lambda_rover.rb

#!/usr/local/bin/ruby

print "Input /^\\d \\d [NSEW] [LMR]+$/: "
raise "Bad input" unless input = gets.chomp.match(/^(\d+)\s(\d+)\s([NSEW])\s([LMR]+)$/)

x, y, direction, moves = input[1].to_i, input[2].to_i, input[3], input[4]
compass = %w{ N E S W }
i = compass.index(direction)

fns = lambda { y+=1 }, lambda { x+=1 }, lambda { y-=1 }, lambda { x-=1 }
       
play = { "L" => lambda { fns[i-1] ? i-=1 : i=-1 },
         "R" => lambda { fns[i+1] ? i+=1 : i=0 },
         "M" => lambda { fns[i].call }}
          
moves.split("").map { |move| play[move] }.map &:call
puts "#{x} #{y} #{compass[i]}"