Паттерны проектирования 6.2

Паттерн Интерпретатор.

Transcript

1. Паттерны проектирования часть 6.2
2. Интерпретатор Поведенческий шаблон проектирования, решающий часто встречающуюся, но подверженную изменениям, задачу.
3. Абстрактное синтаксическое дерево терминалы и нетерминалы
4. Интерпретатор
5. Интерпретатор require 'find' class Expression #... end class All < Expression def evaluate(dir) results= [] Find.find(dir) do |p| next unless File.file?(p) results << p end results end end
6. Интерпретатор class FileName < Expression def initialize(pattern) @pattern = pattern end def evaluate(dir) results= [] Find.find(dir) do |p| next unless File.file?(p) name = File.basename(p) results << p if File.fnmatch(@pattern, name) end results end end
7. Интерпретатор expr_all = All.new files = expr_all.evaluate('test_dir') expr_mp3 = FileName.new('*.mp3') mp3s = expr_mp3.evaluate('test_dir')
8. Интерпретатор class Bigger < Expression def initialize(size) @size = size end def evaluate(dir) results = [] Find.find(dir) do |p| next unless File.file?(p) results << p if( File.size(p) > @size) end results end end
9. Интерпретатор class Writable < Expression def evaluate(dir) results = [] Find.find(dir) do |p| next unless File.file?(p) results << p if( File.writable?(p) ) end results end end
10. Интерпретатор class Not < Expression def initialize(expression) @expression = expression end def evaluate(dir) All.new.evaluate(dir) - @expression.evaluate(dir) end end expr_not_writable = Not.new( Writable.new ) readonly_files = expr_not_writable.evaluate('test_dir') small_expr = Not.new( Bigger.new(1024) ) small_files = small_expr.evaluate('test_dir') not_mp3_expr = Not.new( FileName.new('*.mp3') ) not_mp3s = not_mp3_expr.evaluate('test_dir')
11. Интерпретатор class Or < Expression def initialize(expression1, expression2) @expression1 = expression1 @expression2 = expression2 end def evaluate(dir) result1 = @expression1.evaluate(dir) result2 = @expression2.evaluate(dir) (result1 + result2).sort.uniq end end big_or_mp3_expr = Or.new( Bigger.new(1024), FileName.new('*.mp3') ) big_or_mp3s = big_or_mp3_expr.evaluate('test_dir')
12. Интерпретатор class And < Expression def initialize(expression1, expression2) @expression1 = expression1 @expression2 = expression2 end def evaluate(dir) result1 = @expression1.evaluate(dir) result2 = @expression2.evaluate(dir) (result1 & result2) end end
13. Интерпретатор complex_expression = And.new( And.new(Bigger.new(1024), FileName.new('*.mp3')), Not.new(Writable.new )) complex_expression.evaluate('test_dir') complex_expression.evaluate('/tmp')
14. # and (and(bigger 1024)(filename *.mp3)) writable class Parser def initialize(text) @tokens = text.scan(/\(|\)|[\w\.\*]+/) end def next_token @tokens.shift end def expression token = next_token if token == nil return nil elsif token == '(' result = expression raise 'Expected )' unless next_token == ')' result elsif token == 'all' return All.new elsif token == 'writable' return Writable.new elsif token == 'bigger' return Bigger.new(next_token.to_i) elsif token == 'filename' return FileName.new(next_token) elsif token == 'not' return Not.new(expression) elsif token == 'and' return And.new(expression, expression) elsif token == 'or' return Or.new(expression, expression) else raise "Unexpected token: #{token}" end end
15. Интерпретатор parser = Parser.new "and (and(bigger 1024)(filename *.mp3)) writable" ast = parser.expression
16. Интерпретатор class Expression def |(other) Or.new(self, other) end def &(other) And.new(self, other) end end #Or.new( # And.new(Bigger.new(2000), Not.new(Writable.new)), # FileName.new('*.mp3')) (Bigger.new(2000) & Not.new(Writable.new)) | FileName.new("*.mp3")
17. Интерпретатор def all All.new end def bigger(size) Bigger.new(size) end def name(pattern) FileName.new(pattern) end def except(expression) Not.new(expression) end def writable Writable.new end # (bigger(2000) & except(writable) ) | file_name('*.mp3')