"One of Factor's key features is the ability to print almost any object as a valid source literal expression. This greatly aids debugging and provides the building blocks for light-weight object serialization facilities."
"The prettyprinter has some limitations; namely, the following objects may not print in a readable form:"
{ $list
{ "When printing words, no " { $link POSTPONE: USE: } " declarations are output, hence the result may not be immediately readable without prefixing appropriate declarations." }
"Shared structure is not reflected in the printed output; if the output is parsed back in, fresh objects are created for all literal denotations."
{ "Circular structure is not printed in a readable way. Circular references print as " { $snippet "#" } "." }
"Floating point numbers might not equal themselves after being printed and read, since a decimal representation of a float is inexact."
}
"On a final note, the " { $link short. } ", " { $link pprint-short } " and " { $link unparse-short } " words restrict the length and nesting of printed sequences, their output will very likely not be valid syntax. They are only intended for interactive use." ;
ARTICLE: "prettyprint-variables" "Prettyprint control variables"
"The following variables affect the " { $link . } " and " { $link pprint } " words if set in the current dynamic scope:"
{ $subsection tab-size }
{ $subsection margin }
{ $subsection nesting-limit }
{ $subsection length-limit }
{ $subsection line-limit }
{ $subsection string-limit }
"Note that the " { $link short. } " and " { $link pprint-short } " variables override some of these variables."
{
$warning "Treat the global variables as essentially being constants. Only ever rebind them in a nested scope."
$terpri
"Some of the globals are safe to change, like the tab size and wrap margin. However setting limits globally could break code which uses the prettyprinter as a serialization mechanism."
} ;
ARTICLE: "prettyprint-extension" "Extending the prettyprinter"
"It is possible to define literal syntax for a new class using the " { $link "parser" } ", and then define a corresponding prettyprint method for the class which reproduces the literal syntax."
$terpri
"The prettyprinter maintains some internal state while prettyprinting. First, the object graph is traversed and a tree of " { $emphasis "sections" } " is produced. A section is either a text node or a " { $emphasis "block" } " which itself consists of sections."
$terpri
"Once the output is divided into sections, the tree is traversed and intelligent decisions are made about indentation and line breaks. If a block does not fit on the remainder of the current line, a newline is output before and after the block, and additional indentation is used when printing the block."
$terpri
"The following generic word is called to output a prettyprinting section for an object:"
{ $subsection pprint* }
"Two types of leaf sections:"
{ $subsection text }
{ $subsection newline }
"Nesting and denesting is done using three words. There are two words to denest a block; they vary in indentation policy:"
{ $subsection <block }
{ $subsection block> }
{ $subsection block; }
"Recall that since " { $link text } " sections take style hashtables as input, any type of formatted text can be output, including presentations. See " { $link "styles" } " to explore the possibility." ;
