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# 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?
#
# == 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@m17n.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='', 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='', 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='', 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
attr_reader :output, :maxwidth, :newline, :genspace
attr_reader :indent, :group_queue
def current_group
@group_stack.last
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.
#
def first?
warn "PrettyPrint#first? is obsoleted at 1.8.2."
current_group.first?
end
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
def fill_breakable(sep=' ', width=sep.length)
group { breakable sep, width }
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.
#
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
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
class Text
def initialize
@objs = []
@width = 0
end
attr_reader :width
def output(out, output_width)
@objs.each {|obj| out << obj}
output_width + @width
end
def add(obj, width)
@objs << obj
@width += width
end
end
class Breakable
def initialize(sep, width, q)
@obj = sep
@width = width
@pp = q
@indent = q.indent
@group = q.current_group
@group.breakables.push self
end
attr_reader :obj, :width, :indent
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
class Group
def initialize(depth)
@depth = depth
@breakables = []
@break = false
end
attr_reader :depth, :breakables
def break
@break = true
end
def break?
@break
end
def first?
if defined? @first
false
else
@first = false
true
end
end
end
class GroupQueue
def initialize(*groups)
@queue = []
groups.each {|g| enq g}
end
def enq(group)
depth = group.depth
@queue << [] until depth < @queue.length
@queue[depth] << group
end
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
def delete(group)
@queue[group.depth].delete(group)
end
end
class SingleLine
def initialize(output, maxwidth=nil, newline=nil)
@output = output
@first = [true]
end
def text(obj, width=nil)
@output << obj
end
def breakable(sep=' ', width=nil)
@output << sep
end
def nest(indent)
yield
end
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
def flush
end
def first?
result = @first[-1]
@first[-1] = false
result
end
end
end
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