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|
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% %
% Frown --- An LALR(k) parser generator for Haskell 98 %
% Copyright (C) 2001-2005 Ralf Hinze %
% %
% This program is free software; you can redistribute it and/or modify %
% it under the terms of the GNU General Public License (version 2) as %
% published by the Free Software Foundation. %
% %
% This program is distributed in the hope that it will be useful, %
% but WITHOUT ANY WARRANTY; without even the implied warranty of %
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the %
% GNU General Public License for more details. %
% %
% You should have received a copy of the GNU General Public License %
% along with this program; see the file COPYING. If not, write to %
% the Free Software Foundation, Inc., 59 Temple Place - Suite 330, %
% Boston, MA 02111-1307, USA. %
% %
% Contact information %
% Email: Ralf Hinze <ralf@cs.uni-bonn.de> %
% Homepage: http://www.informatik.uni-bonn.de/~ralf/ %
% Paper mail: Dr. Ralf Hinze %
% Institut für Informatik III %
% Universität Bonn %
% Römerstraße 164 %
% 53117 Bonn, Germany %
% %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%-------------------------------= --------------------------------------------
\section{Pretty printing combinators}
%-------------------------------= --------------------------------------------
> module Prettier (
> Doc,
> -- primitive combinators
> empty, string, newline, (<>), nest, group, fillgroup, oneliner,
> -- derived combinators
> text, int, integer, float, double, char, sp, nl, (<+>), (</>),
> block, parens, brackets, braces, condParens, concat, stack, strip,
> intersperse, header,
> -- rendering a document
> Width, Style(Page, OneLine), render,
> Pretty(pretty, prettyPrec, prettyList) )
> where
> import Prelude hiding(concat)
Todo: add Jeff Lewis's |tab| and |indent| combinators (see email).
Todo: add ribbon width (maximum number of characters on a line).
Todo: add laws for |fillgroup| which satisfies |fillgroup (newline s)
= string s <||> newline s| (|group| breaks consistently whereas
|fillgroup| tries to fill the lines).
% - - - - - - - - - - - - - - - = - - - - - - - - - - - - - - - - - - - - - - -
\subsection{Interface}
% - - - - - - - - - - - - - - - = - - - - - - - - - - - - - - - - - - - - - - -
The type of documents.
< data Doc
Primitive combinators.
> empty :: Doc
> string :: String -> Doc
> newline :: String -> Doc
> infixr 6 <>
> (<>) :: Doc -> Doc -> Doc
> nest :: Int -> Doc -> Doc
> group :: Doc -> Doc
> fillgroup :: Doc -> Doc
> oneliner :: Doc -> Doc
The argument of |newline| is the replacement string if it is placed on
one line.
Derived combinators.
> text :: String -> Doc
> int :: Int -> Doc
> integer :: Integer -> Doc
> float :: Float -> Doc
> double :: Double -> Doc
> char :: Char -> Doc
> sp, nl :: Doc
> block :: Int -> Doc -> Doc
> infixr 6 <+>, </>
> (<+>), (</>) :: Doc -> Doc -> Doc
> parens, brackets, braces :: Doc -> Doc
> condParens :: Bool -> Doc -> Doc
> concat, stack, strip :: [Doc] -> Doc
> intersperse :: Doc -> [Doc] -> Doc
> header :: String -> Doc
Rendering a document.
> type Width = Int
> data Style = Page Width | OneLine
> render :: Style -> Doc -> String
A type class for pretty printing.
> class (Show a) => Pretty a where
> pretty :: a -> Doc
> prettyPrec :: Int -> a -> Doc
> prettyList :: [a] -> Doc
>
> pretty a = prettyPrec 0 a
> prettyPrec d a = string (showsPrec d a "")
> prettyList as = brackets ( -- or |fillgroup| instead of |group|?
> intersperse (char ',' <> nl) (map pretty as))
Note that the default methods are defined in terms of each
other. Hence the user must provide either |pretty| or |prettyPrec|.
Nearly all of the predefined types are declared instances of |Pretty|.
% - - - - - - - - - - - - - - - = - - - - - - - - - - - - - - - - - - - - - - -
\subsection{Axiomatisation}
% - - - - - - - - - - - - - - - = - - - - - - - - - - - - - - - - - - - - - - -
The following laws are adequate to reduce any document to the form
(here |<||>| denotes the union of documents):
\[
|d1 <||> cdots <||> dn|,
\]
where each |di| has the form
\[
|string s0 <> nest i1 (newline r1) <> string s1 <> cdots <> nest ik (newline rk) <> string sk|.
\]
Laws for |string|:
%
\begin{eqnarray}
|string ""| & = & |empty| \\
|string (s ++ t)| & = & |string s <> string t|
\end{eqnarray}
%
Laws for |nest|:
%
\begin{eqnarray}
|nest 0 d| & = & |d| \\
|nest (i + j) d| & = & |nest i (nest j d)| \\
|nest i empty| & = & |empty| \\
|nest i (string s)| & = & |string s| \\
|nest i (d1 <> d2)| & = & |nest i d1 <> nest i d2|
\end{eqnarray}
%
Definition of |group|:
%
\begin{eqnarray}
|group d| & = & |oneliner d <||> d|
\end{eqnarray}
%
Note that |<||>| is not accessible to the user.
Laws for |<||>|:
%
\begin{eqnarray}
|(d1 <||> d2) <> d3| & = & |(d1 <> d3) <||> (d2 <> d3)| \\
|d1 <> (d2 <||> d3)| & = & |(d1 <> d2) <||> (d1 <> d3)| \\
|nest i (d1 <||> d2)| & = & |nest i d1 <||> nest i d2|
\end{eqnarray}
%
Laws for |oneliner|:
%
\begin{eqnarray}
|oneliner empty| & = & |empty| \\
|oneliner (string s)| & = & |string s| \\
|oneliner (newline s)| & = & |string s| \\
|oneliner (d1 <> d2)| & = & |oneliner d1 <> oneliner d2| \\
|oneliner (nest i d)| & = & |oneliner d| \\
|oneliner (d1 <||> d2)| & = & |oneliner d1|
\end{eqnarray}
%
This implies, in particular, that |oneliner (group d) = oneliner d|.
% - - - - - - - - - - - - - - - = - - - - - - - - - - - - - - - - - - - - - - -
\subsection{Example uses}
% - - - - - - - - - - - - - - - = - - - - - - - - - - - - - - - - - - - - - - -
> {-
% - - - - - - - - - - - - - - - = - - - - - - - - - - - - - - - - - - - - - - -
\subsubsection{Terms}
% - - - - - - - - - - - - - - - = - - - - - - - - - - - - - - - - - - - - - - -
> data Term = Term String [Term]
> prTerm (Term n []) = string n
> prTerm (Term n ts) = parens (group (nest 2 (stack (string n : map prTerm ts))))
> szTerm (Term n ts) = length n + length ts + sum (map szTerm ts)
> mkTerm 0 i = Term (mkName i) []
> mkTerm (d+1) i = Term (mkName i) (map (mkTerm d) (randoms i))
> mkName i = [ 'x' | j <- [1..i] ]
> randoms i = [ i * j `mod` p | j <- [2 .. i `mod` p] ]
> where p = 7
> teststring w d i = render (Page w) (prTerm (mkTerm d i))
> testshow w d i = putStrLn (teststring w d i)
> test w d i = length (teststring w d i)
Pretty> test 60 8 3
11402
(377229 reductions, 640227 cells, 7 garbage collections)
Pretty> test 60 9 3
28253
(901055 reductions, 1519954 cells, 16 garbage collections)
% - - - - - - - - - - - - - - - = - - - - - - - - - - - - - - - - - - - - - - -
\subsubsection{C programs}
% - - - - - - - - - - - - - - - = - - - - - - - - - - - - - - - - - - - - - - -
General aestethic rule: to obtain nice indentation add a |nl|
before calling |pp| for a subcomponent or more general:
|pp (... e ...) = ... nl <> string s <> sp <> nest (length s + 1) (pp e)|.
> type Expr = String
>
> data Stat = Expr Expr -- expression statement
> | While Expr Stat -- iteration statement
> | If Expr Stat Stat -- selection statement
> | Block [Stat] -- compound statement
> | Return Expr -- jump statement
> ppExpr :: Expr -> Doc
> ppExpr e = string e
> ppStat :: Stat -> Doc
> ppStat (Expr e) = ppExpr e <> string ";"
> ppStat (While e s) = group (string "while" <+> parens (ppExpr e)
> <> nest 4 (nl <> ppStat s))
> ppStat (If e s1 s2) = group (string "if" <+> parens (ppExpr e)
> <> nest 4 (nl <> ppStat s1) <> nl
> <> string "else"
> <> nest 4 (nl <> ppStat s2))
> ppStat (Block ss) = group (string "{"
> <> nest 4 (concat [ nl <> ppStat s | s <- ss ]) <> nl
> <> string "}")
> ppStat (Return e) = string "return" <+> ppExpr e <> string ";"
> binsearch :: Stat
> binsearch =
> Block [
> Expr "low = 0",
> Expr "high = n - 1",
> While "low <= high" (
> Block [
> Expr "mid = (low + high) / 2",
> If "x < v[mid]" (
> Expr "high = mid - 1" ) (
> If "x > v[mid]" (
> Expr "low = mid + 1" ) (
> Return "mid" ))
> ]),
> Return "-1"
> ]
> -}
% - - - - - - - - - - - - - - - = - - - - - - - - - - - - - - - - - - - - - - -
\subsection{Implementation}
% - - - - - - - - - - - - - - - = - - - - - - - - - - - - - - - - - - - - - - -
> --instance Show Doc where
> -- show d = render (Page 79) d
% - - - - - - - - - - - - - - - = - - - - - - - - - - - - - - - - - - - - - - -
\subsubsection{Primitive functions}
% - - - - - - - - - - - - - - - = - - - - - - - - - - - - - - - - - - - - - - -
> infixr 6 :<>
>
> type Length = Int
> data Doc = Empty
> | Doc :<> Doc
> | Nest Int Doc
> | String Length String
> | Newline Length String
> | Group Doc
> | FillGroup Doc
> deriving (Show)
The length of the string is cached in |String| and |Newline|.
> empty = Empty
> (<>) = (:<>)
> nest = Nest
> string s = String (length s) s
> newline s = Newline (length s) s
> group = Group
> fillgroup = FillGroup
> oneliner Empty = Empty
> oneliner (d1 :<> d2) = oneliner d1 <> oneliner d2
> oneliner (Nest _i d) = oneliner d
> oneliner (String l s) = String l s
> oneliner (Newline l s) = String l s
> oneliner (Group d) = oneliner d
> oneliner (FillGroup d) = oneliner d
Simple documents.
> data Simple = Nil
> | StringApp Int String Simple
> | NestLineApp Int Simple
> layout :: Simple -> String
> layout Nil = ""
> layout (StringApp _l s d) = s ++ layout d
> layout (NestLineApp i d) = '\n' : replicate i ' ' ++ layout d
> fits :: Width -> Simple -> Bool
> fits w _d
> | w < 0 = False
> fits _w Nil = True
> fits w (StringApp l _s d) = fits (w - l) d
> fits _w (NestLineApp _i _d) = True
Nested documents.
> data Item = Std !Int Doc | Grp !Int Doc | Fill !Int Doc
TODO: |Grp| needs no |i| argument.
> best :: Width -> Int -> [Item] -> Simple
> best _w _k [] = Nil
> best w k (Std _i Empty : ds) = best w k ds
> best w k (Std i (d1 :<> d2) : ds) = best w k (Std i d1 : Std i d2 : ds)
> best w k (Std i (Nest j d) : ds) = best w k (Std (i + j) d : ds)
> best w k (Std _i (String l s) : ds) = StringApp l s (best w (k + l) ds)
> best w _k (Std i (Newline _l _s) : ds)= NestLineApp i (best w i ds)
> best w k (Std i (Group d) : ds) = better w k (best w k (Grp i d : ds))
> (best w k (Std i d : ds))
> best w k (Std i (FillGroup d) : ds) = best w k (Fill i d : ds)
The following equations correspond to the ones
above except for the two last ones.
> best w k (Grp _i Empty : ds) = best w k ds
> best w k (Grp i (d1 :<> d2) : ds) = best w k (Grp i d1 : Grp i d2 : ds)
> best w k (Grp i (Nest _j d) : ds) = best w k (Grp i d : ds)
> best w k (Grp _i (String l s) : ds) = StringApp l s (best w (k + l) ds)
> best w k (Grp _i (Newline l s) : ds) = StringApp l s (best w (k + l) ds)
> best w k (Grp i (Group d) : ds) = best w k (Grp i d : ds)
> best w k (Grp i (FillGroup d) : ds) = best w k (Grp i d : ds)
Again, the following equations correspond to the ones
above except for the two last ones.
> best w k (Fill _i Empty : ds) = best w k ds
> best w k (Fill i (d1 :<> d2) : ds) = best w k (Fill i d1 : Fill i d2 : ds)
> best w k (Fill i (Nest j d) : ds) = best w k (Fill (i + j) d : ds)
> best w k (Fill _i (String l s) : ds) = StringApp l s (best w (k + l) ds)
> best w k (Fill i (Newline l s) : ds) = better w k (StringApp l s (best w (k + l) ds))
> (NestLineApp i (best w i ds))
> best w k (Fill i (Group d) : ds) = better w k (best w k (Grp i d : ds))
> (best w k (Fill i d : ds))
> best w k (Fill i (FillGroup d) : ds) = best w k (Fill i d : ds)
Choosing between two layouts.
> better :: Width -> Int -> Simple -> Simple -> Simple
> better w k d1 d2 = if fits (w - k) d1 then d1 else d2
Rendering.
> render (Page w) d = layout (best w 0 [Std 0 d])
> render OneLine d = layout (best maxBound 0 [Grp 0 d])
% - - - - - - - - - - - - - - - = - - - - - - - - - - - - - - - - - - - - - - -
\subsubsection{Derived functions}
% - - - - - - - - - - - - - - - = - - - - - - - - - - - - - - - - - - - - - - -
> text = string
> int i = string (show i)
> integer i = string (show i)
> float f = string (show f)
> double d = string (show d)
> char c = string [c]
> nl = newline " "
> sp = string " "
> block i d = group (nest i d)
> parens d = block 1 (string "(" <> d <> string ")")
> brackets d = block 1 (string "[" <> d <> string "]")
> braces d = block 1 (string "{" <> d <> string "}")
> condParens False d = d
> condParens True d = parens d
> concat = foldr (<>) empty
> intersperse _sep [] = empty
> intersperse _sep [d] = d
> intersperse sep (d : ds@(_ : _)) = d <> sep <> intersperse sep ds
> d1 </> d2 = d1 <> nl <> d2
> d1 <+> d2 = d1 <> sp <> d2
> stack = foldr1 (</>)
> strip = foldr1 (<+>)
> header s = string s <> nl <> string (replicate (length s) '-') <> nl <> nl
% - - - - - - - - - - - - - - - = - - - - - - - - - - - - - - - - - - - - - - -
\subsubsection{Class instances}
% - - - - - - - - - - - - - - - = - - - - - - - - - - - - - - - - - - - - - - -
instance Show (a -> b) where
showsPrec _d _f = showString "<function>"
instance Pretty (a -> b)
> instance Pretty Bool
> instance Pretty Char where
> prettyList s = string (show s)
> instance Pretty Int
> instance Pretty Integer
> instance Pretty Float
> instance Pretty Double
> instance (Pretty a) => Pretty [a] where
> prettyPrec _d as = prettyList as
> instance Pretty ()
> instance (Pretty a, Pretty b) => Pretty (a, b) where
> prettyPrec _d (a, b) = parens (
> pretty a <> char ',' <> nl <>
> pretty b)
> instance (Pretty a, Pretty b, Pretty c) => Pretty (a, b, c) where
> prettyPrec _d (a, b, c) = parens (
> pretty a <> char ',' <> nl <>
> pretty b <> char ',' <> nl <>
> pretty c)
> instance (Pretty a, Pretty b, Pretty c, Pretty d) => Pretty (a, b, c, d) where
> prettyPrec _d (a, b, c, d)
> = parens (
> pretty a <> char ',' <> nl <>
> pretty b <> char ',' <> nl <>
> pretty c <> char ',' <> nl <>
> pretty d)
> instance (Pretty a, Pretty b, Pretty c, Pretty d, Pretty e)
> => Pretty (a, b, c, d, e) where
> prettyPrec _d (a, b, c, d, e)
> = parens (
> pretty a <> char ',' <> nl <>
> pretty b <> char ',' <> nl <>
> pretty c <> char ',' <> nl <>
> pretty d <> char ',' <> nl <>
> pretty e)
>
> instance (Pretty a) => Pretty (Maybe a) where
> prettyPrec _d Nothing = string "Nothing"
> prettyPrec d (Just a) = condParens (d > 9) (
> block 4 (string "Just" </> prettyPrec 10 a))
|
