{- |

Module : $Header$

Description : John Hughes's and Simon Peyton Jones's Pretty Printer

Combinators

Copyright : (c) Hughes, Peyton Jones, K. Luettich, C. Maeder 1996-2006

License : similar to LGPL, see HetCATS/LICENSE.txt or LIZENZ.txt

Maintainer : Christian.Maeder@dfki.de

Stability : provisional

Portability : portable

John Hughes's and Simon Peyton Jones's Pretty Printer Combinators

with modifications marked with 'added by KL'

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 "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 Common.Lib.Pretty (

-- * The document type

Doc, -- Abstract

-- * Primitive Documents

empty,

semi, comma, colon, space, equals,

lparen, rparen, lbrack, rbrack, lbrace, rbrace,

-- * Converting values into documents

text, char, ptext, sp_text,

int, integer, float, double, rational,

-- * Wrapping documents in delimiters

parens, brackets, braces, quotes, doubleQuotes,

-- * Combining documents

(<>), (<+>), 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,

renderStyle',

-- ** General rendering

fullRender,

Mode(..),

TextDetails(..)

) where

infixl 6 <>

infixl 6 <+>

infixl 5 $$, $+$

-- ---------------------------------------------------------------------------

-- The interface

-- The primitive Doc values

isEmpty :: Doc -> Bool; -- ^ Returns 'True' if the document is empty

empty :: Doc; -- ^ An empty document

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

text :: String -> Doc

ptext :: String -> Doc

-- added by KL

{- |

the conversion function @sp_text@ can be used for a special use of this

library. This function enables the possibility to use the rendering

alghorithms provided for rendering LaTeX with a proportional font. It

can also be abused because you can add text that has a zero width.

-}

sp_text :: Int -> String -> Doc

char :: Char -> Doc

int :: Int -> Doc

integer :: Integer -> Doc

float :: Float -> Doc

double :: Double -> Doc

rational :: Rational -> Doc

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

(<>) :: Doc -> Doc -> Doc; -- ^Beside

hcat :: [Doc] -> Doc; -- ^List version of '<>'

(<+>) :: Doc -> Doc -> Doc; -- ^Beside, separated by space

hsep :: [Doc] -> Doc; -- ^List version of '<+>'

($$) :: Doc -> Doc -> Doc; -- ^Above; if there is no

-- overlap it \"dovetails\" the two

($+$) :: Doc -> Doc -> Doc; -- ^Above, without dovetailing.

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 :: Int -> Doc -> Doc; -- ^ Nested

-- GHC-specific ones.

hang :: Doc -> Int -> Doc -> Doc -- ^ @hang d1 n d2 = sep [d1, nest n d2]@

punctuate :: Doc -> [Doc] -> [Doc]

-- ^ @punctuate p [d1, ... dn] = [d1 \<> p, d2 \<> p, ... dn-1 \<> p, dn]@

-- Displaying @Doc@ values.

instance Show Doc where

showsPrec = const showDoc

-- | 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=80, ribbonsPerLine=1.19@)

style :: Style

style = Style { lineLength = 80, ribbonsPerLine = 1.19, mode = PageMode }

-- maximum line length 80 with 67 printable chars (up to 13 indentation chars)

-- | 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 being 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 = text . show

integer = text . show

float = text . show

double = text . show

rational = text . show

-- 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 _ [] = []

punctuate p (a:ds) = go a 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

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

-- RDoc is a "reduced Doc", guaranteed not to have a top-level Above or Beside

type RDoc = Doc

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, nl_text :: TextDetails

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_ :: Doc -> Doc

nilAbove_ = NilAbove

-- Arg of a TextBeside is always an RDoc

textBeside_ :: TextDetails -> Int -> Doc -> Doc

textBeside_ = TextBeside

-- Arg of Nest is always an RDoc

nest_ :: Int -> Doc -> Doc

nest_ = Nest

-- Args of union are always RDocs

union_ :: Doc -> Doc -> Doc

union_ = Union

-- 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 d = case reduceDoc d of

Empty -> True

_ -> 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}

-- added by KL

sp_text sl s = case sl of {sl1 -> textBeside_ (PStr s) sl1 Empty}

nest k = mkNest k . reduceDoc -- Externally callable version

-- mkNest checks for Nest's invariant that it doesn't have an Empty inside it

mkNest :: Int -> Doc -> Doc

mkNest k _ | k `seq` False = error "Pretty.mkNest"

mkNest k (Nest k1 p) = mkNest (k + k1) p

mkNest _ NoDoc = NoDoc

mkNest _ Empty = Empty

mkNest 0 p = p -- Worth a try!

mkNest k p = nest_ k p

-- mkUnion checks for an empty document

mkUnion :: Doc -> Doc -> Doc

mkUnion Empty _ = Empty

mkUnion p q = p `union_` q

-- ---------------------------------------------------------------------------

-- Vertical composition @$$@

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 = error "Pretty.aboveNest"

aboveNest NoDoc _ _ _ = NoDoc

aboveNest (p1 `Union` p2) g k q = aboveNest p1 g k q `union_`

aboveNest p2 g k q

aboveNest Empty _ 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

_ -> aboveNest p g k1 q

aboveNest _ _ _ _ = error "Common.Lib.Pretty.aboveNest"

nilAboveNest :: Bool -> Int -> RDoc -> RDoc

-- Specification: text s <> nilaboveNest g k q

-- = text s <> (text "" $g$ nest k q)

nilAboveNest _ k _ | k `seq` False = error "Pretty.nilAboveNest"

nilAboveNest _ _ 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 (indent k)) k q

| otherwise -- Put them really above

= nilAbove_ (mkNest k q)

-- ---------------------------------------------------------------------------

-- Horizontal composition @<>@

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 _ _ = NoDoc

beside (p1 `Union` p2) g q = beside p1 g q `union_` beside p2 g q

beside Empty _ 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

_ -> beside p g q

nilBeside :: Bool -> RDoc -> RDoc

-- Specification: text "" <> nilBeside g p

-- = text "" <g> p

nilBeside _ 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 :: Bool -> [Doc] -> Doc

sepX _ [] = 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 _ _ k _ | k `seq` False = error "Pretty.sep1"

sep1 _ NoDoc _ _ = 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 _ (NilAbove p) k s = nilAbove_ (aboveNest p False k (reduceDoc (vcat s)))

sep1 g (TextBeside s sl p) k ys = textBeside_ s sl (sepNB g p (k - sl) ys)

sep1 _ _ _ _ = error "Pretty.sep1"

-- 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 :: Bool -> Doc -> Int -> [Doc] -> Doc

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 :: Bool -> [Doc] -> Doc

fill _ [] = empty

fill g (p:ps) = fill1 g (reduceDoc p) 0 ps

fill1 :: Bool -> RDoc -> Int -> [Doc] -> Doc

fill1 _ _ k _ | k `seq` False = error "Pretty.fill1"

fill1 _ NoDoc _ _ = 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)

fill1 _ _ _ _ = error "Pretty.fill1"

fillNB :: Bool -> Doc -> Int -> [Doc] -> Doc

fillNB _ _ k _ | k `seq` False = error "Pretty.fillNB"

fillNB g (Nest _ p) k s = fillNB g p k s

fillNB _ Empty _ [] = 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 _ _ 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 _ p) = get p -- Elide nest

get (p `Union` q) = first (get p) (get q)

get _ = error "Pretty.best.get"

best _ w' r p'

= get w' p'

where

get :: Int -- (Remaining) width of line

-> Doc -> Doc

get w _ | w == 0 && False = error "Pretty.hs"

get _ Empty = Empty

get _ 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)

get _ _ = error "Pretty.best.get2"

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 = error "Pretty.hs"

get1 _ _ Empty = Empty

get1 _ _ 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 _ p) = get1 w sl p

get1 w sl (p `Union` q) = nicest1 w r sl (get1 w sl p)

(get1 w sl q)

get1 _ _ _ = error "Pretty.best.get1"

nicest :: Int -> Int -> Doc -> Doc -> Doc

nicest w r = nicest1 w r 0

nicest1 :: Int -> Int -> Int -> Doc -> Doc -> Doc

nicest1 w r sl p q | fits ((w `minn` r) - sl) p = p

| otherwise = q

where minn x y | x < y = x

| otherwise = y

fits :: Int -- Space available

-> Doc

-> Bool -- True if *first line* of Doc fits in space available

fits n _ | n < 0 = False

fits _ NoDoc = False

fits _ Empty = True

fits _ (NilAbove _) = True

fits n (TextBeside _ sl p) = fits (n - sl) p

fits _ _ = error "Pretty.fits"

-- @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 :: Doc -> Doc -> Doc

first p q | nonEmptySet p = p

| otherwise = q

nonEmptySet :: Doc -> Bool

nonEmptySet NoDoc = False

nonEmptySet (_ `Union` _) = True

nonEmptySet Empty = True

nonEmptySet (NilAbove _) = True -- NoDoc always in first line

nonEmptySet (TextBeside _ _ p) = nonEmptySet p

nonEmptySet (Nest _ p) = nonEmptySet p

nonEmptySet _ = error "Pretty.nonEmptySet"

-- @oneLiner@ returns the one-line members of the given set of @Doc@s.

oneLiner :: Doc -> Doc

oneLiner NoDoc = NoDoc

oneLiner Empty = Empty

oneLiner (NilAbove _) = NoDoc

oneLiner (TextBeside s sl p) = textBeside_ s sl (oneLiner p)

oneLiner (Nest k p) = nest_ k (oneLiner p)

oneLiner (p `Union` _) = oneLiner p

oneLiner _ = error "Pretty.oneLiner"

-- ---------------------------------------------------------------------------

-- Displaying the best layout

renderStyle = renderStyle' ""

renderStyle' :: String -> Style -> Doc -> String

renderStyle' rest style'

= fullRender (mode style')

(lineLength style')

(ribbonsPerLine style')

string_txt

rest

render doc = showDoc doc ""

showDoc :: Doc -> String -> String

showDoc doc rest = renderStyle' rest style doc

string_txt :: TextDetails -> String -> String

string_txt t s2 = let s1 = textToStr t in case s2 of

'\n' : _ -> reverse (dropWhile (== ' ') $ reverse s1) ++ s2

_ -> s1 ++ s2

textToStr :: TextDetails -> String

textToStr t = case t of

Chr c -> [c]

Str s -> s

PStr s -> s

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

_ -> line_length

display :: Mode -> Int -> Int -> (TextDetails -> a -> a) -> a -> Doc -> a

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 = (error "Pretty.hs")

lay k (Nest k1 p) = lay (k + k1) p

lay _ 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 ))

_ -> lay1 k s sl p

lay _ _ = error "Pretty.lay"

lay1 k _ sl _ | k + sl `seq` False = error "Pretty.lay1"

lay1 k s sl p = Str (indent k) `txt` (s `txt` lay2 (k + sl) p)

lay2 k _ | k `seq` False = (error "Pretty.hs")

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 _ Empty = end

lay2 _ _ = error "Pretty.lay2"

in

lay 0 doc

}}

easy_display :: TextDetails -> (TextDetails -> a -> a) -> a -> Doc -> a

easy_display nl txt end doc

= lay doc cant_fail

where

cant_fail = error "easy_display: NoDoc"

lay NoDoc no_doc = no_doc

lay (Union _p q) _no_doc = lay q cant_fail

-- Second arg can't be NoDoc

lay (Nest _ p) no_doc = lay p no_doc

lay Empty _no_doc = end

lay (NilAbove p) _no_doc = nl `txt` lay p cant_fail

-- NoDoc always on first line

lay (TextBeside s _ p) no_doc = s `txt` lay p no_doc

lay _ _ = error "Pretty.easy_display.lay"

indent :: Int -> String

indent n = multi_ch n ' '

multi_ch :: Int -> Char -> String

multi_ch = replicate