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List intention expression

/ Published in: Ruby
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  1. require 'active_support/binding_of_caller'
  2.  
  3. class Intention
  4.   def initialize(value_expression, var, source)
  5.     @value_expression = value_expression
  6.     @var = var
  7.     @source = source
  8.   end
  9.  
  10.   def to_a(predicates, binding)
  11.     predicates << 'true'  if predicates == []
  12.     eval(<<-EOF, binding)
  13.       #@source.select {|#@var|  #{predicates.join('&&')} }.map do |#@var|
  14.         #@value_expression
  15.       end
  16.     EOF
  17.   end
  18. end
  19.  
  20. class String
  21.   def |(other)
  22.     raise  unless other =~ /^(.+)<-(.+)$/
  23.     Intention.new(self, $1, $2)
  24.   end
  25. end
  26.  
  27. class I
  28.   def self.[](intention, *predicates)
  29.     raise  unless  intention.instance_of?(Intention)
  30.     Binding.of_caller do |binding|
  31.       intention.to_a(predicates, binding)
  32.     end
  33.   end
  34. end
  35.  
  36. =begin Example
  37. xs = [10,30,3,-5,1,10,100,-60]
  38. p I['(x*2).abs' | 'x<-xs', 'x < 50']
  39. #=> [20, 60, 6, 10, 2, 20, 120]
  40.  
  41. def quicksort(x = nil, *xs)
  42.   return []  if x == nil
  43.   quicksort(*I['y' | 'y <- xs', 'y < x']) + [x] + quicksort(*I['y' | 'y <- xs', 'y >= x'])
  44. end
  45. p quicksort(*xs)
  46. #=> [-60, -5, 1, 3, 10, 10, 30, 100]
  47. =end

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