path: root/lib/prettyprint.rb

# $Id$

=begin
= PrettyPrint
The class implements 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 situasions
by giving suitable arguments for some methods:
newline object and space generation block for (({PrettyPrint.new})),
optional width argument for (({PrettyPrint#text})),
(({PrettyPrint#breakable})), etc.
There are several candidates to use them:
text formatting using proportional fonts,
multibyte characters which has columns diffrent to number of bytes,
non-string formatting, etc.

== class methods
--- PrettyPrint.new([output[, maxwidth[, newline]]]) [{|width| ...}]
    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.

--- PrettyPrint.format([output[, maxwidth[, newline[, genspace]]]]) {|pp| ...}
    is a convenience method which is same as follows:

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

--- PrettyPrint.singleline_format([output[, maxwidth[, newline[, genspace]]]]) {|pp| ...}
    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
    treated as just an invocation of (({text})).

== methods
--- text(obj[, width])
    adds ((|obj|)) as a text of ((|width|)) columns in width.

    If ((|width|)) is not specified, (({((|obj|)).length})) is used.

--- breakable([sep[, width]])
    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.

--- nest(indent) {...}
    increases left margin after newline with ((|indent|)) for line breaks added
    in the block.

--- group([indent[, open_obj[, close_obj[, open_width[, close_width]]]]]) {...}
    groups line break hints added in the block.
    The line break hints are all to be breaked 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
    at first.
    If ((|close_obj|)) is specified, (({text close_obj, close_width})) is
    called at last.

--- flush
    outputs buffered data.

--- 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:

      pp.group(1, '[', ']') {
        xxx.each {|yyy|
          unless pp.first?
            pp.text ','
            pp.breakable
          end
          ... pretty printing yyy ...
        }
      }

== Bugs
* Box based formatting?  Other (better) model/algorithm?

== References
Christian Lindig, Strictly Pretty, March 2000,
((<URL:http://www.gaertner.de/~lindig/papers/strictly-pretty.html>))

Philip Wadler, A prettier printer, March 1998,
((<URL:http://www.research.avayalabs.com/user/wadler/topics/recent.html#prettier>))

== AUTHOR
Tanaka Akira <akr@m17n.org>
=end

class PrettyPrint
  def PrettyPrint.format(output='', maxwidth=79, newline="\n", genspace=lambda {|n| ' ' * n})
    pp = PrettyPrint.new(output, maxwidth, newline, &genspace)
    yield pp
    pp.flush
    output
  end

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

  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

  def first?
    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

  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

  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

  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

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

  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, pp)
      @obj = sep
      @width = width
      @pp = pp
      @indent = pp.indent
      @group = pp.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

if __FILE__ == $0
  require 'test/unit'

  class WadlerExample < Test::Unit::TestCase
    def setup
      @tree = Tree.new("aaaa", Tree.new("bbbbb", Tree.new("ccc"),
                                                 Tree.new("dd")),
                               Tree.new("eee"),
                               Tree.new("ffff", Tree.new("gg"),
                                                Tree.new("hhh"),
                                                Tree.new("ii")))
    end

    def hello(width)
      PrettyPrint.format('', width) {|hello|
        hello.group {
          hello.group {
            hello.group {
              hello.group {
                hello.text 'hello'
                hello.breakable; hello.text 'a'
              }
              hello.breakable; hello.text 'b'
            }
            hello.breakable; hello.text 'c'
          }
          hello.breakable; hello.text 'd'
        }
      }
    end

    def test_hello_00_06
      expected = <<'End'.chomp
hello
a
b
c
d
End
      assert_equal(expected, hello(0))
      assert_equal(expected, hello(6))
    end

    def test_hello_07_08
      expected = <<'End'.chomp
hello a
b
c
d
End
      assert_equal(expected, hello(7))
      assert_equal(expected, hello(8))
    end

    def test_hello_09_10
      expected = <<'End'.chomp
hello a b
c
d
End
      out = hello(9); assert_equal(expected, out)
      out = hello(10); assert_equal(expected, out)
    end

    def test_hello_11_12
      expected = <<'End'.chomp
hello a b c
d
End
      assert_equal(expected, hello(11))
      assert_equal(expected, hello(12))
    end

    def test_hello_13
      expected = <<'End'.chomp
hello a b c d
End
      assert_equal(expected, hello(13))
    end

    def tree(width)
      PrettyPrint.format('', width) {|pp| @tree.show(pp)}
    end

    def test_tree_00_19
      expected = <<'End'.chomp
aaaa[bbbbb[ccc,
           dd],
     eee,
     ffff[gg,
          hhh,
          ii]]
End
      assert_equal(expected, tree(0))
      assert_equal(expected, tree(19))
    end

    def test_tree_20_22
      expected = <<'End'.chomp
aaaa[bbbbb[ccc, dd],
     eee,
     ffff[gg,
          hhh,
          ii]]
End
      assert_equal(expected, tree(20))
      assert_equal(expected, tree(22))
    end

    def test_tree_23_43
      expected = <<'End'.chomp
aaaa[bbbbb[ccc, dd],
     eee,
     ffff[gg, hhh, ii]]
End
      assert_equal(expected, tree(23))
      assert_equal(expected, tree(43))
    end

    def test_tree_44
      assert_equal(<<'End'.chomp, tree(44))
aaaa[bbbbb[ccc, dd], eee, ffff[gg, hhh, ii]]
End
    end

    def tree_alt(width)
      PrettyPrint.format('', width) {|pp| @tree.altshow(pp)}
    end

    def test_tree_alt_00_18
      expected = <<'End'.chomp
aaaa[
  bbbbb[
    ccc,
    dd
  ],
  eee,
  ffff[
    gg,
    hhh,
    ii
  ]
]
End
      assert_equal(expected, tree_alt(0))
      assert_equal(expected, tree_alt(18))
    end

    def test_tree_alt_19_20
      expected = <<'End'.chomp
aaaa[
  bbbbb[ ccc, dd ],
  eee,
  ffff[
    gg,
    hhh,
    ii
  ]
]
End
      assert_equal(expected, tree_alt(19))
      assert_equal(expected, tree_alt(20))
    end

    def test_tree_alt_20_49
      expected = <<'End'.chomp
aaaa[
  bbbbb[ ccc, dd ],
  eee,
  ffff[ gg, hhh, ii ]
]
End
      assert_equal(expected, tree_alt(21))
      assert_equal(expected, tree_alt(49))
    end

    def test_tree_alt_50
      expected = <<'End'.chomp
aaaa[ bbbbb[ ccc, dd ], eee, ffff[ gg, hhh, ii ] ]
End
      assert_equal(expected, tree_alt(50))
    end

    class Tree
      def initialize(string, *children)
        @string = string
        @children = children
      end

      def show(pp)
        pp.group {
          pp.text @string
          pp.nest(@string.length) {
            unless @children.empty?
              pp.text '['
              pp.nest(1) {
                first = true
                @children.each {|t|
                  if first
                    first = false
                  else
                    pp.text ','
                    pp.breakable
                  end
                  t.show(pp)
                }
              }
              pp.text ']'
            end
          }
        }
      end

      def altshow(pp)
        pp.group {
          pp.text @string
          unless @children.empty?
            pp.text '['
            pp.nest(2) {
              pp.breakable
              first = true
              @children.each {|t|
                if first
                  first = false
                else
                  pp.text ','
                  pp.breakable
                end
                t.altshow(pp)
              }
            }
            pp.breakable
            pp.text ']'
          end
        }
      end

    end
  end

  class StrictPrettyExample < Test::Unit::TestCase
    def prog(width)
      PrettyPrint.format('', width) {|pp|
        pp.group {
          pp.group {pp.nest(2) {
                       pp.text "if"; pp.breakable;
                       pp.group {
                         pp.nest(2) {
                           pp.group {pp.text "a"; pp.breakable; pp.text "=="}
                           pp.breakable; pp.text "b"}}}}
          pp.breakable
          pp.group {pp.nest(2) {
                       pp.text "then"; pp.breakable;
                       pp.group {
                         pp.nest(2) {
                           pp.group {pp.text "a"; pp.breakable; pp.text "<<"}
                           pp.breakable; pp.text "2"}}}}
          pp.breakable
          pp.group {pp.nest(2) {
                       pp.text "else"; pp.breakable;
                       pp.group {
                         pp.nest(2) {
                           pp.group {pp.text "a"; pp.breakable; pp.text "+"}
                           pp.breakable; pp.text "b"}}}}}
      }
    end

    def test_00_04
      expected = <<'End'.chomp
if
  a
    ==
    b
then
  a
    <<
    2
else
  a
    +
    b
End
      assert_equal(expected, prog(0))
      assert_equal(expected, prog(4))
    end

    def test_05
      expected = <<'End'.chomp
if
  a
    ==
    b
then
  a
    <<
    2
else
  a +
    b
End
      assert_equal(expected, prog(5))
    end

    def test_06
      expected = <<'End'.chomp
if
  a ==
    b
then
  a <<
    2
else
  a +
    b
End
      assert_equal(expected, prog(6))
    end

    def test_07
      expected = <<'End'.chomp
if
  a ==
    b
then
  a <<
    2
else
  a + b
End
      assert_equal(expected, prog(7))
    end

    def test_08
      expected = <<'End'.chomp
if
  a == b
then
  a << 2
else
  a + b
End
      assert_equal(expected, prog(8))
    end

    def test_09
      expected = <<'End'.chomp
if a == b
then
  a << 2
else
  a + b
End
      assert_equal(expected, prog(9))
    end

    def test_10
      expected = <<'End'.chomp
if a == b
then
  a << 2
else a + b
End
      assert_equal(expected, prog(10))
    end

    def test_11_31
      expected = <<'End'.chomp
if a == b
then a << 2
else a + b
End
      assert_equal(expected, prog(11))
      assert_equal(expected, prog(15))
      assert_equal(expected, prog(31))
    end

    def test_32
      expected = <<'End'.chomp
if a == b then a << 2 else a + b
End
      assert_equal(expected, prog(32))
    end

  end

  class TailGroup < Test::Unit::TestCase
    def test_1
      out = PrettyPrint.format('', 10) {|pp|
        pp.group {
          pp.group {
            pp.text "abc"
            pp.breakable
            pp.text "def"
          }
          pp.group {
            pp.text "ghi"
            pp.breakable
            pp.text "jkl"
          }
        }
      }
      assert_equal("abc defghi\njkl", out)
    end
  end

  class NonString < Test::Unit::TestCase
    def format(width)
      PrettyPrint.format([], width, 'newline', lambda {|n| "#{n} spaces"}) {|pp|
        pp.text(3, 3)
        pp.breakable(1, 1)
        pp.text(3, 3)
      }
    end

    def test_6
      assert_equal([3, "newline", "0 spaces", 3], format(6))
    end

    def test_7
      assert_equal([3, 1, 3], format(7))
    end

  end

  class Fill < Test::Unit::TestCase
    def format(width)
      PrettyPrint.format('', width) {|pp|
        pp.group {
          pp.text 'abc'
          pp.fill_breakable
          pp.text 'def'
          pp.fill_breakable
          pp.text 'ghi'
          pp.fill_breakable
          pp.text 'jkl'
          pp.fill_breakable
          pp.text 'mno'
          pp.fill_breakable
          pp.text 'pqr'
          pp.fill_breakable
          pp.text 'stu'
        }
      }
    end

    def test_00_06
      expected = <<'End'.chomp
abc
def
ghi
jkl
mno
pqr
stu
End
      assert_equal(expected, format(0))
      assert_equal(expected, format(6))
    end

    def test_07_10
      expected = <<'End'.chomp
abc def
ghi jkl
mno pqr
stu
End
      assert_equal(expected, format(7))
      assert_equal(expected, format(10))
    end

    def test_11_14
      expected = <<'End'.chomp
abc def ghi
jkl mno pqr
stu
End
      assert_equal(expected, format(11))
      assert_equal(expected, format(14))
    end

    def test_15_18
      expected = <<'End'.chomp
abc def ghi jkl
mno pqr stu
End
      assert_equal(expected, format(15))
      assert_equal(expected, format(18))
    end

    def test_19_22
      expected = <<'End'.chomp
abc def ghi jkl mno
pqr stu
End
      assert_equal(expected, format(19))
      assert_equal(expected, format(22))
    end

    def test_23_26
      expected = <<'End'.chomp
abc def ghi jkl mno pqr
stu
End
      assert_equal(expected, format(23))
      assert_equal(expected, format(26))
    end

    def test_27
      expected = <<'End'.chomp
abc def ghi jkl mno pqr stu
End
      assert_equal(expected, format(27))
    end

  end
end