*Task*

How to define pretty-print tables for use with GPP.

*Description*

The utility AsFixToAbox is a language-independent front-end for the pretty-print system GPP. Instantiated with a set of language specific _formatting rules_ it becomes a formatter for a specific language.

These formatting rules (or pretty-print rules) define mappings from language constructs (specified as SDF productions) to BOX expressions. BOX is a language independent markup language  to describe the intended layout of text. See [[http://www.cs.uu.nl/wiki/pub/Merijn/PaperPrettyPrinterForEveryOccasion/APrettyPrinterForEveryOccasion.pdf][this paper]] for more information about pretty-print tables and the BOX markup language.

Pretty-print entries are defined in an ordered sequence of pretty-print tables.
This ordering allows overruling of pretty-print entries by defining overruling entries in tables with higher precedence. 

*Examples*

A pretty-print entry for a language construct S1 S2 ... Sn -> S looks like:

 S1 S2 ... Sn -> S -- H [ _1 _2 ... _n]

This entry defines a horizontal formatting (because of the H operator). The BOX expressions corresponding to the formatted non-terminal symbols S1 S2 ... Sn are refered to using the numbered place holders _1 _2 ... _n

A more advanced example which defines a formatting for an `if-then-else' construct is depicted below:

 [
  "if" Cond "then" StatSeq "else" StatSeq "fi" -> Stat -- 
  V [ V is=3 [ H[ KW["if"] _1 KW["then"] 
		_2
		]
	V is=3 [ KW["else]"
		_3
		]
	KW["fi"]
	]
 ]

The following BOX operators are used in this example: `KW' to format keywords, `H' to layout boxes horizontally, and `V' to format sub-boxes vertically. Furthermore, the space option `is' is used to specify that the boxes in a vertical context should be indented to the right. This example defines that if-then-else constructs should be formatted as:

 if Cond then
	StatSeq
 else
	StatSeq
 fi


*See also*

GPP, HowToPrettyPrintAGrammar