[project @ 2002-07-25 14:14:36 by simonmar]
[packages/random.git] / Text / PrettyPrint / HughesPJ.hs
1 -----------------------------------------------------------------------------
2 -- |
3 -- Module : Text.PrettyPrint.HughesPJ
4 -- Copyright : (c) The University of Glasgow 2001
5 -- License : BSD-style (see the file libraries/base/LICENSE)
6 --
7 -- Maintainer : libraries@haskell.org
8 -- Stability : provisional
9 -- Portability : portable
10 --
11 -- John Hughes's and Simon Peyton Jones's Pretty Printer Combinators
12 --
13 -- Based on /The Design of a Pretty-printing Library/
14 -- in Advanced Functional Programming,
15 -- Johan Jeuring and Erik Meijer (eds), LNCS 925
16 -- <http://www.cs.chalmers.se/~rjmh/Papers/pretty.ps>
17 --
18 -- Heavily modified by Simon Peyton Jones, Dec 96
19 --
20 -----------------------------------------------------------------------------
21
22 {-
23 Version 3.0 28 May 1997
24 * Cured massive performance bug. If you write
25
26 foldl <> empty (map (text.show) [1..10000])
27
28 you get quadratic behaviour with V2.0. Why? For just the same
29 reason as you get quadratic behaviour with left-associated (++)
30 chains.
31
32 This is really bad news. One thing a pretty-printer abstraction
33 should certainly guarantee is insensivity to associativity. It
34 matters: suddenly GHC's compilation times went up by a factor of
35 100 when I switched to the new pretty printer.
36
37 I fixed it with a bit of a hack (because I wanted to get GHC back
38 on the road). I added two new constructors to the Doc type, Above
39 and Beside:
40
41 <> = Beside
42 $$ = Above
43
44 Then, where I need to get to a "TextBeside" or "NilAbove" form I
45 "force" the Doc to squeeze out these suspended calls to Beside and
46 Above; but in so doing I re-associate. It's quite simple, but I'm
47 not satisfied that I've done the best possible job. I'll send you
48 the code if you are interested.
49
50 * Added new exports:
51 punctuate, hang
52 int, integer, float, double, rational,
53 lparen, rparen, lbrack, rbrack, lbrace, rbrace,
54
55 * fullRender's type signature has changed. Rather than producing a
56 string it now takes an extra couple of arguments that tells it how
57 to glue fragments of output together:
58
59 fullRender :: Mode
60 -> Int -- Line length
61 -> Float -- Ribbons per line
62 -> (TextDetails -> a -> a) -- What to do with text
63 -> a -- What to do at the end
64 -> Doc
65 -> a -- Result
66
67 The "fragments" are encapsulated in the TextDetails data type:
68
69 data TextDetails = Chr Char
70 | Str String
71 | PStr FAST_STRING
72
73 The Chr and Str constructors are obvious enough. The PStr
74 constructor has a packed string (FAST_STRING) inside it. It's
75 generated by using the new "ptext" export.
76
77 An advantage of this new setup is that you can get the renderer to
78 do output directly (by passing in a function of type (TextDetails
79 -> IO () -> IO ()), rather than producing a string that you then
80 print.
81
82
83 Version 2.0 24 April 1997
84 * Made empty into a left unit for <> as well as a right unit;
85 it is also now true that
86 nest k empty = empty
87 which wasn't true before.
88
89 * Fixed an obscure bug in sep that occassionally gave very weird behaviour
90
91 * Added $+$
92
93 * Corrected and tidied up the laws and invariants
94
95 ======================================================================
96 Relative to John's original paper, there are the following new features:
97
98 1. There's an empty document, "empty". It's a left and right unit for
99 both <> and $$, and anywhere in the argument list for
100 sep, hcat, hsep, vcat, fcat etc.
101
102 It is Really Useful in practice.
103
104 2. There is a paragraph-fill combinator, fsep, that's much like sep,
105 only it keeps fitting things on one line until it can't fit any more.
106
107 3. Some random useful extra combinators are provided.
108 <+> puts its arguments beside each other with a space between them,
109 unless either argument is empty in which case it returns the other
110
111
112 hcat is a list version of <>
113 hsep is a list version of <+>
114 vcat is a list version of $$
115
116 sep (separate) is either like hsep or like vcat, depending on what fits
117
118 cat behaves like sep, but it uses <> for horizontal conposition
119 fcat behaves like fsep, but it uses <> for horizontal conposition
120
121 These new ones do the obvious things:
122 char, semi, comma, colon, space,
123 parens, brackets, braces,
124 quotes, doubleQuotes
125
126 4. The "above" combinator, $$, now overlaps its two arguments if the
127 last line of the top argument stops before the first line of the
128 second begins.
129
130 For example: text "hi" $$ nest 5 "there"
131 lays out as
132 hi there
133 rather than
134 hi
135 there
136
137 There are two places this is really useful
138
139 a) When making labelled blocks, like this:
140 Left -> code for left
141 Right -> code for right
142 LongLongLongLabel ->
143 code for longlonglonglabel
144 The block is on the same line as the label if the label is
145 short, but on the next line otherwise.
146
147 b) When laying out lists like this:
148 [ first
149 , second
150 , third
151 ]
152 which some people like. But if the list fits on one line
153 you want [first, second, third]. You can't do this with
154 John's original combinators, but it's quite easy with the
155 new $$.
156
157 The combinator $+$ gives the original "never-overlap" behaviour.
158
159 5. Several different renderers are provided:
160 * a standard one
161 * one that uses cut-marks to avoid deeply-nested documents
162 simply piling up in the right-hand margin
163 * one that ignores indentation (fewer chars output; good for machines)
164 * one that ignores indentation and newlines (ditto, only more so)
165
166 6. Numerous implementation tidy-ups
167 Use of unboxed data types to speed up the implementation
168 -}
169
170 module Text.PrettyPrint.HughesPJ (
171
172 -- * The document type
173 Doc, -- Abstract
174
175 -- * Primitive Documents
176 empty,
177 semi, comma, colon, space, equals,
178 lparen, rparen, lbrack, rbrack, lbrace, rbrace,
179
180 -- * Converting values into documents
181 text, char, ptext,
182 int, integer, float, double, rational,
183
184 -- * Wrapping documents in delimiters
185 parens, brackets, braces, quotes, doubleQuotes,
186
187 -- * Combining documents
188 (<>), (<+>), hcat, hsep,
189 ($$), ($+$), vcat,
190 sep, cat,
191 fsep, fcat,
192 nest,
193 hang, punctuate,
194
195 -- * Predicates on documents
196 isEmpty,
197
198 -- * Rendering documents
199
200 -- ** Default rendering
201 render,
202
203 -- ** Rendering with a particular style
204 Style(..),
205 style,
206 renderStyle,
207
208 -- ** General rendering
209 fullRender,
210 Mode(..), TextDetails(..),
211
212 ) where
213
214
215 import Prelude
216
217 infixl 6 <>
218 infixl 6 <+>
219 infixl 5 $$, $+$
220
221 -- ---------------------------------------------------------------------------
222 -- The interface
223
224 -- The primitive Doc values
225
226 isEmpty :: Doc -> Bool; -- ^ Returns 'True' if the document is empty
227
228 empty :: Doc; -- ^ An empty document
229 semi :: Doc; -- ^ A ';' character
230 comma :: Doc; -- ^ A ',' character
231 colon :: Doc; -- ^ A ':' character
232 space :: Doc; -- ^ A space character
233 equals :: Doc; -- ^ A '=' character
234 lparen :: Doc; -- ^ A '(' character
235 rparen :: Doc; -- ^ A ')' character
236 lbrack :: Doc; -- ^ A '[' character
237 rbrack :: Doc; -- ^ A ']' character
238 lbrace :: Doc; -- ^ A '{' character
239 rbrace :: Doc; -- ^ A '}' character
240
241 text :: String -> Doc
242 ptext :: String -> Doc
243 char :: Char -> Doc
244 int :: Int -> Doc
245 integer :: Integer -> Doc
246 float :: Float -> Doc
247 double :: Double -> Doc
248 rational :: Rational -> Doc
249
250
251 parens :: Doc -> Doc; -- ^ Wrap document in @(...)@
252 brackets :: Doc -> Doc; -- ^ Wrap document in @[...]@
253 braces :: Doc -> Doc; -- ^ Wrap document in @{...}@
254 quotes :: Doc -> Doc; -- ^ Wrap document in @'...'@
255 doubleQuotes :: Doc -> Doc; -- ^ Wrap document in @\"...\"@
256
257 -- Combining @Doc@ values
258
259 (<>) :: Doc -> Doc -> Doc; -- ^Beside
260 hcat :: [Doc] -> Doc; -- ^List version of '<>'
261 (<+>) :: Doc -> Doc -> Doc; -- ^Beside, separated by space
262 hsep :: [Doc] -> Doc; -- ^List version of '<+>'
263
264 ($$) :: Doc -> Doc -> Doc; -- ^Above; if there is no
265 -- overlap it \"dovetails\" the two
266 vcat :: [Doc] -> Doc; -- ^List version of '$$'
267
268 cat :: [Doc] -> Doc; -- ^ Either hcat or vcat
269 sep :: [Doc] -> Doc; -- ^ Either hsep or vcat
270 fcat :: [Doc] -> Doc; -- ^ \"Paragraph fill\" version of cat
271 fsep :: [Doc] -> Doc; -- ^ \"Paragraph fill\" version of sep
272
273 nest :: Int -> Doc -> Doc; -- ^ Nested
274
275
276 -- GHC-specific ones.
277
278 hang :: Doc -> Int -> Doc -> Doc; -- ^ @hang d1 n d2 = sep [d1, nest n d2]@
279 punctuate :: Doc -> [Doc] -> [Doc]; -- ^ @punctuate p [d1, ... dn] = [d1 \<> p, d2 \<> p, ... dn-1 \<> p, dn]@
280
281
282 -- Displaying @Doc@ values.
283
284 instance Show Doc where
285 showsPrec prec doc cont = showDoc doc cont
286
287 -- | Renders the document as a string using the default style
288 render :: Doc -> String
289
290 -- | The general rendering interface
291 fullRender :: Mode -- ^Rendering mode
292 -> Int -- ^Line length
293 -> Float -- ^Ribbons per line
294 -> (TextDetails -> a -> a) -- ^What to do with text
295 -> a -- ^What to do at the end
296 -> Doc -- ^The document
297 -> a -- ^Result
298
299 -- | Render the document as a string using a specified style
300 renderStyle :: Style -> Doc -> String
301
302 -- | A rendering style
303 data Style
304 = Style { mode :: Mode -- ^ The rendering mode
305 , lineLength :: Int -- ^ Length of line, in chars
306 , ribbonsPerLine :: Float -- ^ Ratio of ribbon length to line length
307 }
308
309 -- | The default style (@mode=PageMode, lineLength=100, ribbonsPerLine=1.5@)
310 style :: Style
311 style = Style { lineLength = 100, ribbonsPerLine = 1.5, mode = PageMode }
312
313 -- | Rendering mode
314 data Mode = PageMode -- ^Normal
315 | ZigZagMode -- ^With zig-zag cuts
316 | LeftMode -- ^No indentation, infinitely long lines
317 | OneLineMode -- ^All on one line
318
319 -- ---------------------------------------------------------------------------
320 -- The Doc calculus
321
322 -- The Doc combinators satisfy the following laws:
323
324 {-
325 Laws for $$
326 ~~~~~~~~~~~
327 <a1> (x $$ y) $$ z = x $$ (y $$ z)
328 <a2> empty $$ x = x
329 <a3> x $$ empty = x
330
331 ...ditto $+$...
332
333 Laws for <>
334 ~~~~~~~~~~~
335 <b1> (x <> y) <> z = x <> (y <> z)
336 <b2> empty <> x = empty
337 <b3> x <> empty = x
338
339 ...ditto <+>...
340
341 Laws for text
342 ~~~~~~~~~~~~~
343 <t1> text s <> text t = text (s++t)
344 <t2> text "" <> x = x, if x non-empty
345
346 Laws for nest
347 ~~~~~~~~~~~~~
348 <n1> nest 0 x = x
349 <n2> nest k (nest k' x) = nest (k+k') x
350 <n3> nest k (x <> y) = nest k z <> nest k y
351 <n4> nest k (x $$ y) = nest k x $$ nest k y
352 <n5> nest k empty = empty
353 <n6> x <> nest k y = x <> y, if x non-empty
354
355 ** Note the side condition on <n6>! It is this that
356 ** makes it OK for empty to be a left unit for <>.
357
358 Miscellaneous
359 ~~~~~~~~~~~~~
360 <m1> (text s <> x) $$ y = text s <> ((text "" <> x)) $$
361 nest (-length s) y)
362
363 <m2> (x $$ y) <> z = x $$ (y <> z)
364 if y non-empty
365
366
367 Laws for list versions
368 ~~~~~~~~~~~~~~~~~~~~~~
369 <l1> sep (ps++[empty]++qs) = sep (ps ++ qs)
370 ...ditto hsep, hcat, vcat, fill...
371
372 <l2> nest k (sep ps) = sep (map (nest k) ps)
373 ...ditto hsep, hcat, vcat, fill...
374
375 Laws for oneLiner
376 ~~~~~~~~~~~~~~~~~
377 <o1> oneLiner (nest k p) = nest k (oneLiner p)
378 <o2> oneLiner (x <> y) = oneLiner x <> oneLiner y
379
380 You might think that the following verion of <m1> would
381 be neater:
382
383 <3 NO> (text s <> x) $$ y = text s <> ((empty <> x)) $$
384 nest (-length s) y)
385
386 But it doesn't work, for if x=empty, we would have
387
388 text s $$ y = text s <> (empty $$ nest (-length s) y)
389 = text s <> nest (-length s) y
390 -}
391
392 -- ---------------------------------------------------------------------------
393 -- Simple derived definitions
394
395 semi = char ';'
396 colon = char ':'
397 comma = char ','
398 space = char ' '
399 equals = char '='
400 lparen = char '('
401 rparen = char ')'
402 lbrack = char '['
403 rbrack = char ']'
404 lbrace = char '{'
405 rbrace = char '}'
406
407 int n = text (show n)
408 integer n = text (show n)
409 float n = text (show n)
410 double n = text (show n)
411 rational n = text (show n)
412 -- SIGBJORN wrote instead:
413 -- rational n = text (show (fromRationalX n))
414
415 quotes p = char '`' <> p <> char '\''
416 doubleQuotes p = char '"' <> p <> char '"'
417 parens p = char '(' <> p <> char ')'
418 brackets p = char '[' <> p <> char ']'
419 braces p = char '{' <> p <> char '}'
420
421
422 hcat = foldr (<>) empty
423 hsep = foldr (<+>) empty
424 vcat = foldr ($$) empty
425
426 hang d1 n d2 = sep [d1, nest n d2]
427
428 punctuate p [] = []
429 punctuate p (d:ds) = go d ds
430 where
431 go d [] = [d]
432 go d (e:es) = (d <> p) : go e es
433
434 -- ---------------------------------------------------------------------------
435 -- The Doc data type
436
437 -- A Doc represents a *set* of layouts. A Doc with
438 -- no occurrences of Union or NoDoc represents just one layout.
439
440 -- | The abstract type of documents
441 data Doc
442 = Empty -- empty
443 | NilAbove Doc -- text "" $$ x
444 | TextBeside TextDetails !Int Doc -- text s <> x
445 | Nest !Int Doc -- nest k x
446 | Union Doc Doc -- ul `union` ur
447 | NoDoc -- The empty set of documents
448 | Beside Doc Bool Doc -- True <=> space between
449 | Above Doc Bool Doc -- True <=> never overlap
450
451 type RDoc = Doc -- RDoc is a "reduced Doc", guaranteed not to have a top-level Above or Beside
452
453
454 reduceDoc :: Doc -> RDoc
455 reduceDoc (Beside p g q) = beside p g (reduceDoc q)
456 reduceDoc (Above p g q) = above p g (reduceDoc q)
457 reduceDoc p = p
458
459
460 data TextDetails = Chr Char
461 | Str String
462 | PStr String
463 space_text = Chr ' '
464 nl_text = Chr '\n'
465
466 {-
467 Here are the invariants:
468
469 * The argument of NilAbove is never Empty. Therefore
470 a NilAbove occupies at least two lines.
471
472 * The arugment of @TextBeside@ is never @Nest@.
473
474
475 * The layouts of the two arguments of @Union@ both flatten to the same
476 string.
477
478 * The arguments of @Union@ are either @TextBeside@, or @NilAbove@.
479
480 * The right argument of a union cannot be equivalent to the empty set
481 (@NoDoc@). If the left argument of a union is equivalent to the
482 empty set (@NoDoc@), then the @NoDoc@ appears in the first line.
483
484 * An empty document is always represented by @Empty@. It can't be
485 hidden inside a @Nest@, or a @Union@ of two @Empty@s.
486
487 * The first line of every layout in the left argument of @Union@ is
488 longer than the first line of any layout in the right argument.
489 (1) ensures that the left argument has a first line. In view of
490 (3), this invariant means that the right argument must have at
491 least two lines.
492 -}
493
494 -- Arg of a NilAbove is always an RDoc
495 nilAbove_ p = NilAbove p
496
497 -- Arg of a TextBeside is always an RDoc
498 textBeside_ s sl p = TextBeside s sl p
499
500 -- Arg of Nest is always an RDoc
501 nest_ k p = Nest k p
502
503 -- Args of union are always RDocs
504 union_ p q = Union p q
505
506
507 -- Notice the difference between
508 -- * NoDoc (no documents)
509 -- * Empty (one empty document; no height and no width)
510 -- * text "" (a document containing the empty string;
511 -- one line high, but has no width)
512
513
514 -- ---------------------------------------------------------------------------
515 -- @empty@, @text@, @nest@, @union@
516
517 empty = Empty
518
519 isEmpty Empty = True
520 isEmpty _ = False
521
522 char c = textBeside_ (Chr c) 1 Empty
523 text s = case length s of {sl -> textBeside_ (Str s) sl Empty}
524 ptext s = case length s of {sl -> textBeside_ (PStr s) sl Empty}
525
526 nest k p = mkNest k (reduceDoc p) -- Externally callable version
527
528 -- mkNest checks for Nest's invariant that it doesn't have an Empty inside it
529 mkNest k _ | k `seq` False = undefined
530 mkNest k (Nest k1 p) = mkNest (k + k1) p
531 mkNest k NoDoc = NoDoc
532 mkNest k Empty = Empty
533 mkNest 0 p = p -- Worth a try!
534 mkNest k p = nest_ k p
535
536 -- mkUnion checks for an empty document
537 mkUnion Empty q = Empty
538 mkUnion p q = p `union_` q
539
540 -- ---------------------------------------------------------------------------
541 -- Vertical composition @$$@
542
543 p $$ q = Above p False q
544 p $+$ q = Above p True q
545
546 above :: Doc -> Bool -> RDoc -> RDoc
547 above (Above p g1 q1) g2 q2 = above p g1 (above q1 g2 q2)
548 above p@(Beside _ _ _) g q = aboveNest (reduceDoc p) g 0 (reduceDoc q)
549 above p g q = aboveNest p g 0 (reduceDoc q)
550
551 aboveNest :: RDoc -> Bool -> Int -> RDoc -> RDoc
552 -- Specfication: aboveNest p g k q = p $g$ (nest k q)
553
554 aboveNest _ _ k _ | k `seq` False = undefined
555 aboveNest NoDoc g k q = NoDoc
556 aboveNest (p1 `Union` p2) g k q = aboveNest p1 g k q `union_`
557 aboveNest p2 g k q
558
559 aboveNest Empty g k q = mkNest k q
560 aboveNest (Nest k1 p) g k q = nest_ k1 (aboveNest p g (k - k1) q)
561 -- p can't be Empty, so no need for mkNest
562
563 aboveNest (NilAbove p) g k q = nilAbove_ (aboveNest p g k q)
564 aboveNest (TextBeside s sl p) g k q = k1 `seq` textBeside_ s sl rest
565 where
566 k1 = k - sl
567 rest = case p of
568 Empty -> nilAboveNest g k1 q
569 other -> aboveNest p g k1 q
570
571
572 nilAboveNest :: Bool -> Int -> RDoc -> RDoc
573 -- Specification: text s <> nilaboveNest g k q
574 -- = text s <> (text "" $g$ nest k q)
575
576 nilAboveNest _ k _ | k `seq` False = undefined
577 nilAboveNest g k Empty = Empty -- Here's why the "text s <>" is in the spec!
578 nilAboveNest g k (Nest k1 q) = nilAboveNest g (k + k1) q
579
580 nilAboveNest g k q | (not g) && (k > 0) -- No newline if no overlap
581 = textBeside_ (Str (spaces k)) k q
582 | otherwise -- Put them really above
583 = nilAbove_ (mkNest k q)
584
585 -- ---------------------------------------------------------------------------
586 -- Horizontal composition @<>@
587
588 p <> q = Beside p False q
589 p <+> q = Beside p True q
590
591 beside :: Doc -> Bool -> RDoc -> RDoc
592 -- Specification: beside g p q = p <g> q
593
594 beside NoDoc g q = NoDoc
595 beside (p1 `Union` p2) g q = (beside p1 g q) `union_` (beside p2 g q)
596 beside Empty g q = q
597 beside (Nest k p) g q = nest_ k (beside p g q) -- p non-empty
598 beside p@(Beside p1 g1 q1) g2 q2
599 {- (A `op1` B) `op2` C == A `op1` (B `op2` C) iff op1 == op2
600 [ && (op1 == <> || op1 == <+>) ] -}
601 | g1 == g2 = beside p1 g1 (beside q1 g2 q2)
602 | otherwise = beside (reduceDoc p) g2 q2
603 beside p@(Above _ _ _) g q = beside (reduceDoc p) g q
604 beside (NilAbove p) g q = nilAbove_ (beside p g q)
605 beside (TextBeside s sl p) g q = textBeside_ s sl rest
606 where
607 rest = case p of
608 Empty -> nilBeside g q
609 other -> beside p g q
610
611
612 nilBeside :: Bool -> RDoc -> RDoc
613 -- Specification: text "" <> nilBeside g p
614 -- = text "" <g> p
615
616 nilBeside g Empty = Empty -- Hence the text "" in the spec
617 nilBeside g (Nest _ p) = nilBeside g p
618 nilBeside g p | g = textBeside_ space_text 1 p
619 | otherwise = p
620
621 -- ---------------------------------------------------------------------------
622 -- Separate, @sep@, Hughes version
623
624 -- Specification: sep ps = oneLiner (hsep ps)
625 -- `union`
626 -- vcat ps
627
628 sep = sepX True -- Separate with spaces
629 cat = sepX False -- Don't
630
631 sepX x [] = empty
632 sepX x (p:ps) = sep1 x (reduceDoc p) 0 ps
633
634
635 -- Specification: sep1 g k ys = sep (x : map (nest k) ys)
636 -- = oneLiner (x <g> nest k (hsep ys))
637 -- `union` x $$ nest k (vcat ys)
638
639 sep1 :: Bool -> RDoc -> Int -> [Doc] -> RDoc
640 sep1 g _ k ys | k `seq` False = undefined
641 sep1 g NoDoc k ys = NoDoc
642 sep1 g (p `Union` q) k ys = sep1 g p k ys
643 `union_`
644 (aboveNest q False k (reduceDoc (vcat ys)))
645
646 sep1 g Empty k ys = mkNest k (sepX g ys)
647 sep1 g (Nest n p) k ys = nest_ n (sep1 g p (k - n) ys)
648
649 sep1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (reduceDoc (vcat ys)))
650 sep1 g (TextBeside s sl p) k ys = textBeside_ s sl (sepNB g p (k - sl) ys)
651
652 -- Specification: sepNB p k ys = sep1 (text "" <> p) k ys
653 -- Called when we have already found some text in the first item
654 -- We have to eat up nests
655
656 sepNB g (Nest _ p) k ys = sepNB g p k ys
657
658 sepNB g Empty k ys = oneLiner (nilBeside g (reduceDoc rest))
659 `mkUnion`
660 nilAboveNest False k (reduceDoc (vcat ys))
661 where
662 rest | g = hsep ys
663 | otherwise = hcat ys
664
665 sepNB g p k ys = sep1 g p k ys
666
667 -- ---------------------------------------------------------------------------
668 -- @fill@
669
670 fsep = fill True
671 fcat = fill False
672
673 -- Specification:
674 -- fill [] = empty
675 -- fill [p] = p
676 -- fill (p1:p2:ps) = oneLiner p1 <#> nest (length p1)
677 -- (fill (oneLiner p2 : ps))
678 -- `union`
679 -- p1 $$ fill ps
680
681 fill g [] = empty
682 fill g (p:ps) = fill1 g (reduceDoc p) 0 ps
683
684
685 fill1 :: Bool -> RDoc -> Int -> [Doc] -> Doc
686 fill1 g _ k ys | k `seq` False = undefined
687 fill1 g NoDoc k ys = NoDoc
688 fill1 g (p `Union` q) k ys = fill1 g p k ys
689 `union_`
690 (aboveNest q False k (fill g ys))
691
692 fill1 g Empty k ys = mkNest k (fill g ys)
693 fill1 g (Nest n p) k ys = nest_ n (fill1 g p (k - n) ys)
694
695 fill1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (fill g ys))
696 fill1 g (TextBeside s sl p) k ys = textBeside_ s sl (fillNB g p (k - sl) ys)
697
698 fillNB g _ k ys | k `seq` False = undefined
699 fillNB g (Nest _ p) k ys = fillNB g p k ys
700 fillNB g Empty k [] = Empty
701 fillNB g Empty k (y:ys) = nilBeside g (fill1 g (oneLiner (reduceDoc y)) k1 ys)
702 `mkUnion`
703 nilAboveNest False k (fill g (y:ys))
704 where
705 k1 | g = k - 1
706 | otherwise = k
707
708 fillNB g p k ys = fill1 g p k ys
709
710
711 -- ---------------------------------------------------------------------------
712 -- Selecting the best layout
713
714 best :: Mode
715 -> Int -- Line length
716 -> Int -- Ribbon length
717 -> RDoc
718 -> RDoc -- No unions in here!
719
720 best OneLineMode w r p
721 = get p
722 where
723 get Empty = Empty
724 get NoDoc = NoDoc
725 get (NilAbove p) = nilAbove_ (get p)
726 get (TextBeside s sl p) = textBeside_ s sl (get p)
727 get (Nest k p) = get p -- Elide nest
728 get (p `Union` q) = first (get p) (get q)
729
730 best mode w r p
731 = get w p
732 where
733 get :: Int -- (Remaining) width of line
734 -> Doc -> Doc
735 get w _ | w==0 && False = undefined
736 get w Empty = Empty
737 get w NoDoc = NoDoc
738 get w (NilAbove p) = nilAbove_ (get w p)
739 get w (TextBeside s sl p) = textBeside_ s sl (get1 w sl p)
740 get w (Nest k p) = nest_ k (get (w - k) p)
741 get w (p `Union` q) = nicest w r (get w p) (get w q)
742
743 get1 :: Int -- (Remaining) width of line
744 -> Int -- Amount of first line already eaten up
745 -> Doc -- This is an argument to TextBeside => eat Nests
746 -> Doc -- No unions in here!
747
748 get1 w _ _ | w==0 && False = undefined
749 get1 w sl Empty = Empty
750 get1 w sl NoDoc = NoDoc
751 get1 w sl (NilAbove p) = nilAbove_ (get (w - sl) p)
752 get1 w sl (TextBeside t tl p) = textBeside_ t tl (get1 w (sl + tl) p)
753 get1 w sl (Nest k p) = get1 w sl p
754 get1 w sl (p `Union` q) = nicest1 w r sl (get1 w sl p)
755 (get1 w sl q)
756
757 nicest w r p q = nicest1 w r 0 p q
758 nicest1 w r sl p q | fits ((w `minn` r) - sl) p = p
759 | otherwise = q
760
761 fits :: Int -- Space available
762 -> Doc
763 -> Bool -- True if *first line* of Doc fits in space available
764
765 fits n p | n < 0 = False
766 fits n NoDoc = False
767 fits n Empty = True
768 fits n (NilAbove _) = True
769 fits n (TextBeside _ sl p) = fits (n - sl) p
770
771 minn x y | x < y = x
772 | otherwise = y
773
774 -- @first@ and @nonEmptySet@ are similar to @nicest@ and @fits@, only simpler.
775 -- @first@ returns its first argument if it is non-empty, otherwise its second.
776
777 first p q | nonEmptySet p = p
778 | otherwise = q
779
780 nonEmptySet NoDoc = False
781 nonEmptySet (p `Union` q) = True
782 nonEmptySet Empty = True
783 nonEmptySet (NilAbove p) = True -- NoDoc always in first line
784 nonEmptySet (TextBeside _ _ p) = nonEmptySet p
785 nonEmptySet (Nest _ p) = nonEmptySet p
786
787 -- @oneLiner@ returns the one-line members of the given set of @Doc@s.
788
789 oneLiner :: Doc -> Doc
790 oneLiner NoDoc = NoDoc
791 oneLiner Empty = Empty
792 oneLiner (NilAbove p) = NoDoc
793 oneLiner (TextBeside s sl p) = textBeside_ s sl (oneLiner p)
794 oneLiner (Nest k p) = nest_ k (oneLiner p)
795 oneLiner (p `Union` q) = oneLiner p
796
797
798 -- ---------------------------------------------------------------------------
799 -- Displaying the best layout
800
801 renderStyle style doc
802 = fullRender (mode style)
803 (lineLength style)
804 (ribbonsPerLine style)
805 string_txt
806 ""
807 doc
808
809 render doc = showDoc doc ""
810 showDoc doc rest = fullRender PageMode 100 1.5 string_txt rest doc
811
812 string_txt (Chr c) s = c:s
813 string_txt (Str s1) s2 = s1 ++ s2
814 string_txt (PStr s1) s2 = s1 ++ s2
815
816
817 fullRender OneLineMode _ _ txt end doc = easy_display space_text txt end (reduceDoc doc)
818 fullRender LeftMode _ _ txt end doc = easy_display nl_text txt end (reduceDoc doc)
819
820 fullRender mode line_length ribbons_per_line txt end doc
821 = display mode line_length ribbon_length txt end best_doc
822 where
823 best_doc = best mode hacked_line_length ribbon_length (reduceDoc doc)
824
825 hacked_line_length, ribbon_length :: Int
826 ribbon_length = round (fromIntegral line_length / ribbons_per_line)
827 hacked_line_length = case mode of { ZigZagMode -> maxBound; other -> line_length }
828
829 display mode page_width ribbon_width txt end doc
830 = case page_width - ribbon_width of { gap_width ->
831 case gap_width `quot` 2 of { shift ->
832 let
833 lay k _ | k `seq` False = undefined
834 lay k (Nest k1 p) = lay (k + k1) p
835 lay k Empty = end
836
837 lay k (NilAbove p) = nl_text `txt` lay k p
838
839 lay k (TextBeside s sl p)
840 = case mode of
841 ZigZagMode | k >= gap_width
842 -> nl_text `txt` (
843 Str (multi_ch shift '/') `txt` (
844 nl_text `txt` (
845 lay1 (k - shift) s sl p)))
846
847 | k < 0
848 -> nl_text `txt` (
849 Str (multi_ch shift '\\') `txt` (
850 nl_text `txt` (
851 lay1 (k + shift) s sl p )))
852
853 other -> lay1 k s sl p
854
855 lay1 k _ sl _ | k+sl `seq` False = undefined
856 lay1 k s sl p = Str (indent k) `txt` (s `txt` lay2 (k + sl) p)
857
858 lay2 k _ | k `seq` False = undefined
859 lay2 k (NilAbove p) = nl_text `txt` lay k p
860 lay2 k (TextBeside s sl p) = s `txt` (lay2 (k + sl) p)
861 lay2 k (Nest _ p) = lay2 k p
862 lay2 k Empty = end
863 in
864 lay 0 doc
865 }}
866
867 cant_fail = error "easy_display: NoDoc"
868 easy_display nl_text txt end doc
869 = lay doc cant_fail
870 where
871 lay NoDoc no_doc = no_doc
872 lay (Union p q) no_doc = {- lay p -} (lay q cant_fail) -- Second arg can't be NoDoc
873 lay (Nest k p) no_doc = lay p no_doc
874 lay Empty no_doc = end
875 lay (NilAbove p) no_doc = nl_text `txt` lay p cant_fail -- NoDoc always on first line
876 lay (TextBeside s sl p) no_doc = s `txt` lay p no_doc
877
878 indent n | n >= 8 = '\t' : indent (n - 8)
879 | otherwise = spaces n
880
881 multi_ch 0 ch = ""
882 multi_ch n ch = ch : multi_ch (n - 1) ch
883
884 spaces 0 = ""
885 spaces n = ' ' : spaces (n - 1)
886