Lisp macros in Ruby.rb

# See "Lisp Macros in 20 Minutes"
# at http://www.slideshare.net/pcalcado/lisp-macros-in-20-minutes-featuring-clojure-presentation

# Ruby implementation var. 1 {
def from(names)
  keys, vals = [], []
  i = -1

  names.each do |name|
    r = yield name
    if r[:where]
      vals << r[:select]
      keys << r[:orderby]
    end
  end
  vals.sort_by { keys[i+=1] }
end
# }

# Use it like:
names = %w{Burke Connor Frank Everett Albert George Harris David}

query = from(names) do |n| {
  where:   n.length==5,
  orderby: n,
  select:  n.upcase}
end

puts query

puts

# Ruby implementation var. 2 {
def from(names, r)
  names.select! { |x| r[:where][x] }
  names.sort_by! { |x| r[:orderby][x] }
  names.map { |x| r[:select][x] }
end
# }

# Use it like:
names = %w{Burke Connor Frank Everett Albert George Harris David}

query = from(names,
             where:   -> x {x.length == 5},
             orderby: -> x {x},
             select:  -> x {x.upcase})
puts query

# File output: {
#BURKE
#DAVID
#FRANK

#BURKE
#DAVID
#FRANK
# }