class PrettyPrint
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:
-
newline object and space generation block for
PrettyPrint.new -
optional width argument for
PrettyPrint#text
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, lindig.github.io/papers/strictly-pretty-2000.pdf
Philip Wadler, A prettier printer, March 1998, homepages.inf.ed.ac.uk/wadler/topics/language-design.html#prettier
Author¶ ↑
Tanaka Akira <akr@fsij.org>
Constants
- VERSION
Attributes
The PrettyPrint::GroupQueue of groups in stack to be pretty printed
The number of spaces to be indented
The maximum width of a line, before it is separated in to a newline
This defaults to 79, and should be an Integer
The value that is appended to output to add a new line.
This defaults to “n”, and should be String
The output object.
This defaults to ”, and should accept the << method
Public Class Methods
This is a convenience method which is same as follows:
begin q = PrettyPrint.new(output, maxwidth, newline, &genspace) ... q.flush output end
# File lib/prettyprint.rb, line 47 def PrettyPrint.format(output=''.dup, maxwidth=79, newline="\n", genspace=lambda {|n| ' ' * n}) q = PrettyPrint.new(output, maxwidth, newline, &genspace) yield q 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.
# File lib/prettyprint.rb, line 84 def initialize(output=''.dup, maxwidth=79, newline="\n", &genspace) @output = output @maxwidth = maxwidth @newline = newline @genspace = genspace || lambda {|n| ' ' * n} @output_width = 0 @buffer_width = 0 @buffer = [] root_group = Group.new(0) @group_stack = [root_group] @group_queue = GroupQueue.new(root_group) @indent = 0 end
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.
# File lib/prettyprint.rb, line 61 def PrettyPrint.singleline_format(output=''.dup, maxwidth=nil, newline=nil, genspace=nil) q = SingleLine.new(output) yield q output end
Public Instance Methods
Breaks the buffer into lines that are shorter than maxwidth
# File lib/prettyprint.rb, line 162 def break_outmost_groups while @maxwidth < @output_width + @buffer_width return unless group = @group_queue.deq until group.breakables.empty? data = @buffer.shift @output_width = data.output(@output, @output_width) @buffer_width -= data.width end while !@buffer.empty? && Text === @buffer.first text = @buffer.shift @output_width = text.output(@output, @output_width) @buffer_width -= text.width end end end
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.
# File lib/prettyprint.rb, line 226 def breakable(sep=' ', width=sep.length) group = @group_stack.last if group.break? flush @output << @newline @output << @genspace.call(@indent) @output_width = @indent @buffer_width = 0 else @buffer << Breakable.new(sep, width, self) @buffer_width += width break_outmost_groups end end
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>
# File lib/prettyprint.rb, line 157 def current_group @group_stack.last end
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.
# File lib/prettyprint.rb, line 214 def fill_breakable(sep=' ', width=sep.length) group { breakable sep, width } end
outputs buffered data.
# File lib/prettyprint.rb, line 290 def flush @buffer.each {|data| @output_width = data.output(@output, @output_width) } @buffer.clear @buffer_width = 0 end
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.
# File lib/prettyprint.rb, line 251 def group(indent=0, open_obj='', close_obj='', open_width=open_obj.length, close_width=close_obj.length) text open_obj, open_width group_sub { nest(indent) { yield } } text close_obj, close_width end
Takes a block and queues a new group that is indented 1 level further.
# File lib/prettyprint.rb, line 262 def group_sub group = Group.new(@group_stack.last.depth + 1) @group_stack.push group @group_queue.enq group begin yield ensure @group_stack.pop if group.breakables.empty? @group_queue.delete group end end end
Increases left margin after newline with indent for line breaks added in the block.
# File lib/prettyprint.rb, line 279 def nest(indent) @indent += indent begin yield ensure @indent -= indent end end
This adds obj as a text of width columns in width.
If width is not specified, obj.length is used.
# File lib/prettyprint.rb, line 182 def text(obj, width=obj.length) if @buffer.empty? @output << obj @output_width += width else text = @buffer.last unless Text === text text = Text.new @buffer << text end text.add(obj, width) @buffer_width += width break_outmost_groups end end