drier-version.rb

class QueryParser < Whittle::Parser
  rule(:wsp => /\s+/).skip!

  rule("(")
  rule(")")

  rule("AND") % :left ^ 1
  rule("OR")  % :left ^ 1

  rule(">") % :left ^ 2
  rule("<") % :left ^ 2

  rule(:id  => /[a-zA-Z_][a-zA-Z0-9_]*/)

  rule(:int => /[0-9]+/)

  rule(:expr) do |r|
    r["(", :expr, ")"].as { |_, expr, _| expr }
    ["AND", "OR", ">", "<"].each do |op|
      r[:expr, op, :expr].as { |a, op, b| { :fname => op, :left => a, :right => b } }
    end
    r[:id]
    r[:int]
  end

  start(:expr)
end

pp QueryParser.new.parse("5 < 6 AND zip < button AND moon > spoon")

whittle8.rb

class QueryParser < Whittle::Parser
  rule(:wsp => /\s+/).skip!

  rule("(")
  rule(")")

  rule("AND") % :left ^ 1
  rule("OR")  % :left ^ 1

  rule(">") % :left ^ 2
  rule("<") % :left ^ 2

  rule(:id  => /[a-zA-Z_][a-zA-Z0-9_]*/)

  rule(:int => /[0-9]+/)

  rule(:expr) do |r|
    r["(", :expr, ")"].as { |_, expr, _| expr }
    r[:expr, "AND", :expr].as { |a, op, b| { :fname => "AND", :left => a, :right => b } }
    r[:expr, "OR", :expr].as { |a, op, b|  { :fname => "OR", :left => a, :right => b } }
    r[:expr, ">", :expr].as { |a, op, b|   { :fname => "GT", :left => a, :right => b } }
    r[:expr, "<", :expr].as { |a, op, b|   { :fname => "LT", :left => a, :right => b } }
    r[:id]
    r[:int]
  end

  start(:expr)
end

pp QueryParser.new.parse("5 < 6 AND zip < button AND moon > spoon")