Documentation

The class Out is the equivalent of Show

It provides conversion of values to pretty printable Pretty.Doc's.

Minimal complete definition: docPrec or doc.

Derived instances of Out have the following properties

• The result of docPrec is a syntactically correct Haskell expression containing only constants, given the fixity declarations in force at the point where the type is declared. It contains only the constructor names defined in the data type, parentheses, and spaces. When labelled constructor fields are used, braces, commas, field names, and equal signs are also used.
• If the constructor is defined to be an infix operator, then docPrec will produce infix applications of the constructor.
• the representation will be enclosed in parentheses if the precedence of the top-level constructor in x is less than d (associativity is ignored). Thus, if d is 0 then the result is never surrounded in parentheses; if d is 11 it is always surrounded in parentheses, unless it is an atomic expression.
• If the constructor is defined using record syntax, then docPrec will produce the record-syntax form, with the fields given in the same order as the original declaration.

For example, given the declarations

data Tree a =  Leaf a  |  Node (Tree a) (Tree a) deriving (Generic)

The derived instance of Out is equivalent to:

instance (Out a) => Out (Tree a) where
 
        docPrec d (Leaf m) = Pretty.sep $ wrapParens (d > appPrec) $
             text "Leaf" : [nest (constrLen + parenLen) (docPrec (appPrec+1) m)]
          where appPrec = 10
                constrLen = 5;
                parenLen = if(d > appPrec) then 1 else 0

        docPrec d (Node u v) = Pretty.sep $ wrapParens (d > appPrec) $
             text "Node" : 
             nest (constrLen + parenLen) (docPrec (appPrec+1) u) : 
             [nest (constrLen + parenLen) (docPrec (appPrec+1) v)]
          where appPrec = 10
                constrLen = 5
                parenLen = if(d > appPrec) then 1 else 0

The default Pretty Printer,

Equivalent to:

ppStyle defaultStyle

Where defaultStyle = (mode=PageMode, lineLength=80, ribbonsPerLine=1.5)

Semi-customizable pretty printer.

Equivalent to:

ppStyle customStyle

Where customStyle uses the specified line length, mode = PageMode and ribbonsPerLine = 1.

Customizable pretty printer.

Takes a user defined Style as a parameter and uses outputIO to obtain the result Equivalent to:

fullPP outputIO (putChar '\n')

The default pretty printer returning Strings

Equivalent to

prettyStyle defaultStyle

Where defaultStyle = (mode=PageMode, lineLength=80, ribbonsPerLine=1.5)

Semi-customizable pretty printer.

Equivalent to:

prettyStyle customStyle

Where customStyle uses the specified line length, mode = PageMode and ribbonsPerLine = 1.

Customizable pretty printer

Takes a user defined Style as a parameter and uses outputStr to obtain the result Equivalent to:

fullPP outputStr ""

fullPP is a fully customizable Pretty Printer

Every other pretty printer just gives some default values to fullPP

Representable types of kind *. This class is derivable in GHC with the DeriveGeneric flag on.

A Generic instance must satisfy the following laws:

from . to ≡ id
to . from ≡ id

Utility function that handles the text conversion for fullPP.

outputIO transforms the text into Strings and outputs it directly.

Utility function that handles the text conversion for fullPP.

outputStr just leaves the text as a String which is usefull if you want to further process the pretty printed result.