT( ok q ) q)
566 ok (TextBeside _ _ _) = True
567 ok (NilAbove _) = True
568 ok (Union _ _) = True
573 Notice the difference between
574 * NoDoc (no documents)
575 * Empty (one empty document; no height and no width)
576 * text "" (a document containing the empty string;
577 one line high, but has no width)
581 *********************************************************
583 \subsection{@empty@, @text@, @nest@, @union@}
585 *********************************************************
593 char c = textBeside_ (Chr c) 1# Empty
594 text s = case length s of {IBOX(sl) -> textBeside_ (Str s) sl Empty}
595 ftext s = case lengthFS s of {IBOX(sl) -> textBeside_ (PStr s) sl Empty}
596 ptext (Ptr s) = case strLength (Ptr s) of {IBOX(sl) -> textBeside_ (LStr s sl) sl Empty}
598 -- RULE that turns (text "abc") into (ptext (A# "abc"#)) to avoid the
599 -- intermediate packing/unpacking of the string.
601 "text/str" forall a. text (unpackCString# a) = ptext (Ptr a)
604 nest IBOX(k) p = mkNest k (reduceDoc p) -- Externally callable version
606 -- mkNest checks for Nest's invariant that it doesn't have an Empty inside it
607 mkNest k (Nest k1 p) = mkNest (k PLUS k1) p
608 mkNest k NoDoc = NoDoc
609 mkNest k Empty = Empty
610 mkNest ILIT(0) p = p -- Worth a try!
611 mkNest k p = nest_ k p
613 -- mkUnion checks for an empty document
614 mkUnion Empty q = Empty
615 mkUnion p q = p `union_` q
618 *********************************************************
620 \subsection{Vertical composition @$$@}
622 *********************************************************
626 p $$ q = Above p False q
627 p $+$ q = Above p True q
629 above :: Doc -> Bool -> RDoc -> RDoc
630 above (Above p g1 q1) g2 q2 = above p g1 (above q1 g2 q2)
631 above p@(Beside _ _ _) g q = aboveNest (reduceDoc p) g ILIT(0) (reduceDoc q)
632 above p g q = aboveNest p g ILIT(0) (reduceDoc q)
634 aboveNest :: RDoc -> Bool -> INT -> RDoc -> RDoc
635 -- Specfication: aboveNest p g k q = p $g$ (nest k q)
637 aboveNest NoDoc g k q = NoDoc
638 aboveNest (p1 `Union` p2) g k q = aboveNest p1 g k q `union_`
641 aboveNest Empty g k q = mkNest k q
642 aboveNest (Nest k1 p) g k q = nest_ k1 (aboveNest p g (k MINUS k1) q)
643 -- p can't be Empty, so no need for mkNest
645 aboveNest (NilAbove p) g k q = nilAbove_ (aboveNest p g k q)
646 aboveNest (TextBeside s sl p) g k q = textBeside_ s sl rest
650 Empty -> nilAboveNest g k1 q
651 other -> aboveNest p g k1 q
655 nilAboveNest :: Bool -> INT -> RDoc -> RDoc
656 -- Specification: text s <> nilaboveNest g k q
657 -- = text s <> (text "" $g$ nest k q)
659 nilAboveNest g k Empty = Empty -- Here's why the "text s <>" is in the spec!
660 nilAboveNest g k (Nest k1 q) = nilAboveNest g (k PLUS k1) q
662 nilAboveNest g k q | (not g) && (k GR ILIT(0)) -- No newline if no overlap
663 = textBeside_ (Str (spaces k)) k q
664 | otherwise -- Put them really above
665 = nilAbove_ (mkNest k q)
669 *********************************************************
671 \subsection{Horizontal composition @<>@}
673 *********************************************************
676 p <> q = Beside p False q
677 p <+> q = Beside p True q
679 beside :: Doc -> Bool -> RDoc -> RDoc
680 -- Specification: beside g p q = p <g> q
682 beside NoDoc g q = NoDoc
683 beside (p1 `Union` p2) g q = (beside p1 g q) `union_` (beside p2 g q)
685 beside (Nest k p) g q = nest_ k $! beside p g q -- p non-empty
686 beside p@(Beside p1 g1 q1) g2 q2
687 {- (A `op1` B) `op2` C == A `op1` (B `op2` C) iff op1 == op2
688 [ && (op1 == <> || op1 == <+>) ] -}
689 | g1 == g2 = beside p1 g1 $! beside q1 g2 q2
690 | otherwise = beside (reduceDoc p) g2 q2
691 beside p@(Above _ _ _) g q = let d = reduceDoc p in d `seq` beside d g q
692 beside (NilAbove p) g q = nilAbove_ $! beside p g q
693 beside (TextBeside s sl p) g q = textBeside_ s sl $! rest
696 Empty -> nilBeside g q
697 other -> beside p g q
701 nilBeside :: Bool -> RDoc -> RDoc
702 -- Specification: text "" <> nilBeside g p
705 nilBeside g Empty = Empty -- Hence the text "" in the spec
706 nilBeside g (Nest _ p) = nilBeside g p
707 nilBeside g p | g = textBeside_ space_text ILIT(1) p
711 *********************************************************
713 \subsection{Separate, @sep@, Hughes version}
715 *********************************************************
718 -- Specification: sep ps = oneLiner (hsep ps)
722 sep = sepX True -- Separate with spaces
723 cat = sepX False -- Don't
726 sepX x (p:ps) = sep1 x (reduceDoc p) ILIT(0) ps
729 -- Specification: sep1 g k ys = sep (x : map (nest k) ys)
730 -- = oneLiner (x <g> nest k (hsep ys))
731 -- `union` x $$ nest k (vcat ys)
733 sep1 :: Bool -> RDoc -> INT -> [Doc] -> RDoc
734 sep1 g NoDoc k ys = NoDoc
735 sep1 g (p `Union` q) k ys = sep1 g p k ys
737 (aboveNest q False k (reduceDoc (vcat ys)))
739 sep1 g Empty k ys = mkNest k (sepX g ys)
740 sep1 g (Nest n p) k ys = nest_ n (sep1 g p (k MINUS n) ys)
742 sep1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (reduceDoc (vcat ys)))
743 sep1 g (TextBeside s sl p) k ys = textBeside_ s sl (sepNB g p (k MINUS sl) ys)
745 -- Specification: sepNB p k ys = sep1 (text "" <> p) k ys
746 -- Called when we have already found some text in the first item
747 -- We have to eat up nests
749 sepNB g (Nest _ p) k ys = sepNB g p k ys
751 sepNB g Empty k ys = oneLiner (nilBeside g (reduceDoc rest))
753 nilAboveNest False k (reduceDoc (vcat ys))
756 | otherwise = hcat ys
758 sepNB g p k ys = sep1 g p k ys
761 *********************************************************
765 *********************************************************
774 -- fill (p1:p2:ps) = oneLiner p1 <#> nest (length p1)
775 -- (fill (oneLiner p2 : ps))
780 fill g (p:ps) = fill1 g (reduceDoc p) ILIT(0) ps
783 fill1 :: Bool -> RDoc -> INT -> [Doc] -> Doc
784 fill1 g NoDoc k ys = NoDoc
785 fill1 g (p `Union` q) k ys = fill1 g p k ys
787 (aboveNest q False k (fill g ys))
789 fill1 g Empty k ys = mkNest k (fill g ys)
790 fill1 g (Nest n p) k ys = nest_ n (fill1 g p (k MINUS n) ys)
792 fill1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (fill g ys))
793 fill1 g (TextBeside s sl p) k ys = textBeside_ s sl (fillNB g p (k MINUS sl) ys)
795 fillNB g (Nest _ p) k ys = fillNB g p k ys
796 fillNB g Empty k [] = Empty
797 fillNB g Empty k (y:ys) = nilBeside g (fill1 g (oneLiner (reduceDoc y)) k1 ys)
799 nilAboveNest False k (fill g (y:ys))
801 k1 | g = k MINUS ILIT(1)
804 fillNB g p k ys = fill1 g p k ys
808 *********************************************************
810 \subsection{Selecting the best layout}
812 *********************************************************
815 best :: Int -- Line length
816 -> Int -- Ribbon length
818 -> RDoc -- No unions in here!
820 best IBOX(w) IBOX(r) p
823 get :: INT -- (Remaining) width of line
827 get w (NilAbove p) = nilAbove_ (get w p)
828 get w (TextBeside s sl p) = textBeside_ s sl (get1 w sl p)
829 get w (Nest k p) = nest_ k (get (w MINUS k) p)
830 get w (p `Union` q) = nicest w r (get w p) (get w q)
832 get1 :: INT -- (Remaining) width of line
833 -> INT -- Amount of first line already eaten up
834 -> Doc -- This is an argument to TextBeside => eat Nests
835 -> Doc -- No unions in here!
837 get1 w sl Empty = Empty
838 get1 w sl NoDoc = NoDoc
839 get1 w sl (NilAbove p) = nilAbove_ (get (w MINUS sl) p)
840 get1 w sl (TextBeside t tl p) = textBeside_ t tl (get1 w (sl PLUS tl) p)
841 get1 w sl (Nest k p) = get1 w sl p
842 get1 w sl (p `Union` q) = nicest1 w r sl (get1 w sl p)
845 nicest w r p q = nicest1 w r ILIT(0) p q
846 nicest1 w r sl p q | fits ((w `minn` r) MINUS sl) p = p
849 fits :: INT -- Space available
851 -> Bool -- True if *first line* of Doc fits in space available
853 fits n p | n LT ILIT(0) = False
856 fits n (NilAbove _) = True
857 fits n (TextBeside _ sl p) = fits (n MINUS sl) p
859 minn x y | x LT y = x
863 @first@ and @nonEmptySet@ are similar to @nicest@ and @fits@, only simpler.
864 @first@ returns its first argument if it is non-empty, otherwise its second.
867 first p q | nonEmptySet p = p
870 nonEmptySet NoDoc = False
871 nonEmptySet (p `Union` q) = True
872 nonEmptySet Empty = True
873 nonEmptySet (NilAbove p) = True -- NoDoc always in first line
874 nonEmptySet (TextBeside _ _ p) = nonEmptySet p
875 nonEmptySet (Nest _ p) = nonEmptySet p
878 @oneLiner@ returns the one-line members of the given set of @Doc@s.
881 oneLiner :: Doc -> Doc
882 oneLiner NoDoc = NoDoc
883 oneLiner Empty = Empty
884 oneLiner (NilAbove p) = NoDoc
885 oneLiner (TextBeside s sl p) = textBeside_ s sl (oneLiner p)
886 oneLiner (Nest k p) = nest_ k (oneLiner p)
887 oneLiner (p `Union` q) = oneLiner p
892 *********************************************************
894 \subsection{Displaying the best layout}
896 *********************************************************
901 renderStyle Style{mode, lineLength, ribbonsPerLine} doc
902 = fullRender mode lineLength ribbonsPerLine doc ""
905 render doc = showDocWith PageMode doc
906 showDoc doc rest = showDocWithAppend PageMode doc rest
908 showDocWithAppend :: Mode -> Doc -> String -> String
909 showDocWithAppend mode doc rest = fullRender mode 100 1.5 string_txt rest doc
911 showDocWith :: Mode -> Doc -> String
912 showDocWith mode doc = showDocWithAppend mode doc ""
914 string_txt (Chr c) s = c:s
915 string_txt (Str s1) s2 = s1 ++ s2
916 string_txt (PStr s1) s2 = unpackFS s1 ++ s2
917 string_txt (LStr s1 _) s2 = unpackLitString s1 ++ s2
919 unpackLitString addr =
923 | ch `eqChar#` '\0'# = []
924 | otherwise = C# ch : unpack (nh +# 1#)
926 ch = indexCharOffAddr# addr nh
931 fullRender OneLineMode _ _ txt end doc
932 = lay (reduceDoc doc)
934 lay NoDoc = cant_fail
935 lay (Union p q) = (lay q) -- Second arg can't be NoDoc
936 lay (Nest k p) = lay p
938 lay (NilAbove p) = space_text `txt` lay p -- NoDoc always on first line
939 lay (TextBeside s sl p) = s `txt` lay p
941 fullRender LeftMode _ _ txt end doc
942 = lay (reduceDoc doc)
944 lay NoDoc = cant_fail
945 lay (Union p q) = lay (first p q)
946 lay (Nest k p) = lay p
948 lay (NilAbove p) = nl_text `txt` lay p -- NoDoc always on first line
949 lay (TextBeside s sl p) = s `txt` lay p
951 fullRender mode line_length ribbons_per_line txt end doc
952 = display mode line_length ribbon_length txt end best_doc
954 best_doc = best hacked_line_length ribbon_length (reduceDoc doc)
956 hacked_line_length, ribbon_length :: Int
957 ribbon_length = round (fromIntegral line_length / ribbons_per_line)
958 hacked_line_length = case mode of { ZigZagMode -> MAXINT; other -> line_length }
960 display mode IBOX(page_width) IBOX(ribbon_width) txt end doc
961 = case page_width MINUS ribbon_width of { gap_width ->
962 case gap_width DIV ILIT(2) of { shift ->
964 lay k (Nest k1 p) = lay (k PLUS k1) p
967 lay k (NilAbove p) = nl_text `txt` lay k p
969 lay k (TextBeside s sl p)
971 ZigZagMode | k GREQ gap_width
973 Str (multi_ch shift '/') `txt` (
975 lay1 (k MINUS shift) s sl p)))
979 Str (multi_ch shift '\\') `txt` (
981 lay1 (k PLUS shift) s sl p )))
983 other -> lay1 k s sl p
985 lay1 k s sl p = Str (indent k) `txt` (s `txt` lay2 (k PLUS sl) p)
987 lay2 k (NilAbove p) = nl_text `txt` lay k p
988 lay2 k (TextBeside s sl p) = s `txt` (lay2 (k PLUS sl) p)
989 lay2 k (Nest _ p) = lay2 k p
995 cant_fail = error "easy_display: NoDoc"
997 indent n | n GREQ ILIT(8) = '\t' : indent (n MINUS ILIT(8))
998 | otherwise = spaces n
1000 multi_ch n ch | n LTEQ ILIT(0) = ""
1001 | otherwise = ch : multi_ch (n MINUS ILIT(1)) ch
1003 spaces n | n LTEQ ILIT(0) = ""
1004 | otherwise = ' ' : spaces (n MINUS ILIT(1))
1008 pprCols = (120 :: Int) -- could make configurable
1010 printDoc :: Mode -> Handle -> Doc -> IO ()
1011 printDoc LeftMode hdl doc
1012 = do { printLeftRender hdl doc; hFlush hdl }
1013 printDoc mode hdl doc
1014 = do { fullRender mode pprCols 1.5 put done doc ;
1017 put (Chr c) next = hPutChar hdl c >> next
1018 put (Str s) next = hPutStr hdl s >> next
1019 put (PStr s) next = hPutFS hdl s >> next
1020 put (LStr s l) next = hPutLitString hdl s l >> next
1022 done = hPutChar hdl '\n'
1024 -- some versions of hPutBuf will barf if the length is zero
1025 hPutLitString handle a# 0# = return ()
1026 hPutLitString handle a# l#
1027 = hPutBuf handle (Ptr a#) (I# l#)
1029 -- Printing output in LeftMode is performance critical: it's used when
1030 -- dumping C and assembly output, so we allow ourselves a few dirty
1033 -- (1) we specialise fullRender for LeftMode with IO output.
1035 -- (2) we add a layer of buffering on top of Handles. Handles
1036 -- don't perform well with lots of hPutChars, which is mostly
1037 -- what we're doing here, because Handles have to be thread-safe
1038 -- and async exception-safe. We only have a single thread and don't
1039 -- care about exceptions, so we add a layer of fast buffering
1040 -- over the Handle interface.
1042 -- (3) a few hacks in layLeft below to convince GHC to generate the right
1045 printLeftRender :: Handle -> Doc -> IO ()
1046 printLeftRender hdl doc = do
1047 b <- newBufHandle hdl
1048 layLeft b (reduceDoc doc)
1051 -- HACK ALERT! the "return () >>" below convinces GHC to eta-expand
1052 -- this function with the IO state lambda. Otherwise we end up with
1053 -- closures in all the case branches.
1054 layLeft b _ | b `seq` False = undefined -- make it strict in b
1055 layLeft b NoDoc = cant_fail
1056 layLeft b (Union p q) = return () >> layLeft b (first p q)
1057 layLeft b (Nest k p) = return () >> layLeft b p
1058 layLeft b Empty = bPutChar b '\n'
1059 layLeft b (NilAbove p) = bPutChar b '\n' >> layLeft b p
1060 layLeft b (TextBeside s sl p) = put b s >> layLeft b p
1062 put b _ | b `seq` False = undefined
1063 put b (Chr c) = bPutChar b c
1064 put b (Str s) = bPutStr b s
1065 put b (PStr s) = bPutFS b s
1066 put b (LStr s l) = bPutLitString b s l