whittle8.rb

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

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

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

  rule(">") % :left ^ 1
  rule("<") % :left ^ 1

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

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

  rule(:bool_op) do |r|
    r["AND"]
    r["OR"]
  end

  rule(:comp_op) do |r|
    r[">"].as { "GT" }
    r["<"].as { "LT" }
  end

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

  start(:expr)
end

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

# =>
# {:fname=>"AND",
# :left=>
#  {:fname=>"AND",
#   :left=>{:fname=>"LT", :left=>"5", :right=>"6"},
#   :right=>{:fname=>"LT", :left=>"zip", :right=>"button"}},
# :right=>{:fname=>"GT", :left=>"moon", :right=>"spoon"}}