-----------------------------------------------------------------------------
-- |
-- Module : Text.PrettyPrint.HughesPJ
-- Copyright : (c) The University of Glasgow 2001
-- License : BSD-style (see the file libraries/base/LICENSE)
--
-- Maintainer : libraries@haskell.org
-- Stability : provisional
-- Portability : portable
--
-- John Hughes's and Simon Peyton Jones's Pretty Printer Combinators
--
-- Based on /The Design of a Pretty-printing Library/
-- in Advanced Functional Programming,
-- Johan Jeuring and Erik Meijer (eds), LNCS 925
-- <http://www.cs.chalmers.se/~rjmh/Papers/pretty.ps>
--
-- Heavily modified by Simon Peyton Jones, Dec 96
--
-----------------------------------------------------------------------------
{-
Version 3.0 28 May 1997
* Cured massive performance bug. If you write
foldl <> empty (map (text.show) [1..10000])
you get quadratic behaviour with V2.0. Why? For just the same
reason as you get quadratic behaviour with left-associated (++)
chains.
This is really bad news. One thing a pretty-printer abstraction
should certainly guarantee is insensivity to associativity. It
matters: suddenly GHC's compilation times went up by a factor of
100 when I switched to the new pretty printer.
I fixed it with a bit of a hack (because I wanted to get GHC back
on the road). I added two new constructors to the Doc type, Above
and Beside:
<> = Beside
$$ = Above
Then, where I need to get to a "TextBeside" or "NilAbove" form I
"force" the Doc to squeeze out these suspended calls to Beside and
Above; but in so doing I re-associate. It's quite simple, but I'm
not satisfied that I've done the best possible job. I'll send you
the code if you are interested.
* Added new exports:
punctuate, hang
int, integer, float, double, rational,
lparen, rparen, lbrack, rbrack, lbrace, rbrace,
* fullRender's type signature has changed. Rather than producing a
string it now takes an extra couple of arguments that tells it how
to glue fragments of output together:
fullRender :: Mode
-> Int -- Line length
-> Float -- Ribbons per line
-> (TextDetails -> a -> a) -- What to do with text
-> a -- What to do at the end
-> Doc
-> a -- Result
The "fragments" are encapsulated in the TextDetails data type:
data TextDetails = Chr Char
| Str String
| PStr FAST_STRING
The Chr and Str constructors are obvious enough. The PStr
constructor has a packed string (FAST_STRING) inside it. It's
generated by using the new "ptext" export.
An advantage of this new setup is that you can get the renderer to
do output directly (by passing in a function of type (TextDetails
-> IO () -> IO ()), rather than producing a string that you then
print.
Version 2.0 24 April 1997
* Made empty into a left unit for <> as well as a right unit;
it is also now true that
nest k empty = empty
which wasn't true before.
* Fixed an obscure bug in sep that occassionally gave very weird behaviour
* Added $+$
* Corrected and tidied up the laws and invariants
======================================================================
Relative to John's original paper, there are the following new features:
1. There's an empty document, "empty". It's a left and right unit for
both <> and $$, and anywhere in the argument list for
sep, hcat, hsep, vcat, fcat etc.
It is Really Useful in practice.
2. There is a paragraph-fill combinator, fsep, that's much like sep,
only it keeps fitting things on one line until it can't fit any more.
3. Some random useful extra combinators are provided.
<+> puts its arguments beside each other with a space between them,
unless either argument is empty in which case it returns the other
hcat is a list version of <>
hsep is a list version of <+>
vcat is a list version of $$
sep (separate) is either like hsep or like vcat, depending on what fits
cat behaves like sep, but it uses <> for horizontal conposition
fcat behaves like fsep, but it uses <> for horizontal conposition
These new ones do the obvious things:
char, semi, comma, colon, space,
parens, brackets, braces,
quotes, doubleQuotes
4. The "above" combinator, $$, now overlaps its two arguments if the
last line of the top argument stops before the first line of the
second begins.
For example: text "hi" $$ nest 5 (text "there")
lays out as
hi there
rather than
hi
there
There are two places this is really useful
a) When making labelled blocks, like this:
Left -> code for left
Right -> code for right
LongLongLongLabel ->
code for longlonglonglabel
The block is on the same line as the label if the label is
short, but on the next line otherwise.
b) When laying out lists like this:
[ first
, second
, third
]
which some people like. But if the list fits on one line
you want [first, second, third]. You can't do this with
John's original combinators, but it's quite easy with the
new $$.
The combinator $+$ gives the original "never-overlap" behaviour.
5. Several different renderers are provided:
* a standard one
* one that uses cut-marks to avoid deeply-nested documents
simply piling up in the right-hand margin
* one that ignores indentation (fewer chars output; good for machines)
* one that ignores indentation and newlines (ditto, only more so)
6. Numerous implementation tidy-ups
Use of unboxed data types to speed up the implementation
-}
module Text.PrettyPrint.HughesPJ (
-- * The document type
Doc, -- Abstract
-- * Constructing documents
-- ** Converting values into documents
char, text, ptext,
int, integer, float, double, rational,
-- ** Simple derived documents
semi, comma, colon, space, equals,
lparen, rparen, lbrack, rbrack, lbrace, rbrace,
-- ** Wrapping documents in delimiters
parens, brackets, braces, quotes, doubleQuotes,
-- ** Combining documents
empty,
(<>), (<+>), hcat, hsep,
($$), ($+$), vcat,
sep, cat,
fsep, fcat,
nest,
hang, punctuate,
-- * Predicates on documents
isEmpty,
-- * Rendering documents
-- ** Default rendering
render,
-- ** Rendering with a particular style
Style(..),
style,
renderStyle,
-- ** General rendering
fullRender,
Mode(..), TextDetails(..),
) where
import Prelude
infixl 6 <>
infixl 6 <+>
infixl 5 $$, $+$
-- ---------------------------------------------------------------------------
-- The interface
-- The primitive Doc values
isEmpty :: Doc -> Bool; -- ^ Returns 'True' if the document is empty
-- | The empty document, with no height and no width.
-- 'empty' is the identity for '<>', '<+>', '$$' and '$+$', and anywhere
-- in the argument list for 'sep', 'hcat', 'hsep', 'vcat', 'fcat' etc.
empty :: Doc
semi :: Doc; -- ^ A ';' character
comma :: Doc; -- ^ A ',' character
colon :: Doc; -- ^ A ':' character
space :: Doc; -- ^ A space character
equals :: Doc; -- ^ A '=' character
lparen :: Doc; -- ^ A '(' character
rparen :: Doc; -- ^ A ')' character
lbrack :: Doc; -- ^ A '[' character
rbrack :: Doc; -- ^ A ']' character
lbrace :: Doc; -- ^ A '{' character
rbrace :: Doc; -- ^ A '}' character
-- | A document of height and width 1, containing a literal character.
char :: Char -> Doc
-- | A document of height 1 containing a literal string.
-- 'text' satisfies the following laws:
--
-- * @'text' s '<>' 'text' t = 'text' (s'++'t)@
--
-- * @'text' \"\" '<>' x = x@, if @x@ non-empty
--
-- The side condition on the last law is necessary because @'text' \"\"@
-- has height 1, while 'empty' has no height.
text :: String -> Doc
-- | An obsolete function, now identical to 'text'.
ptext :: String -> Doc
int :: Int -> Doc; -- ^ @int n = text (show n)@
integer :: Integer -> Doc; -- ^ @integer n = text (show n)@
float :: Float -> Doc; -- ^ @float n = text (show n)@
double :: Double -> Doc; -- ^ @double n = text (show n)@
rational :: Rational -> Doc; -- ^ @rational n = text (show n)@
parens :: Doc -> Doc; -- ^ Wrap document in @(...)@
brackets :: Doc -> Doc; -- ^ Wrap document in @[...]@
braces :: Doc -> Doc; -- ^ Wrap document in @{...}@
quotes :: Doc -> Doc; -- ^ Wrap document in @\'...\'@
doubleQuotes :: Doc -> Doc; -- ^ Wrap document in @\"...\"@
-- Combining @Doc@ values
-- | Beside.
-- '<>' is associative, with identity 'empty'.
(<>) :: Doc -> Doc -> Doc
-- | Beside, separated by space, unless one of the arguments is 'empty'.
-- '<+>' is associative, with identity 'empty'.
(<+>) :: Doc -> Doc -> Doc
-- | Above, except that if the last line of the first argument stops
-- at least one position before the first line of the second begins,
-- these two lines are overlapped. For example:
--
-- > text "hi" $$ nest 5 (text "there")
--
-- lays out as
--
-- > hi there
--
-- rather than
--
-- > hi
-- > there
--
-- '$$' is associative, with identity 'empty', and also satisfies
--
-- * @(x '$$' y) '<>' z = x '$$' (y '<>' z)@, if @y@ non-empty.
--
($$) :: Doc -> Doc -> Doc
-- | Above, with no overlapping.
-- '$+$' is associative, with identity 'empty'.
($+$) :: Doc -> Doc -> Doc
hcat :: [Doc] -> Doc; -- ^List version of '<>'.
hsep :: [Doc] -> Doc; -- ^List version of '<+>'.
vcat :: [Doc] -> Doc; -- ^List version of '$$'.
cat :: [Doc] -> Doc; -- ^ Either 'hcat' or 'vcat'.
sep :: [Doc] -> Doc; -- ^ Either 'hsep' or 'vcat'.
fcat :: [Doc] -> Doc; -- ^ \"Paragraph fill\" version of 'cat'.
fsep :: [Doc] -> Doc; -- ^ \"Paragraph fill\" version of 'sep'.
-- | Nest (or indent) a document by a given number of positions
-- (which may also be negative). 'nest' satisfies the laws:
--
-- * @'nest' 0 x = x@
--
-- * @'nest' k ('nest' k' x) = 'nest' (k+k') x@
--
-- * @'nest' k (x '<>' y) = 'nest' k z '<>' 'nest' k y@
--
-- * @'nest' k (x '$$' y) = 'nest' k x '$$' 'nest' k y@
--
-- * @'nest' k 'empty' = 'empty'@
--
-- * @x '<>' 'nest' k y = x '<>' y@, if @x@ non-empty
--
-- The side condition on the last law is needed because
-- 'empty' is a left identity for '<>'.
nest :: Int -> Doc -> Doc
-- GHC-specific ones.
-- | @hang d1 n d2 = sep [d1, nest n d2]@
hang :: Doc -> Int -> Doc -> Doc
-- | @punctuate p [d1, ... dn] = [d1 \<> p, d2 \<> p, ... dn-1 \<> p, dn]@
punctuate :: Doc -> [Doc] -> [Doc]
-- Displaying @Doc@ values.
instance Show Doc where
showsPrec prec doc cont = showDoc doc cont
-- | Renders the document as a string using the default 'style'.
render :: Doc -> String
-- | The general rendering interface.
fullRender :: Mode -- ^Rendering mode
-> Int -- ^Line length
-> Float -- ^Ribbons per line
-> (TextDetails -> a -> a) -- ^What to do with text
-> a -- ^What to do at the end
-> Doc -- ^The document
-> a -- ^Result
-- | Render the document as a string using a specified style.
renderStyle :: Style -> Doc -> String
-- | A rendering style.
data Style
= Style { mode :: Mode -- ^ The rendering mode
, lineLength :: Int -- ^ Length of line, in chars
, ribbonsPerLine :: Float -- ^ Ratio of ribbon length to line length
}
-- | The default style (@mode=PageMode, lineLength=100, ribbonsPerLine=1.5@).
style :: Style
style = Style { lineLength = 100, ribbonsPerLine = 1.5, mode = PageMode }
-- | Rendering mode.
data Mode = PageMode -- ^Normal
| ZigZagMode -- ^With zig-zag cuts
| LeftMode -- ^No indentation, infinitely long lines
| OneLineMode -- ^All on one line
-- ---------------------------------------------------------------------------
-- The Doc calculus
-- The Doc combinators satisfy the following laws:
{-
Laws for $$
~~~~~~~~~~~
<a1> (x $$ y) $$ z = x $$ (y $$ z)
<a2> empty $$ x = x
<a3> x $$ empty = x
...ditto $+$...
Laws for <>
~~~~~~~~~~~
<b1> (x <> y) <> z = x <> (y <> z)
<b2> empty <> x = empty
<b3> x <> empty = x
...ditto <+>...
Laws for text
~~~~~~~~~~~~~
<t1> text s <> text t = text (s++t)
<t2> text "" <> x = x, if x non-empty
Laws for nest
~~~~~~~~~~~~~
<n1> nest 0 x = x
<n2> nest k (nest k' x) = nest (k+k') x
<n3> nest k (x <> y) = nest k z <> nest k y
<n4> nest k (x $$ y) = nest k x $$ nest k y
<n5> nest k empty = empty
<n6> x <> nest k y = x <> y, if x non-empty
** Note the side condition on <n6>! It is this that
** makes it OK for empty to be a left unit for <>.
Miscellaneous
~~~~~~~~~~~~~
<m1> (text s <> x) $$ y = text s <> ((text "" <> x)) $$
nest (-length s) y)
<m2> (x $$ y) <> z = x $$ (y <> z)
if y non-empty
Laws for list versions
~~~~~~~~~~~~~~~~~~~~~~
<l1> sep (ps++[empty]++qs) = sep (ps ++ qs)
...ditto hsep, hcat, vcat, fill...
<l2> nest k (sep ps) = sep (map (nest k) ps)
...ditto hsep, hcat, vcat, fill...
Laws for oneLiner
~~~~~~~~~~~~~~~~~
<o1> oneLiner (nest k p) = nest k (oneLiner p)
<o2> oneLiner (x <> y) = oneLiner x <> oneLiner y
You might think that the following verion of <m1> would
be neater:
<3 NO> (text s <> x) $$ y = text s <> ((empty <> x)) $$
nest (-length s) y)
But it doesn't work, for if x=empty, we would have
text s $$ y = text s <> (empty $$ nest (-length s) y)
= text s <> nest (-length s) y
-}
-- ---------------------------------------------------------------------------
-- Simple derived definitions
semi = char ';'
colon = char ':'
comma = char ','
space = char ' '
equals = char '='
lparen = char '('
rparen = char ')'
lbrack = char '['
rbrack = char ']'
lbrace = char '{'
rbrace = char '}'
int n = text (show n)
integer n = text (show n)
float n = text (show n)
double n = text (show n)
rational n = text (show n)
-- SIGBJORN wrote instead:
-- rational n = text (show (fromRationalX n))
quotes p = char '\'' <> p <> char '\''
doubleQuotes p = char '"' <> p <> char '"'
parens p = char '(' <> p <> char ')'
brackets p = char '[' <> p <> char ']'
braces p = char '{' <> p <> char '}'
hcat = foldr (<>) empty
hsep = foldr (<+>) empty
vcat = foldr ($$) empty
hang d1 n d2 = sep [d1, nest n d2]
punctuate p [] = []
punctuate p (d:ds) = go d ds
where
go d [] = [d]
go d (e:es) = (d <> p) : go e es
-- ---------------------------------------------------------------------------
-- The Doc data type
-- A Doc represents a *set* of layouts. A Doc with
-- no occurrences of Union or NoDoc represents just one layout.
-- | The abstract type of documents.
-- The 'Show' instance is equivalent to using 'render'.
data Doc
= Empty -- empty
| NilAbove Doc -- text "" $$ x
| TextBeside TextDetails !Int Doc -- text s <> x
| Nest !Int Doc -- nest k x
| Union Doc Doc -- ul `union` ur
| NoDoc -- The empty set of documents
| Beside Doc Bool Doc -- True <=> space between
| Above Doc Bool Doc -- True <=> never overlap
type RDoc = Doc -- RDoc is a "reduced Doc", guaranteed not to have a top-level Above or Beside
reduceDoc :: Doc -> RDoc
reduceDoc (Beside p g q) = beside p g (reduceDoc q)
reduceDoc (Above p g q) = above p g (reduceDoc q)
reduceDoc p = p
data TextDetails = Chr Char
| Str String
| PStr String
space_text = Chr ' '
nl_text = Chr '\n'
{-
Here are the invariants:
* The argument of NilAbove is never Empty. Therefore
a NilAbove occupies at least two lines.
* The arugment of @TextBeside@ is never @Nest@.
* The layouts of the two arguments of @Union@ both flatten to the same
string.
* The arguments of @Union@ are either @TextBeside@, or @NilAbove@.
* The right argument of a union cannot be equivalent to the empty set
(@NoDoc@). If the left argument of a union is equivalent to the
empty set (@NoDoc@), then the @NoDoc@ appears in the first line.
* An empty document is always represented by @Empty@. It can't be
hidden inside a @Nest@, or a @Union@ of two @Empty@s.
* The first line of every layout in the left argument of @Union@ is
longer than the first line of any layout in the right argument.
(1) ensures that the left argument has a first line. In view of
(3), this invariant means that the right argument must have at
least two lines.
-}
-- Arg of a NilAbove is always an RDoc
nilAbove_ p = NilAbove p
-- Arg of a TextBeside is always an RDoc
textBeside_ s sl p = TextBeside s sl p
-- Arg of Nest is always an RDoc
nest_ k p = Nest k p
-- Args of union are always RDocs
union_ p q = Union p q
-- Notice the difference between
-- * NoDoc (no documents)
-- * Empty (one empty document; no height and no width)
-- * text "" (a document containing the empty string;
-- one line high, but has no width)
-- ---------------------------------------------------------------------------
-- @empty@, @text@, @nest@, @union@
empty = Empty
isEmpty Empty = True
isEmpty _ = False
char c = textBeside_ (Chr c) 1 Empty
text s = case length s of {sl -> textBeside_ (Str s) sl Empty}
ptext s = case length s of {sl -> textBeside_ (PStr s) sl Empty}
nest k p = mkNest k (reduceDoc p) -- Externally callable version
-- mkNest checks for Nest's invariant that it doesn't have an Empty inside it
mkNest k _ | k `seq` False = undefined
mkNest k (Nest k1 p) = mkNest (k + k1) p
mkNest k NoDoc = NoDoc
mkNest k Empty = Empty
mkNest 0 p = p -- Worth a try!
mkNest k p = nest_ k p
-- mkUnion checks for an empty document
mkUnion Empty q = Empty
mkUnion p q = p `union_` q
-- ---------------------------------------------------------------------------
-- Vertical composition @$$@
above_ :: Doc -> Bool -> Doc -> Doc
above_ p _ Empty = p
above_ Empty _ q = q
above_ p g q = Above p g q
p $$ q = above_ p False q
p $+$ q = above_ p True q
above :: Doc -> Bool -> RDoc -> RDoc
above (Above p g1 q1) g2 q2 = above p g1 (above q1 g2 q2)
above p@(Beside _ _ _) g q = aboveNest (reduceDoc p) g 0 (reduceDoc q)
above p g q = aboveNest p g 0 (reduceDoc q)
aboveNest :: RDoc -> Bool -> Int -> RDoc -> RDoc
-- Specfication: aboveNest p g k q = p $g$ (nest k q)
aboveNest _ _ k _ | k `seq` False = undefined
aboveNest NoDoc g k q = NoDoc
aboveNest (p1 `Union` p2) g k q = aboveNest p1 g k q `union_`
aboveNest p2 g k q
aboveNest Empty g k q = mkNest k q
aboveNest (Nest k1 p) g k q = nest_ k1 (aboveNest p g (k - k1) q)
-- p can't be Empty, so no need for mkNest
aboveNest (NilAbove p) g k q = nilAbove_ (aboveNest p g k q)
aboveNest (TextBeside s sl p) g k q = k1 `seq` textBeside_ s sl rest
where
k1 = k - sl
rest = case p of
Empty -> nilAboveNest g k1 q
other -> aboveNest p g k1 q
nilAboveNest :: Bool -> Int -> RDoc -> RDoc
-- Specification: text s <> nilaboveNest g k q
-- = text s <> (text "" $g$ nest k q)
nilAboveNest _ k _ | k `seq` False = undefined
nilAboveNest g k Empty = Empty -- Here's why the "text s <>" is in the spec!
nilAboveNest g k (Nest k1 q) = nilAboveNest g (k + k1) q
nilAboveNest g k q | (not g) && (k > 0) -- No newline if no overlap
= textBeside_ (Str (spaces k)) k q
| otherwise -- Put them really above
= nilAbove_ (mkNest k q)
-- ---------------------------------------------------------------------------
-- Horizontal composition @<>@
beside_ :: Doc -> Bool -> Doc -> Doc
beside_ p _ Empty = p
beside_ Empty _ q = q
beside_ p g q = Beside p g q
p <> q = beside_ p False q
p <+> q = beside_ p True q
beside :: Doc -> Bool -> RDoc -> RDoc
-- Specification: beside g p q = p <g> q
beside NoDoc g q = NoDoc
beside (p1 `Union` p2) g q = (beside p1 g q) `union_` (beside p2 g q)
beside Empty g q = q
beside (Nest k p) g q = nest_ k (beside p g q) -- p non-empty
beside p@(Beside p1 g1 q1) g2 q2
{- (A `op1` B) `op2` C == A `op1` (B `op2` C) iff op1 == op2
[ && (op1 == <> || op1 == <+>) ] -}
| g1 == g2 = beside p1 g1 (beside q1 g2 q2)
| otherwise = beside (reduceDoc p) g2 q2
beside p@(Above _ _ _) g q = beside (reduceDoc p) g q
beside (NilAbove p) g q = nilAbove_ (beside p g q)
beside (TextBeside s sl p) g q = textBeside_ s sl rest
where
rest = case p of
Empty -> nilBeside g q
other -> beside p g q
nilBeside :: Bool -> RDoc -> RDoc
-- Specification: text "" <> nilBeside g p
-- = text "" <g> p
nilBeside g Empty = Empty -- Hence the text "" in the spec
nilBeside g (Nest _ p) = nilBeside g p
nilBeside g p | g = textBeside_ space_text 1 p
| otherwise = p
-- ---------------------------------------------------------------------------
-- Separate, @sep@, Hughes version
-- Specification: sep ps = oneLiner (hsep ps)
-- `union`
-- vcat ps
sep = sepX True -- Separate with spaces
cat = sepX False -- Don't
sepX x [] = empty
sepX x (p:ps) = sep1 x (reduceDoc p) 0 ps
-- Specification: sep1 g k ys = sep (x : map (nest k) ys)
-- = oneLiner (x <g> nest k (hsep ys))
-- `union` x $$ nest k (vcat ys)
sep1 :: Bool -> RDoc -> Int -> [Doc] -> RDoc
sep1 g _ k ys | k `seq` False = undefined
sep1 g NoDoc k ys = NoDoc
sep1 g (p `Union` q) k ys = sep1 g p k ys
`union_`
(aboveNest q False k (reduceDoc (vcat ys)))
sep1 g Empty k ys = mkNest k (sepX g ys)
sep1 g (Nest n p) k ys = nest_ n (sep1 g p (k - n) ys)
sep1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (reduceDoc (vcat ys)))
sep1 g (TextBeside s sl p) k ys = textBeside_ s sl (sepNB g p (k - sl) ys)
-- Specification: sepNB p k ys = sep1 (text "" <> p) k ys
-- Called when we have already found some text in the first item
-- We have to eat up nests
sepNB g (Nest _ p) k ys = sepNB g p k ys
sepNB g Empty k ys = oneLiner (nilBeside g (reduceDoc rest))
`mkUnion`
nilAboveNest False k (reduceDoc (vcat ys))
where
rest | g = hsep ys
| otherwise = hcat ys
sepNB g p k ys = sep1 g p k ys
-- ---------------------------------------------------------------------------
-- @fill@
fsep = fill True
fcat = fill False
-- Specification:
-- fill [] = empty
-- fill [p] = p
-- fill (p1:p2:ps) = oneLiner p1 <#> nest (length p1)
-- (fill (oneLiner p2 : ps))
-- `union`
-- p1 $$ fill ps
fill g [] = empty
fill g (p:ps) = fill1 g (reduceDoc p) 0 ps
fill1 :: Bool -> RDoc -> Int -> [Doc] -> Doc
fill1 g _ k ys | k `seq` False = undefined
fill1 g NoDoc k ys = NoDoc
fill1 g (p `Union` q) k ys = fill1 g p k ys
`union_`
(aboveNest q False k (fill g ys))
fill1 g Empty k ys = mkNest k (fill g ys)
fill1 g (Nest n p) k ys = nest_ n (fill1 g p (k - n) ys)
fill1 g (NilAbove p) k ys = nilAbove_ (aboveNest p False k (fill g ys))
fill1 g (TextBeside s sl p) k ys = textBeside_ s sl (fillNB g p (k - sl) ys)
fillNB g _ k ys | k `seq` False = undefined
fillNB g (Nest _ p) k ys = fillNB g p k ys
fillNB g Empty k [] = Empty
fillNB g Empty k (y:ys) = nilBeside g (fill1 g (oneLiner (reduceDoc y)) k1 ys)
`mkUnion`
nilAboveNest False k (fill g (y:ys))
where
k1 | g = k - 1
| otherwise = k
fillNB g p k ys = fill1 g p k ys
-- ---------------------------------------------------------------------------
-- Selecting the best layout
best :: Mode
-> Int -- Line length
-> Int -- Ribbon length
-> RDoc
-> RDoc -- No unions in here!
best OneLineMode w r p
= get p
where
get Empty = Empty
get NoDoc = NoDoc
get (NilAbove p) = nilAbove_ (get p)
get (TextBeside s sl p) = textBeside_ s sl (get p)
get (Nest k p) = get p -- Elide nest
get (p `Union` q) = first (get p) (get q)
best mode w r p
= get w p
where
get :: Int -- (Remaining) width of line
-> Doc -> Doc
get w _ | w==0 && False = undefined
get w Empty = Empty
get w NoDoc = NoDoc
get w (NilAbove p) = nilAbove_ (get w p)
get w (TextBeside s sl p) = textBeside_ s sl (get1 w sl p)
get w (Nest k p) = nest_ k (get (w - k) p)
get w (p `Union` q) = nicest w r (get w p) (get w q)
get1 :: Int -- (Remaining) width of line
-> Int -- Amount of first line already eaten up
-> Doc -- This is an argument to TextBeside => eat Nests
-> Doc -- No unions in here!
get1 w _ _ | w==0 && False = undefined
get1 w sl Empty = Empty
get1 w sl NoDoc = NoDoc
get1 w sl (NilAbove p) = nilAbove_ (get (w - sl) p)
get1 w sl (TextBeside t tl p) = textBeside_ t tl (get1 w (sl + tl) p)
get1 w sl (Nest k p) = get1 w sl p
get1 w sl (p `Union` q) = nicest1 w r sl (get1 w sl p)
(get1 w sl q)
nicest w r p q = nicest1 w r 0 p q
nicest1 w r sl p q | fits ((w `minn` r) - sl) p = p
| otherwise = q
fits :: Int -- Space available
-> Doc
-> Bool -- True if *first line* of Doc fits in space available
fits n p | n < 0 = False
fits n NoDoc = False
fits n Empty = True
fits n (NilAbove _) = True
fits n (TextBeside _ sl p) = fits (n - sl) p
minn x y | x < y = x
| otherwise = y
-- @first@ and @nonEmptySet@ are similar to @nicest@ and @fits@, only simpler.
-- @first@ returns its first argument if it is non-empty, otherwise its second.
first p q | nonEmptySet p = p
| otherwise = q
nonEmptySet NoDoc = False
nonEmptySet (p `Union` q) = True
nonEmptySet Empty = True
nonEmptySet (NilAbove p) = True -- NoDoc always in first line
nonEmptySet (TextBeside _ _ p) = nonEmptySet p
nonEmptySet (Nest _ p) = nonEmptySet p
-- @oneLiner@ returns the one-line members of the given set of @Doc@s.
oneLiner :: Doc -> Doc
oneLiner NoDoc = NoDoc
oneLiner Empty = Empty
oneLiner (NilAbove p) = NoDoc
oneLiner (TextBeside s sl p) = textBeside_ s sl (oneLiner p)
oneLiner (Nest k p) = nest_ k (oneLiner p)
oneLiner (p `Union` q) = oneLiner p
-- ---------------------------------------------------------------------------
-- Displaying the best layout
renderStyle style doc
= fullRender (mode style)
(lineLength style)
(ribbonsPerLine style)
string_txt
""
doc
render doc = showDoc doc ""
showDoc doc rest = fullRender PageMode 100 1.5 string_txt rest doc
string_txt (Chr c) s = c:s
string_txt (Str s1) s2 = s1 ++ s2
string_txt (PStr s1) s2 = s1 ++ s2
fullRender OneLineMode _ _ txt end doc = easy_display space_text txt end (reduceDoc doc)
fullRender LeftMode _ _ txt end doc = easy_display nl_text txt end (reduceDoc doc)
fullRender mode line_length ribbons_per_line txt end doc
= display mode line_length ribbon_length txt end best_doc
where
best_doc = best mode hacked_line_length ribbon_length (reduceDoc doc)
hacked_line_length, ribbon_length :: Int
ribbon_length = round (fromIntegral line_length / ribbons_per_line)
hacked_line_length = case mode of { ZigZagMode -> maxBound; other -> line_length }
display mode page_width ribbon_width txt end doc
= case page_width - ribbon_width of { gap_width ->
case gap_width `quot` 2 of { shift ->
let
lay k _ | k `seq` False = undefined
lay k (Nest k1 p) = lay (k + k1) p
lay k Empty = end
lay k (NilAbove p) = nl_text `txt` lay k p
lay k (TextBeside s sl p)
= case mode of
ZigZagMode | k >= gap_width
-> nl_text `txt` (
Str (multi_ch shift '/') `txt` (
nl_text `txt` (
lay1 (k - shift) s sl p)))
| k < 0
-> nl_text `txt` (
Str (multi_ch shift '\\') `txt` (
nl_text `txt` (
lay1 (k + shift) s sl p )))
other -> lay1 k s sl p
lay1 k _ sl _ | k+sl `seq` False = undefined
lay1 k s sl p = Str (indent k) `txt` (s `txt` lay2 (k + sl) p)
lay2 k _ | k `seq` False = undefined
lay2 k (NilAbove p) = nl_text `txt` lay k p
lay2 k (TextBeside s sl p) = s `txt` (lay2 (k + sl) p)
lay2 k (Nest _ p) = lay2 k p
lay2 k Empty = end
in
lay 0 doc
}}
cant_fail = error "easy_display: NoDoc"
easy_display nl_text txt end doc
= lay doc cant_fail
where
lay NoDoc no_doc = no_doc
lay (Union p q) no_doc = {- lay p -} (lay q cant_fail) -- Second arg can't be NoDoc
lay (Nest k p) no_doc = lay p no_doc
lay Empty no_doc = end
lay (NilAbove p) no_doc = nl_text `txt` lay p cant_fail -- NoDoc always on first line
lay (TextBeside s sl p) no_doc = s `txt` lay p no_doc
-- OLD version: we shouldn't rely on tabs being 8 columns apart in the output.
-- indent n | n >= 8 = '\t' : indent (n - 8)
-- | otherwise = spaces n
indent n = spaces n
multi_ch 0 ch = ""
multi_ch n ch = ch : multi_ch (n - 1) ch
-- (spaces n) generates a list of n spaces
--
-- It should never be called with 'n' < 0, but that can happen for reasons I don't understand
-- Here's a test case:
-- ncat x y = nest 4 $ cat [ x, y ]
-- d1 = foldl1 ncat $ take 50 $ repeat $ char 'a'
-- d2 = parens $ sep [ d1, text "+" , d1 ]
-- main = print d2
-- I don't feel motivated enough to find the Real Bug, so meanwhile we just test for n<=0
spaces n | n <= 0 = ""
| otherwise = ' ' : spaces (n - 1)
{- Comments from Johannes Waldmann about what the problem might be:
In the example above, d2 and d1 are deeply nested, but `text "+"' is not,
so the layout function tries to "out-dent" it.
when I look at the Doc values that are generated, there are lots of
Nest constructors with negative arguments. see this sample output of
d1 (obtained with hugs, :s -u)
tBeside (TextDetails_Chr 'a') 1 Doc_Empty) (Doc_NilAbove (Doc_Nest
(-241) (Doc_TextBeside (TextDetails_Chr 'a') 1 Doc_Empty)))))
(Doc_NilAbove (Doc_Nest (-236) (Doc_TextBeside (TextDetails_Chr 'a') 1
(Doc_NilAbove (Doc_Nest (-5) (Doc_TextBeside (TextDetails_Chr 'a') 1
Doc_Empty)))))))) (Doc_NilAbove (Doc_Nest (-231) (Doc_TextBeside
(TextDetails_Chr 'a') 1 (Doc_NilAbove (Doc_Nest (-5) (Doc_TextBeside
(TextDetails_Chr 'a') 1 (Doc_NilAbove (Doc_Nest (-5) (Doc_TextBeside
(TextDetails_Chr 'a') 1 Doc_Empty))))))))))) (Doc_NilAbove (Doc_Nest
-}
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