Exemplo de rake task numa abordagem Procedural |> Funcional (Rubyconf Brasil 2018)

Rakefile

ArgAsNumber = -> (args) do
  -> key { args[key].to_f }
end

CalculateTaskArgumentsWith = -> (operator) do
  -> (task, args) do
    arg_as_number = ArgAsNumber.(args)

    puts [:a, :b].map(&arg_as_number).reduce(&operator)
  end
end

desc 'adds two numbers'
task :sum, [:a, :b], &CalculateTaskArgumentsWith.(:+)

desc 'subtract two numbers.'
task :sub, [:a, :b], &CalculateTaskArgumentsWith.(:-)