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?
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@m17n.org>
Attributes
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/project/prettyprint.rb, line 41 def PrettyPrint.format(output='', 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/project/prettyprint.rb, line 78 def initialize(output='', 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/project/prettyprint.rb, line 55 def PrettyPrint.singleline_format(output='', maxwidth=nil, newline=nil, genspace=nil) q = SingleLine.new(output) yield q output end
Public Instance Methods
# File lib/project/prettyprint.rb, line 122 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 tells “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/project/prettyprint.rb, line 170 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
# File lib/project/prettyprint.rb, line 96 def current_group @group_stack.last end
# File lib/project/prettyprint.rb, line 158 def fill_breakable(sep=' ', width=sep.length) group { breakable sep, width } end
first? is a predicate to test the call is a first call to first? with current group.
It is useful to format comma separated values as:
q.group(1, '[', ']') { xxx.each {|yyy| unless q.first? q.text ',' q.breakable end ... pretty printing yyy ... } }
first? is obsoleted in 1.8.2.
# File lib/project/prettyprint.rb, line 117 def first? warn "PrettyPrint#first? is obsoleted at 1.8.2." current_group.first? end
outputs buffered data.
# File lib/project/prettyprint.rb, line 233 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/project/prettyprint.rb, line 195 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
# File lib/project/prettyprint.rb, line 205 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/project/prettyprint.rb, line 222 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/project/prettyprint.rb, line 142 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