Portability	portable
Stability	experimental
Maintainer	Hans Hoglund <hans@hanshoglund.se>
Safe Haskell	Safe-Inferred

Text.Pretty

Contents

The Pretty typeclass
The Printer type
Construction
Predicates on printers
Rendering printers

Description

This library was based on The Design of a Pretty-printing Library by Jeuring and Meijer.

Heavily modified by Simon Peyton Jones (December 1996).

Lightly modified by Hans Hoglund (October 2012).

Synopsis

The Pretty typeclass

class Pretty a whereSource

Class of types that can be pretty-printed.

The Pretty class is similar to Show, but converts values to Printers instead of Strings. A printer is essentially a string with some extra structural information such as length and indentation.

Note that the instances for primitive types, lists and tuples all satisfy

 (show . pretty) x == show x

Methods

pretty :: a -> Printer Source

Return a printer for the given value.

prettyList :: [a] -> Printer Source

The method prettyList is provided to allow the programmer to give a specialised way of printing lists of values. For example, this is used by the predefined Pretty instance of the Char type, where values of type String should be shown in double quotes, rather than between square brackets.

Instances

Pretty Char
Pretty Double
Pretty Float
Pretty Int
Pretty Integer
Pretty ()
Pretty Printer
Pretty a => Pretty [a]
(Pretty a, Integral a) => Pretty (Ratio a)
Pretty a => Pretty (Maybe a)
(Pretty a, Pretty b) => Pretty (a, b)

The Printer type

data Printer Source

The abstract type of printers.

Instances

Show Printer
IsString Printer
Monoid Printer
Semigroup Printer
Pretty Printer

Construction

Primitive types

char :: Char -> Printer Source

A printer of height and width 1, containing a literal character.

string :: String -> Printer Source

A printer of height 1 containing a literal string. string satisfies the following laws:

```
string s <> string t = string (s++t)
```
string "" <> x = x, if x non-empty

The side condition on the last law is necessary because string "" has height 1, while empty has no height.

sizedText :: Int -> String -> Printer Source

Some string with any width. (string s = sizedText (length s) s)

zeroWidthText :: String -> Printer Source

Some string, but without any width. Use for non-printing string such as a HTML or Latex tags

int :: Int -> Printer Source

integer :: Integer -> Printer Source

float :: Float -> Printer Source

double :: Double -> Printer Source

rational :: Rational -> Printer Source

Combinators

empty :: Printer Source

The empty printer, 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.

(<->) :: Printer -> Printer -> Printer Source

Beside. <> is associative, with identity empty.

(<+>) :: Printer -> Printer -> Printer Source

Beside, separated by space, unless one of the arguments is empty. <+> is associative, with identity empty.

hcat :: [Printer] -> Printer Source

List version of <>.

hsep :: [Printer] -> Printer Source

List version of <+>.

(</>) :: Printer -> Printer -> Printer Source

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:

    string "hi" </> nest 5 (string "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.

(<//>) :: Printer -> Printer -> Printer Source

Above, with no overlapping. <//> is associative, with identity empty.

vcat :: [Printer] -> Printer Source

List version of </>.

sep :: [Printer] -> Printer Source

Either hsep or vcat.

cat :: [Printer] -> Printer Source

Either hcat or vcat.

fsep :: [Printer] -> Printer Source

"Paragraph fill" version of sep.

fcat :: [Printer] -> Printer Source

"Paragraph fill" version of cat.

Wrapping and punctuation

wrap :: Char -> Char -> Printer -> Printer Source

Wrap printer in the given characters.

parens :: Printer -> Printer Source

Wrap printer in (...)

brackets :: Printer -> Printer Source

Wrap printer in [...]

braces :: Printer -> Printer Source

Wrap printer in {...}

quotes :: Printer -> Printer Source

Wrap printer in '...'

doubleQuotes :: Printer -> Printer Source

Wrap printer in "..."

nest :: Int -> Printer -> Printer Source

Nest (or indent) a printer 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 <>.

hang :: Printer -> Int -> Printer -> Printer Source

hang d1 n d2 = sep [d1, nest n d2]

sepBy :: Printer -> [Printer] -> Printer Source

Join with separator.

 sepBy q [x1,x2..xn] = x1 <> q <> x2 <> q .. xn.

initBy :: Printer -> [Printer] -> Printer Source

Join with initiator.

 initBy q [x1,x2..xn] = q <> x1 <> q <> x2 <> q .. xn.

termBy :: Printer -> [Printer] -> Printer Source

Join with terminator.

 termBy q [x1,x2..xn] = x1 <> q <> x2 <> q .. xn <> q.

sepByS :: Printer -> [Printer] -> Printer Source

Join with separator followed by space.

 sepByS q [x1,x2..xn] = x1 <> q <+> x2 <> q <+>.. xn.

initByS :: Printer -> [Printer] -> Printer Source

Join with initiator followed by space.

 initByS q [x1,x2..xn] = q <+> x1 <> q <+> x2 <> q <+> .. xn.

termByS :: Printer -> [Printer] -> Printer Source

Join with terminator followed by space.

 termByS q [x1,x2..xn] = x1 <> q <+> x2 <> q <+> .. xn <> q.

Predicates on printers

isEmpty :: Printer -> Bool Source

Returns True if the printer is empty

Rendering printers

runPrinter :: Printer -> String Source

Render the Printer to a String using the default Style.

data Mode Source

Rendering mode.

Constructors

PageMode	Normal
ZigZagMode	With zig-zag cuts
LeftMode	No indentation, infinitely long lines
OneLineMode	All on one line

data Style Source

A printing style.

Constructors

Style
Fields mode :: Mode The printing mode lineLength :: Int Length of line, in chars ribbonsPerLine :: Float Ratio of ribbon length to line length

style :: Style Source

The default style (mode=PageMode, lineLength=100, ribbonsPerLine=1.5).

runPrinterStyle :: Style -> Printer -> String Source

Render the Printer to a String using the given Style.