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 2.0 24 April 1997
15 * Made empty into a left unit for <> as well as a right unit;
16 it is also now true that
18 which wasn't true before.
20 * Fixed an obscure bug in sep that occassionally gave very wierd behaviour
24 * Corrected and tidied up the laws and invariants
26 ======================================================================
27 Relative to John's original paper, there are the following new features:
29 1. There's an empty document, "empty". It's a left and right unit for
30 both <> and $$, and anywhere in the argument list for
31 sep, hcat, hsep, vcat, fcat etc.
33 It is Really Useful in practice.
35 2. There is a paragraph-fill combinator, fsep, that's much like sep,
36 only it keeps fitting things on one line until itc can't fit any more.
38 3. Some random useful extra combinators are provided.
39 <+> puts its arguments beside each other with a space between them,
40 unless either argument is empty in which case it returns the other
43 hcat is a list version of <>
44 hsep is a list version of <+>
45 vcat is a list version of $$
47 sep (separate) is either like hsep or like vcat, depending on what fits
49 cat is behaves like sep, but it uses <> for horizontal conposition
50 fcat is behaves like fsep, but it uses <> for horizontal conposition
52 These new ones do the obvious things:
53 char, semi, comma, colon, space,
54 parens, brackets, braces,
57 4. The "above" combinator, $$, now overlaps its two arguments if the
58 last line of the top argument stops before the first line of the second begins.
59 For example: text "hi" $$ nest 5 "there"
66 There are two places this is really useful
68 a) When making labelled blocks, like this:
70 Right -> code for right
72 code for longlonglonglabel
73 The block is on the same line as the label if the label is
74 short, but on the next line otherwise.
76 b) When laying out lists like this:
81 which some people like. But if the list fits on one line
82 you want [first, second, third]. You can't do this with
83 John's original combinators, but it's quite easy with the
86 The combinator $+$ gives the original "never-overlap" behaviour.
88 5. Several different renderers are provided:
90 * one that uses cut-marks to avoid deeply-nested documents
91 simply piling up in the right-hand margin
92 * one that ignores indentation (fewer chars output; good for machines)
93 * one that ignores indentation and newlines (ditto, only more so)
95 6. Numerous implementation tidy-ups
96 Use of unboxed data types to speed up the implementation
103 Mode(..), TextDetails(..),
108 int, integer, float, double, rational,
109 parens, brackets, braces, quotes, doubleQuotes,
110 semi, comma, colon, space, equals,
111 lparen, rparen, lbrack, rbrack, lbrace, rbrace,
113 (<>), (<+>), hcat, hsep,
120 -- renderStyle, -- Haskell 1.3 only
124 #include "HsVersions.h"
129 -- Don't import Util( assertPanic ) because it makes a loop in the module structure
138 *********************************************************
140 \subsection{CPP magic so that we can compile with both GHC and Hugs}
142 *********************************************************
144 The library uses unboxed types to get a bit more speed, but these CPP macros
145 allow you to use either GHC or Hugs. To get GHC, just set the CPP variable
150 #if defined(__GLASGOW_HASKELL__)
155 -- Disable ASSERT checks; they are expensive!
156 #define LOCAL_ASSERT(x)
160 #define NEGATE negateInt#
165 #define DIV `quotInt#`
168 #if __GLASGOW_HASKELL__ >= 202
171 #define MAXINT maxBound
176 #define MAXINT maxInt
184 #define LOCAL_ASSERT(x)
189 #define NEGATE negate
198 #define MAXINT maxBound
205 *********************************************************
207 \subsection{The interface}
209 *********************************************************
211 The primitive @Doc@ values
215 text :: String -> Doc
218 semi, comma, colon, space, equals :: Doc
219 lparen, rparen, lbrack, rbrack, lbrace, rbrace :: Doc
221 parens, brackets, braces :: Doc -> Doc
222 quotes, doubleQuotes :: Doc -> Doc
225 integer :: Integer -> Doc
226 float :: Float -> Doc
227 double :: Double -> Doc
228 rational :: Rational -> Doc
231 Combining @Doc@ values
234 (<>) :: Doc -> Doc -> Doc -- Beside
235 hcat :: [Doc] -> Doc -- List version of <>
236 (<+>) :: Doc -> Doc -> Doc -- Beside, separated by space
237 hsep :: [Doc] -> Doc -- List version of <+>
239 ($$) :: Doc -> Doc -> Doc -- Above; if there is no
240 -- overlap it "dovetails" the two
241 vcat :: [Doc] -> Doc -- List version of $$
243 cat :: [Doc] -> Doc -- Either hcat or vcat
244 sep :: [Doc] -> Doc -- Either hsep or vcat
245 fcat :: [Doc] -> Doc -- ``Paragraph fill'' version of cat
246 fsep :: [Doc] -> Doc -- ``Paragraph fill'' version of sep
248 nest :: Int -> Doc -> Doc -- Nested
254 hang :: Doc -> Int -> Doc -> Doc
255 punctuate :: Doc -> [Doc] -> [Doc] -- punctuate p [d1, ... dn] = [d1 <> p, d2 <> p, ... dn-1 <> p, dn]
258 Displaying @Doc@ values.
261 instance SHOW Doc where
262 showsPrec prec doc cont = showDoc doc cont
264 render :: Doc -> String -- Uses default style
266 -> Int -- Line length
267 -> Float -- Ribbons per line
268 -> (TextDetails -> a -> a) -- What to do with text
269 -> a -- What to do at the end
273 {- When we start using 1.3
274 renderStyle :: Style -> Doc -> String
275 data Style = Style { lineLength :: Int, -- In chars
276 ribbonsPerLine :: Float, -- Ratio of ribbon length to line length
279 style :: Style -- The default style
280 style = Style { lineLength = 100, ribbonsPerLine = 2.5, mode = PageMode }
283 data Mode = PageMode -- Normal
284 | ZigZagMode -- With zig-zag cuts
285 | LeftMode -- No indentation, infinitely long lines
286 | OneLineMode -- All on one line
291 *********************************************************
293 \subsection{The @Doc@ calculus}
295 *********************************************************
297 The @Doc@ combinators satisfy the following laws:
301 <a1> (x $$ y) $$ z = x $$ (y $$ z)
309 <b1> (x <> y) <> z = x <> (y <> z)
310 <b2> empty <> x = empty
317 <t1> text s <> text t = text (s++t)
318 <t2> text "" <> x = x, if x non-empty
323 <n2> nest k (nest k' x) = nest (k+k') x
324 <n3> nest k (x <> y) = nest k z <> nest k y
325 <n4> nest k (x $$ y) = nest k x $$ nest k y
326 <n5> nest k empty = empty
327 <n6> x <> nest k y = x <> y, if x non-empty
329 ** Note the side condition on <n6>! It is this that
330 ** makes it OK for empty to be a left unit for <>.
334 <m1> (text s <> x) $$ y = text s <> ((text "" <> x)) $$
337 <m2> (x $$ y) <> z = x $$ (y <> z)
341 Laws for list versions
342 ~~~~~~~~~~~~~~~~~~~~~~
343 <l1> sep (ps++[empty]++qs) = sep (ps ++ qs)
344 ...ditto hsep, hcat, vcat, fill...
346 <l2> nest k (sep ps) = sep (map (nest k) ps)
347 ...ditto hsep, hcat, vcat, fill...
351 <o1> oneLiner (nest k p) = nest k (oneLiner p)
352 <o2> oneLiner (x <> y) = oneLiner x <> oneLiner y
356 You might think that the following verion of <m1> would
359 <3 NO> (text s <> x) $$ y = text s <> ((empty <> x)) $$
362 But it doesn't work, for if x=empty, we would have
364 text s $$ y = text s <> (empty $$ nest (-length s) y)
365 = text s <> nest (-length s) y
370 *********************************************************
372 \subsection{Simple derived definitions}
374 *********************************************************
389 int n = text (show n)
390 integer n = text (show n)
391 float n = text (show n)
392 double n = text (show n)
393 --ORIG: rational n = text (show n)
394 rational n = text (show (fromRationalX n)) -- _showRational 30 n)
396 quotes p = char '`' <> p <> char '\''
397 doubleQuotes p = char '"' <> p <> char '"'
398 parens p = char '(' <> p <> char ')'
399 brackets p = char '[' <> p <> char ']'
400 braces p = char '{' <> p <> char '}'
403 hcat = foldr (<>) empty
404 hsep = foldr (<+>) empty
405 vcat = foldr ($$) empty
407 hang d1 n d2 = sep [d1, nest n d2]
410 punctuate p (d:ds) = go d ds
413 go d (e:es) = (d <> p) : go e es
417 *********************************************************
419 \subsection{The @Doc@ data type}
421 *********************************************************
423 A @Doc@ represents a {\em set} of layouts. A @Doc@ with
424 no occurrences of @Union@ or @NoDoc@ represents just one layout.
428 | NilAbove Doc -- text "" $$ x
429 | TextBeside TextDetails INT Doc -- text s <> x
430 | Nest INT Doc -- nest k x
431 | Union Doc Doc -- ul `union` ur
432 | NoDoc -- The empty set of documents
433 | Beside Doc Bool Doc -- True <=> space between
434 | Above Doc Bool Doc -- True <=> never overlap
436 type RDoc = Doc -- RDoc is a "reduced Doc", guaranteed not to have a top-level Above or Beside
439 reduceDoc :: Doc -> RDoc
440 reduceDoc (Beside p g q) = beside p g (reduceDoc q)
441 reduceDoc (Above p g q) = above p g (reduceDoc q)
445 data TextDetails = Chr Char
452 Here are the invariants:
455 The argument of @NilAbove@ is never @Empty@. Therefore
456 a @NilAbove@ occupies at least two lines.
459 The arugment of @TextBeside@ is never @Nest@.
462 The layouts of the two arguments of @Union@ both flatten to the same string.
465 The arguments of @Union@ are either @TextBeside@, or @NilAbove@.
468 The right argument of a union cannot be equivalent to the empty set (@NoDoc@).
469 If the left argument of a union is equivalent to the empty set (@NoDoc@),
470 then the @NoDoc@ appears in the first line.
473 An empty document is always represented by @Empty@.
474 It can't be hidden inside a @Nest@, or a @Union@ of two @Empty@s.
477 The first line of every layout in the left argument of @Union@
478 is longer than the first line of any layout in the right argument.
479 (1) ensures that the left argument has a first line. In view of (3),
480 this invariant means that the right argument must have at least two
485 -- Arg of a NilAbove is always an RDoc
486 nilAbove_ p = LOCAL_ASSERT( ok p ) NilAbove p
491 -- Arg of a TextBeside is always an RDoc
492 textBeside_ s sl p = TextBeside s sl (LOCAL_ASSERT( ok p ) p)
494 ok (Nest _ _) = False
497 -- Arg of Nest is always an RDoc
498 nest_ k p = Nest k (LOCAL_ASSERT( ok p ) p)
503 -- Args of union are always RDocs
504 union_ p q = Union (LOCAL_ASSERT( ok p ) p) (LOCAL_ASSERT( ok q ) q)
506 ok (TextBeside _ _ _) = True
507 ok (NilAbove _) = True
508 ok (Union _ _) = True
513 Notice the difference between
514 * NoDoc (no documents)
515 * Empty (one empty document; no height and no width)
516 * text "" (a document containing the empty string;
517 one line high, but has no width)
521 *********************************************************
523 \subsection{@empty@, @text@, @nest@, @union@}
525 *********************************************************
530 char c = textBeside_ (Chr c) 1# Empty
531 text s = case length s of {IBOX(sl) -> textBeside_ (Str s) sl Empty}
532 ptext s = case _LENGTH_ s of {IBOX(sl) -> textBeside_ (PStr s) sl Empty}
534 nest IBOX(k) p = mkNest k (reduceDoc p) -- Externally callable version
536 -- mkNest checks for Nest's invariant that it doesn't have an Empty inside it
537 mkNest k (Nest k1 p) = mkNest (k PLUS k1) p
538 mkNest k NoDoc = NoDoc
539 mkNest k Empty = Empty
540 mkNest ILIT(0) p = p -- Worth a try!
541 mkNest k p = nest_ k p
543 -- mkUnion checks for an empty document
544 mkUnion Empty q = Empty
545 mkUnion p q = p `union_` q
548 *********************************************************
550 \subsection{Vertical composition @$$@}
552 *********************************************************
556 p $$ q = Above p False q
557 p $+$ q = Above p True q
559 above :: Doc -> Bool -> RDoc -> RDoc
560 above (Above p g1 q1) g2 q2 = above p g1 (above q1 g2 q2)
561 above p@(Beside _ _ _) g q = aboveNest (reduceDoc p) g ILIT(0) (reduceDoc q)
562 above p g q = aboveNest p g ILIT(0) (reduceDoc q)
564 aboveNest :: RDoc -> Bool -> INT -> RDoc -> RDoc
565 -- Specfication: aboveNest p g k q = p $g$ (nest k q)
567 aboveNest NoDoc g k q = NoDoc
568 aboveNest (p1 `Union` p2) g k q = aboveNest p1 g k q `union_`
571 aboveNest Empty g k q = mkNest k q
572 aboveNest (Nest k1 p) g k q = nest_ k1 (aboveNest p g (k MINUS k1) q)
573 -- p can't be Empty, so no need for mkNest
575 aboveNest (NilAbove p) g k q = nilAbove_ (aboveNest p g k q)
576 aboveNest (TextBeside s sl p) g k q = textBeside_ s sl rest
580 Empty -> nilAboveNest g k1 q
581 other -> aboveNest p g k1 q
585 nilAboveNest :: Bool -> INT -> RDoc -> RDoc
586 -- Specification: text s <> nilaboveNest g k q
587 -- = text s <> (text "" $g$ nest k q)
589 nilAboveNest g k Empty = Empty -- Here's why the "text s <>" is in the spec!
590 nilAboveNest g k (Nest k1 q) = nilAboveNest g (k PLUS k1) q
592 nilAboveNest g k q | (not g) && (k GR ILIT(0)) -- No newline if no overlap
593 = textBeside_ (Str (spaces k)) k q
594 | otherwise -- Put them really above
595 = nilAbove_ (mkNest k q)
599 *********************************************************
601 \subsection{Horizontal composition @<>@}
603 *********************************************************
606 p <> q = Beside p False q
607 p <+> q = Beside p True q
609 beside :: Doc -> Bool -> RDoc -> RDoc
610 -- Specification: beside g p q = p <g> q
612 beside NoDoc g q = NoDoc
613 beside (p1 `Union` p2) g q = (beside p1 g q) `union_` (beside p2 g q)
615 beside (Nest k p) g q = nest_ k (beside p g q) -- p non-empty
616 beside p@(Beside p1 g1 q1) g2 q2
617 {- (A `op1` B) `op2` C == A `op1` (B `op2` C) iff op1 == op2
618 [ && (op1 == <> || op1 == <+>) ] -}
619 | g1 == g2 = beside p1 g1 (beside q1 g2 q2)
620 | otherwise = beside (reduceDoc p) g2 q2
621 beside p@(Above _ _ _) g q = beside (reduceDoc p) g q
622 beside (NilAbove p) g q = nilAbove_ (beside p g q)
623 beside (TextBeside s sl p) g q = textBeside_ s sl rest
626 Empty -> nilBeside g q
627 other -> beside p g q
631 nilBeside :: Bool -> RDoc -> RDoc
632 -- Specification: text "" <> nilBeside g p
635 nilBeside g Empty = Empty -- Hence the text "" in the spec
636 nilBeside g (Nest _ p) = nilBeside g p
637 nilBeside g p | g = textBeside_ space_text ILIT(1) p
641 *********************************************************
643 \subsection{Separate, @sep@, Hughes version}
645 *********************************************************
648 -- Specification: sep ps = oneLiner (hsep ps)
652 sep = sepX True -- Separate with spaces
653 cat = sepX False -- Don't
656 sepX x (p:ps) = sep1 x (reduceDoc p) ILIT(0) ps
659 -- Specification: sep1 g k ys = sep (x : map (nest k) ys)
660 -- = oneLiner (x <g> nest k (hsep ys))
661 -- `union` x $$ nest k (vcat ys)
663 sep1 :: Bool -> RDoc -> INT -> [Doc] -> RDoc
664 sep1 g NoDoc k ys = NoDoc
665 sep1 g (p `Union` q) k ys = sep1 g p k ys
667 (aboveNest q False k (reduceDoc (vcat ys)))
669 sep1 g Empty k ys = mkNest k (sepX g ys)
670 sep1 g (Nest n p) k ys = nest_ n (sep1 g p (k MINUS n) ys)
672 sep1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (reduceDoc (vcat ys)))
673 sep1 g (TextBeside s sl p) k ys = textBeside_ s sl (sepNB g p (k MINUS sl) ys)
675 -- Specification: sepNB p k ys = sep1 (text "" <> p) k ys
676 -- Called when we have already found some text in the first item
677 -- We have to eat up nests
679 sepNB g (Nest _ p) k ys = sepNB g p k ys
681 sepNB g Empty k ys = oneLiner (nilBeside g (reduceDoc rest))
683 nilAboveNest False k (reduceDoc (vcat ys))
686 | otherwise = hcat ys
688 sepNB g p k ys = sep1 g p k ys
691 *********************************************************
695 *********************************************************
704 -- fill (p1:p2:ps) = oneLiner p1 <#> nest (length p1)
705 -- (fill (oneLiner p2 : ps))
710 fill g (p:ps) = fill1 g (reduceDoc p) ILIT(0) ps
713 fill1 :: Bool -> RDoc -> INT -> [Doc] -> Doc
714 fill1 g NoDoc k ys = NoDoc
715 fill1 g (p `Union` q) k ys = fill1 g p k ys
717 (aboveNest q False k (fill g ys))
719 fill1 g Empty k ys = mkNest k (fill g ys)
720 fill1 g (Nest n p) k ys = nest_ n (fill1 g p (k MINUS n) ys)
722 fill1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (fill g ys))
723 fill1 g (TextBeside s sl p) k ys = textBeside_ s sl (fillNB g p (k MINUS sl) ys)
725 fillNB g (Nest _ p) k ys = fillNB g p k ys
726 fillNB g Empty k [] = Empty
727 fillNB g Empty k (y:ys) = nilBeside g (fill1 g (oneLiner (reduceDoc y)) k1 ys)
729 nilAboveNest False k (fill g (y:ys))
731 k1 | g = k MINUS ILIT(1)
734 fillNB g p k ys = fill1 g p k ys
738 *********************************************************
740 \subsection{Selecting the best layout}
742 *********************************************************
746 -> Int -- Line length
747 -> Int -- Ribbon length
749 -> RDoc -- No unions in here!
751 best OneLineMode IBOX(w) IBOX(r) p
756 get (NilAbove p) = nilAbove_ (get p)
757 get (TextBeside s sl p) = textBeside_ s sl (get p)
758 get (Nest k p) = get p -- Elide nest
759 get (p `Union` q) = first (get p) (get q)
761 best mode IBOX(w) IBOX(r) p
764 get :: INT -- (Remaining) width of line
768 get w (NilAbove p) = nilAbove_ (get w p)
769 get w (TextBeside s sl p) = textBeside_ s sl (get1 w sl p)
770 get w (Nest k p) = nest_ k (get (w MINUS k) p)
771 get w (p `Union` q) = nicest w r (get w p) (get w q)
773 get1 :: INT -- (Remaining) width of line
774 -> INT -- Amount of first line already eaten up
775 -> Doc -- This is an argument to TextBeside => eat Nests
776 -> Doc -- No unions in here!
778 get1 w sl Empty = Empty
779 get1 w sl NoDoc = NoDoc
780 get1 w sl (NilAbove p) = nilAbove_ (get (w MINUS sl) p)
781 get1 w sl (TextBeside t tl p) = textBeside_ t tl (get1 w (sl PLUS tl) p)
782 get1 w sl (Nest k p) = get1 w sl p
783 get1 w sl (p `Union` q) = nicest1 w r sl (get1 w sl p)
786 nicest w r p q = nicest1 w r ILIT(0) p q
787 nicest1 w r sl p q | fits ((w `minn` r) MINUS sl) p = p
790 fits :: INT -- Space available
792 -> Bool -- True if *first line* of Doc fits in space available
794 fits n p | n LT ILIT(0) = False
797 fits n (NilAbove _) = True
798 fits n (TextBeside _ sl p) = fits (n MINUS sl) p
800 minn x y | x LT y = x
804 @first@ and @nonEmptySet@ are similar to @nicest@ and @fits@, only simpler.
805 @first@ returns its first argument if it is non-empty, otherwise its second.
808 first p q | nonEmptySet p = p
811 nonEmptySet NoDoc = False
812 nonEmptySet (p `Union` q) = True
813 nonEmptySet Empty = True
814 nonEmptySet (NilAbove p) = True -- NoDoc always in first line
815 nonEmptySet (TextBeside _ _ p) = nonEmptySet p
816 nonEmptySet (Nest _ p) = nonEmptySet p
819 @oneLiner@ returns the one-line members of the given set of @Doc@s.
822 oneLiner :: Doc -> Doc
823 oneLiner NoDoc = NoDoc
824 oneLiner Empty = Empty
825 oneLiner (NilAbove p) = NoDoc
826 oneLiner (TextBeside s sl p) = textBeside_ s sl (oneLiner p)
827 oneLiner (Nest k p) = nest_ k (oneLiner p)
828 oneLiner (p `Union` q) = oneLiner p
833 *********************************************************
835 \subsection{Displaying the best layout}
837 *********************************************************
842 renderStyle Style{mode, lineLength, ribbonsPerLine} doc
843 = fullRender mode lineLength ribbonsPerLine doc ""
846 render doc = showDoc doc ""
847 showDoc doc rest = fullRender PageMode 100 1.5 string_txt rest doc
849 string_txt (Chr c) s = c:s
850 string_txt (Str s1) s2 = s1 ++ s2
851 string_txt (PStr s1) s2 = _UNPK_ s1 ++ s2
856 fullRender OneLineMode _ _ txt end doc = easy_display space_text txt end (reduceDoc doc)
857 fullRender LeftMode _ _ txt end doc = easy_display nl_text txt end (reduceDoc doc)
859 fullRender mode line_length ribbons_per_line txt end doc
860 = display mode line_length ribbon_length txt end best_doc
862 best_doc = best mode hacked_line_length ribbon_length (reduceDoc doc)
864 hacked_line_length, ribbon_length :: Int
865 ribbon_length = round (fromInt line_length / ribbons_per_line)
866 hacked_line_length = case mode of { ZigZagMode -> MAXINT; other -> line_length }
868 display mode IBOX(page_width) IBOX(ribbon_width) txt end doc
869 = case page_width MINUS ribbon_width of { gap_width ->
870 case gap_width DIV ILIT(2) of { shift ->
872 lay k (Nest k1 p) = lay (k PLUS k1) p
875 lay k (NilAbove p) = nl_text `txt` lay k p
877 lay k (TextBeside s sl p)
879 ZigZagMode | k GREQ gap_width
881 Str (multi_ch shift '/') `txt` (
883 lay1 (k MINUS shift) s sl p)))
887 Str (multi_ch shift '\\') `txt` (
889 lay1 (k PLUS shift) s sl p )))
891 other -> lay1 k s sl p
893 lay1 k s sl p = Str (indent k) `txt` (s `txt` lay2 (k PLUS sl) p)
895 lay2 k (NilAbove p) = nl_text `txt` lay k p
896 lay2 k (TextBeside s sl p) = s `txt` (lay2 (k PLUS sl) p)
897 lay2 k (Nest _ p) = lay2 k p
903 cant_fail = error "easy_display: NoDoc"
904 easy_display nl_text txt end doc
907 lay NoDoc no_doc = no_doc
908 lay (Union p q) no_doc = {- lay p -} (lay q cant_fail) -- Second arg can't be NoDoc
909 lay (Nest k p) no_doc = lay p no_doc
910 lay Empty no_doc = end
911 lay (NilAbove p) no_doc = nl_text `txt` lay p cant_fail -- NoDoc always on first line
912 lay (TextBeside s sl p) no_doc = s `txt` lay p no_doc
914 indent n | n GREQ ILIT(8) = '\t' : indent (n MINUS ILIT(8))
915 | otherwise = spaces n
917 multi_ch ILIT(0) ch = ""
918 multi_ch n ch = ch : multi_ch (n MINUS ILIT(1)) ch
921 spaces n = ' ' : spaces (n MINUS ILIT(1))
924 Doesn't really belong here..
926 -----------------------------------
929 fromRationalX :: (RealFloat a) => Rational -> a
933 h = ceiling (huge `asTypeOf` x)
934 b = toInteger (floatRadix x)
937 let d = denominator r'
940 let e = integerLogBase b (d `div` h) + 1
941 in fromRat (e0-e) (n % (d `div` (b^e)))
942 else if abs n > h then
943 let e = integerLogBase b (abs n `div` h) + 1
944 in fromRat (e0+e) ((n `div` (b^e)) % d)
946 scaleFloat e0 (fromRational r')
949 -- Compute the discrete log of i in base b.
950 -- Simplest way would be just divide i by b until it's smaller then b, but that would
951 -- be very slow! We are just slightly more clever.
952 integerLogBase :: Integer -> Integer -> Int
957 -- Try squaring the base first to cut down the number of divisions.
958 let l = 2 * integerLogBase (b*b) i
960 doDiv :: Integer -> Int -> Int
961 doDiv j k = if j < b then k else doDiv (j `div` b) (k+1)
963 doDiv (i `div` (b^l)) l
968 -- Compute smallest and largest floating point values.
970 tiny :: (RealFloat a) => a
972 let (l, _) = floatRange x
973 x = encodeFloat 1 (l-1)
977 huge :: (RealFloat a) => a
979 let (_, u) = floatRange x
981 x = encodeFloat (floatRadix x ^ d - 1) (u - d)