This class implements a pretty printing algorithm. It finds line breaks and nice indentations for grouped structure.

By default, the class assumes that primitive elements are strings and each byte in the strings have single column in width. But it can be used for other situations by giving suitable arguments for some methods:

There are several candidate uses:

  • text formatting using proportional fonts

  • multibyte characters which has columns different to number of bytes

  • non-string formatting

Bugs

  • Box based formatting?

  • Other (better) model/algorithm?

Report any bugs at bugs.ruby-lang.org

References

Christian Lindig, Strictly Pretty, March 2000, www.st.cs.uni-sb.de/~lindig/papers/#pretty

Philip Wadler, A prettier printer, March 1998, homepages.inf.ed.ac.uk/wadler/topics/language-design.html#prettier

Author

Tanaka Akira <akr@fsij.org>


Class Methods


This is a convenience method which is same as follows:

begin
  q = PrettyPrint.new(output, maxwidth, newline, &genspace)
  ...
  q.flush
  output
end

Creates a buffer for pretty printing.

output is an output target. If it is not specified, '' is assumed. It should have a << method which accepts the first argument obj of PrettyPrint#text, the first argument sep of PrettyPrint#breakable, the first argument newline of PrettyPrint.new, and the result of a given block for PrettyPrint.new.

maxwidth specifies maximum line length. If it is not specified, 79 is assumed. However actual outputs may overflow maxwidth if long non-breakable texts are provided.

newline is used for line breaks. “n” is used if it is not specified.

The block is used to generate spaces. {|width| ' ' * width} is used if it is not given.

This is similar to PrettyPrint::format but the result has no breaks.

maxwidth, newline and genspace are ignored.

The invocation of breakable in the block doesn't break a line and is treated as just an invocation of text.

Instance Methods


Breaks the buffer into lines that are shorter than maxwidth

This says “you can break a line here if necessary”, and a width-column text sep is inserted if a line is not broken at the point.

If sep is not specified, “ ” is used.

If width is not specified, sep.length is used. You will have to specify this when sep is a multibyte character, for example.

Returns the group most recently added to the stack.

Contrived example:

out = ""
=> ""
q = PrettyPrint.new(out)
=> #<PrettyPrint:0x82f85c0 @output="", @maxwidth=79, @newline="\n", @genspace=#<Proc:0x82f8368@/home/vbatts/.rvm/rubies/ruby-head/lib/ruby/2.0.0/prettyprint.rb:82 (lambda)>, @output_width=0, @buffer_width=0, @buffer=[], @group_stack=[#<PrettyPrint::Group:0x82f8138 @depth=0, @breakables=[], @break=false>], @group_queue=#<PrettyPrint::GroupQueue:0x82fb7c0 @queue=[[#<PrettyPrint::Group:0x82f8138 @depth=0, @breakables=[], @break=false>]]>, @indent=0>
q.group {
  q.text q.current_group.inspect
  q.text q.newline
  q.group(q.current_group.depth + 1) {
    q.text q.current_group.inspect
    q.text q.newline
    q.group(q.current_group.depth + 1) {
      q.text q.current_group.inspect
      q.text q.newline
      q.group(q.current_group.depth + 1) {
        q.text q.current_group.inspect
        q.text q.newline
      }
    }
  }
}
=> 284
 puts out
#<PrettyPrint::Group:0x8354758 @depth=1, @breakables=[], @break=false>
#<PrettyPrint::Group:0x8354550 @depth=2, @breakables=[], @break=false>
#<PrettyPrint::Group:0x83541cc @depth=3, @breakables=[], @break=false>
#<PrettyPrint::Group:0x8347e54 @depth=4, @breakables=[], @break=false>

This is similar to breakable except the decision to break or not is determined individually.

Two fill_breakable under a group may cause 4 results: (break,break), (break,non-break), (non-break,break), (non-break,non-break). This is different to breakable because two breakable under a group may cause 2 results: (break,break), (non-break,non-break).

The text sep is inserted if a line is not broken at this point.

If sep is not specified, “ ” is used.

If width is not specified, sep.length is used. You will have to specify this when sep is a multibyte character, for example.

outputs buffered data.

Groups line break hints added in the block. The line break hints are all to be used or not.

If indent is specified, the method call is regarded as nested by nest(indent) { … }.

If open_obj is specified, text open_obj, open_width is called before grouping. If close_obj is specified, text close_obj, close_width is called after grouping.

Takes a block and queues a new group that is indented 1 level further.

Increases left margin after newline with indent for line breaks added in the block.

This adds obj as a text of width columns in width.

If width is not specified, obj.length is used.