Class: PrettyPrint

Inherits:
Object
  • Object
show all
Defined in:
lib/prettyprint.rb

Overview

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

  • PrettyPrint#breakable

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 <[email protected]>

Defined Under Namespace

Classes: Breakable, Group, GroupQueue, SingleLine, Text

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(output = ''.dup, maxwidth = 79, newline = "\n", &genspace) ⇒ PrettyPrint

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.


82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
# File 'lib/prettyprint.rb', line 82

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

Instance Attribute Details

#genspaceObject (readonly)

A lambda or Proc, that takes one argument, of a Fixnum, and returns the corresponding number of spaces.

By default this is:

lambda {|n| ' ' * n}

118
119
120
# File 'lib/prettyprint.rb', line 118

def genspace
  @genspace
end

#group_queueObject (readonly)

The PrettyPrint::GroupQueue of groups in stack to be pretty printed


124
125
126
# File 'lib/prettyprint.rb', line 124

def group_queue
  @group_queue
end

#indentObject (readonly)

The number of spaces to be indented


121
122
123
# File 'lib/prettyprint.rb', line 121

def indent
  @indent
end

#maxwidthObject (readonly)

The maximum width of a line, before it is separated in to a newline

This defaults to 79, and should be a Fixnum


106
107
108
# File 'lib/prettyprint.rb', line 106

def maxwidth
  @maxwidth
end

#newlineObject (readonly)

The value that is appended to output to add a new line.

This defaults to “n”, and should be String


111
112
113
# File 'lib/prettyprint.rb', line 111

def newline
  @newline
end

#outputObject (readonly)

The output object.

This defaults to '', and should accept the << method


101
102
103
# File 'lib/prettyprint.rb', line 101

def output
  @output
end

Class Method Details

.format(output = ''.dup, maxwidth = 79, newline = "\n", genspace = lambda {|n| ' ' * n}) {|q| ... } ⇒ Object

This is a convenience method which is same as follows:

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

Yields:

  • (q)

45
46
47
48
49
50
# File 'lib/prettyprint.rb', line 45

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

.singleline_format(output = ''.dup, maxwidth = nil, newline = nil, genspace = nil) {|q| ... } ⇒ Object

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.

Yields:

  • (q)

59
60
61
62
63
# File 'lib/prettyprint.rb', line 59

def PrettyPrint.singleline_format(output=''.dup, maxwidth=nil, newline=nil, genspace=nil)
  q = SingleLine.new(output)
  yield q
  output
end

Instance Method Details

#break_outmost_groupsObject

Breaks the buffer into lines that are shorter than #maxwidth


160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
# File 'lib/prettyprint.rb', line 160

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

#breakable(sep = ' ', width = sep.length) ⇒ Object

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.


224
225
226
227
228
229
230
231
232
233
234
235
236
237
# File 'lib/prettyprint.rb', line 224

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

#current_groupObject

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:[email protected]/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>

155
156
157
# File 'lib/prettyprint.rb', line 155

def current_group
  @group_stack.last
end

#fill_breakable(sep = ' ', width = sep.length) ⇒ Object

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.


212
213
214
# File 'lib/prettyprint.rb', line 212

def fill_breakable(sep=' ', width=sep.length)
  group { breakable sep, width }
end

#flushObject

outputs buffered data.


288
289
290
291
292
293
294
# File 'lib/prettyprint.rb', line 288

def flush
  @buffer.each {|data|
    @output_width = data.output(@output, @output_width)
  }
  @buffer.clear
  @buffer_width = 0
end

#group(indent = 0, open_obj = '', close_obj = '', open_width = open_obj.length, close_width = close_obj.length) ⇒ Object

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.


249
250
251
252
253
254
255
256
257
# File 'lib/prettyprint.rb', line 249

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

#group_subObject

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


260
261
262
263
264
265
266
267
268
269
270
271
272
# File 'lib/prettyprint.rb', line 260

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

#nest(indent) ⇒ Object

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


277
278
279
280
281
282
283
284
# File 'lib/prettyprint.rb', line 277

def nest(indent)
  @indent += indent
  begin
    yield
  ensure
    @indent -= indent
  end
end

#text(obj, width = obj.length) ⇒ Object

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

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


180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
# File 'lib/prettyprint.rb', line 180

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