stdlib/prettyprint.rb
# frozen_string_literal: true
#
# 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 http://bugs.ruby-lang.org
#
# == References
# Christian Lindig, Strictly Pretty, March 2000,
# http://www.st.cs.uni-sb.de/~lindig/papers/#pretty
#
# Philip Wadler, A prettier printer, March 1998,
# http://homepages.inf.ed.ac.uk/wadler/topics/language-design.html#prettier
#
# == Author
# Tanaka Akira <akr@fsij.org>
#
class PrettyPrint
# This is a convenience method which is same as follows:
#
# begin
# q = PrettyPrint.new(output, maxwidth, newline, &genspace)
# ...
# q.flush
# output
# end
#
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
# 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+.
#
def PrettyPrint.singleline_format(output=''.dup, maxwidth=nil, newline=nil, genspace=nil)
q = SingleLine.new(output)
yield q
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.
#
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
# The output object.
#
# This defaults to '', and should accept the << method
attr_reader :output
# The maximum width of a line, before it is separated in to a newline
#
# This defaults to 79, and should be a Fixnum
attr_reader :maxwidth
# The value that is appended to +output+ to add a new line.
#
# This defaults to "\n", and should be String
attr_reader :newline
# 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}
attr_reader :genspace
# The number of spaces to be indented
attr_reader :indent
# The PrettyPrint::GroupQueue of groups in stack to be pretty printed
attr_reader :group_queue
# 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>
def current_group
@group_stack.last
end
# Breaks the buffer into lines that are shorter than #maxwidth
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 adds +obj+ as a text of +width+ columns in width.
#
# If +width+ is not specified, obj.length is used.
#
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
# 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.
#
def fill_breakable(sep=' ', width=sep.length)
group { breakable sep, width }
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.
#
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
# 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, <tt>text open_obj, open_width</tt> is called
# before grouping. If +close_obj+ is specified, <tt>text close_obj,
# close_width</tt> is called after grouping.
#
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.
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.
#
def nest(indent)
@indent += indent
begin
yield
ensure
@indent -= indent
end
end
# outputs buffered data.
#
def flush
@buffer.each {|data|
@output_width = data.output(@output, @output_width)
}
@buffer.clear
@buffer_width = 0
end
# The Text class is the means by which to collect strings from objects.
#
# This class is intended for internal use of the PrettyPrint buffers.
class Text # :nodoc:
# Creates a new text object.
#
# This constructor takes no arguments.
#
# The workflow is to append a PrettyPrint::Text object to the buffer, and
# being able to call the buffer.last() to reference it.
#
# As there are objects, use PrettyPrint::Text#add to include the objects
# and the width to utilized by the String version of this object.
def initialize
@objs = []
@width = 0
end
# The total width of the objects included in this Text object.
attr_reader :width
# Render the String text of the objects that have been added to this Text object.
#
# Output the text to +out+, and increment the width to +output_width+
def output(out, output_width)
@objs.each {|obj| out << obj}
output_width + @width
end
# Include +obj+ in the objects to be pretty printed, and increment
# this Text object's total width by +width+
def add(obj, width)
@objs << obj
@width += width
end
end
# The Breakable class is used for breaking up object information
#
# This class is intended for internal use of the PrettyPrint buffers.
class Breakable # :nodoc:
# Create a new Breakable object.
#
# Arguments:
# * +sep+ String of the separator
# * +width+ Fixnum width of the +sep+
# * +q+ parent PrettyPrint object, to base from
def initialize(sep, width, q)
@obj = sep
@width = width
@pp = q
@indent = q.indent
@group = q.current_group
@group.breakables.push self
end
# Holds the separator String
#
# The +sep+ argument from ::new
attr_reader :obj
# The width of +obj+ / +sep+
attr_reader :width
# The number of spaces to indent.
#
# This is inferred from +q+ within PrettyPrint, passed in ::new
attr_reader :indent
# Render the String text of the objects that have been added to this
# Breakable object.
#
# Output the text to +out+, and increment the width to +output_width+
def output(out, output_width)
@group.breakables.shift
if @group.break?
out << @pp.newline
out << @pp.genspace.call(@indent)
@indent
else
@pp.group_queue.delete @group if @group.breakables.empty?
out << @obj
output_width + @width
end
end
end
# The Group class is used for making indentation easier.
#
# While this class does neither the breaking into newlines nor indentation,
# it is used in a stack (as well as a queue) within PrettyPrint, to group
# objects.
#
# For information on using groups, see PrettyPrint#group
#
# This class is intended for internal use of the PrettyPrint buffers.
class Group # :nodoc:
# Create a Group object
#
# Arguments:
# * +depth+ - this group's relation to previous groups
def initialize(depth)
@depth = depth
@breakables = []
@break = false
end
# This group's relation to previous groups
attr_reader :depth
# Array to hold the Breakable objects for this Group
attr_reader :breakables
# Makes a break for this Group, and returns true
def break
@break = true
end
# Boolean of whether this Group has made a break
def break?
@break
end
# Boolean of whether this Group has been queried for being first
#
# This is used as a predicate, and ought to be called first.
def first?
if defined? @first
false
else
@first = false
true
end
end
end
# The GroupQueue class is used for managing the queue of Group to be pretty
# printed.
#
# This queue groups the Group objects, based on their depth.
#
# This class is intended for internal use of the PrettyPrint buffers.
class GroupQueue # :nodoc:
# Create a GroupQueue object
#
# Arguments:
# * +groups+ - one or more PrettyPrint::Group objects
def initialize(*groups)
@queue = []
groups.each {|g| enq g}
end
# Enqueue +group+
#
# This does not strictly append the group to the end of the queue,
# but instead adds it in line, base on the +group.depth+
def enq(group)
depth = group.depth
@queue << [] until depth < @queue.length
@queue[depth] << group
end
# Returns the outer group of the queue
def deq
@queue.each {|gs|
(gs.length-1).downto(0) {|i|
unless gs[i].breakables.empty?
group = gs.slice!(i, 1).first
group.break
return group
end
}
gs.each {|group| group.break}
gs.clear
}
return nil
end
# Remote +group+ from this queue
def delete(group)
@queue[group.depth].delete(group)
end
end
# PrettyPrint::SingleLine is used by PrettyPrint.singleline_format
#
# It is passed to be similar to a PrettyPrint object itself, by responding to:
# * #text
# * #breakable
# * #nest
# * #group
# * #flush
# * #first?
#
# but instead, the output has no line breaks
#
class SingleLine
# Create a PrettyPrint::SingleLine object
#
# Arguments:
# * +output+ - String (or similar) to store rendered text. Needs to respond to '<<'
# * +maxwidth+ - Argument position expected to be here for compatibility.
# This argument is a noop.
# * +newline+ - Argument position expected to be here for compatibility.
# This argument is a noop.
def initialize(output, maxwidth=nil, newline=nil)
@output = output
@first = [true]
end
# Add +obj+ to the text to be output.
#
# +width+ argument is here for compatibility. It is a noop argument.
def text(obj, width=nil)
@output << obj
end
# Appends +sep+ to the text to be output. By default +sep+ is ' '
#
# +width+ argument is here for compatibility. It is a noop argument.
def breakable(sep=' ', width=nil)
@output << sep
end
# Takes +indent+ arg, but does nothing with it.
#
# Yields to a block.
def nest(indent) # :nodoc:
yield
end
# Opens a block for grouping objects to be pretty printed.
#
# Arguments:
# * +indent+ - noop argument. Present for compatibility.
# * +open_obj+ - text appended before the &blok. Default is ''
# * +close_obj+ - text appended after the &blok. Default is ''
# * +open_width+ - noop argument. Present for compatibility.
# * +close_width+ - noop argument. Present for compatibility.
def group(indent=nil, open_obj='', close_obj='', open_width=nil, close_width=nil)
@first.push true
@output << open_obj
yield
@output << close_obj
@first.pop
end
# Method present for compatibility, but is a noop
def flush # :nodoc:
end
# This is used as a predicate, and ought to be called first.
def first?
result = @first[-1]
@first[-1] = false
result
end
end
end