Class | PrettyPrint |
In: |
lib/prettyprint.rb
|
Parent: | Object |
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:
There are several candidate uses:
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
Tanaka Akira <akr@m17n.org>
genspace | [R] | |
group_queue | [R] | |
indent | [R] | |
maxwidth | [R] | |
newline | [R] | |
output | [R] |
This is a convenience method which is same as follows:
begin q = PrettyPrint.new(output, maxwidth, newline, &genspace) ... q.flush output end
# File lib/prettyprint.rb, line 43 43: def PrettyPrint.format(output='', maxwidth=79, newline="\n", genspace=lambda {|n| ' ' * n}) 44: q = PrettyPrint.new(output, maxwidth, newline, &genspace) 45: yield q 46: q.flush 47: output 48: 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/prettyprint.rb, line 80 80: def initialize(output='', maxwidth=79, newline="\n", &genspace) 81: @output = output 82: @maxwidth = maxwidth 83: @newline = newline 84: @genspace = genspace || lambda {|n| ' ' * n} 85: 86: @output_width = 0 87: @buffer_width = 0 88: @buffer = [] 89: 90: root_group = Group.new(0) 91: @group_stack = [root_group] 92: @group_queue = GroupQueue.new(root_group) 93: @indent = 0 94: 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/prettyprint.rb, line 57 57: def PrettyPrint.singleline_format(output='', maxwidth=nil, newline=nil, genspace=nil) 58: q = SingleLine.new(output) 59: yield q 60: output 61: end
# File lib/prettyprint.rb, line 124 124: def break_outmost_groups 125: while @maxwidth < @output_width + @buffer_width 126: return unless group = @group_queue.deq 127: until group.breakables.empty? 128: data = @buffer.shift 129: @output_width = data.output(@output, @output_width) 130: @buffer_width -= data.width 131: end 132: while !@buffer.empty? && Text === @buffer.first 133: text = @buffer.shift 134: @output_width = text.output(@output, @output_width) 135: @buffer_width -= text.width 136: end 137: end 138: 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/prettyprint.rb, line 172 172: def breakable(sep=' ', width=sep.length) 173: group = @group_stack.last 174: if group.break? 175: flush 176: @output << @newline 177: @output << @genspace.call(@indent) 178: @output_width = @indent 179: @buffer_width = 0 180: else 181: @buffer << Breakable.new(sep, width, self) 182: @buffer_width += width 183: break_outmost_groups 184: end 185: end
# File lib/prettyprint.rb, line 160 160: def fill_breakable(sep=' ', width=sep.length) 161: group { breakable sep, width } 162: 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/prettyprint.rb, line 119 119: def first? 120: warn "PrettyPrint#first? is obsoleted at 1.8.2." 121: current_group.first? 122: end
outputs buffered data.
# File lib/prettyprint.rb, line 235 235: def flush 236: @buffer.each {|data| 237: @output_width = data.output(@output, @output_width) 238: } 239: @buffer.clear 240: @buffer_width = 0 241: 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/prettyprint.rb, line 197 197: def group(indent=0, open_obj='', close_obj='', open_width=open_obj.length, close_width=close_obj.length) 198: text open_obj, open_width 199: group_sub { 200: nest(indent) { 201: yield 202: } 203: } 204: text close_obj, close_width 205: end
# File lib/prettyprint.rb, line 207 207: def group_sub 208: group = Group.new(@group_stack.last.depth + 1) 209: @group_stack.push group 210: @group_queue.enq group 211: begin 212: yield 213: ensure 214: @group_stack.pop 215: if group.breakables.empty? 216: @group_queue.delete group 217: end 218: end 219: end
Increases left margin after newline with indent for line breaks added in the block.
# File lib/prettyprint.rb, line 224 224: def nest(indent) 225: @indent += indent 226: begin 227: yield 228: ensure 229: @indent -= indent 230: end 231: end
This adds obj as a text of width columns in width.
If width is not specified, obj.length is used.
# File lib/prettyprint.rb, line 144 144: def text(obj, width=obj.length) 145: if @buffer.empty? 146: @output << obj 147: @output_width += width 148: else 149: text = @buffer.last 150: unless Text === text 151: text = Text.new 152: @buffer << text 153: end 154: text.add(obj, width) 155: @buffer_width += width 156: break_outmost_groups 157: end 158: end