DSL example

DSL.rb

require 'active_support'
require 'active_support/core_ext'

class Program

  class << self
    def define(&block)
      Program.new.tap { |p| p.instance_eval(&block) }
    end
  end

  attr_accessor :program_name, :program_acronym, :program_length
  attr_reader :routines

  def initialize
    @routines = []
  end

  alias_method :name, :program_name=
  alias_method :acronym, :program_acronym=
  alias_method :suggested_length, :program_length=

  def routine(&block)
    @routines << Routine.new.tap do |new_routine|
      new_routine.instance_eval(&block)
    end
  end
end

class Routine
  attr_accessor :routine_name
  attr_reader :exercises

  def initialize
    @exercises = {}
  end

  alias_method :name, :routine_name=

  def exercise(reference, &block)
    @exercises[reference] ||= Exercise.new.tap do |new_exercise|
      if block
        new_exercise.instance_eval(&block)
      end
    end
  end
end

class Exercise
  attr_accessor :exercise_name, :exercise_acronym
  attr_reader :exercise_sets, :increment_ranges

  def initialize
    @exercise_sets = []
    @increment_ranges = []
  end

  alias_method :name, :exercise_name=
  alias_method :acronym, :exercise_acronym=

  def sets(quantity, &block)
    quantity.times do
      @exercise_sets << ExerciseSet.new.tap do |set|
        set.instance_eval(&block)
      end
    end
  end

  def increment(attr={},&block)
    @increment_ranges << IncrementRange.new(attr[:range], attr[:unit]).tap do |range|
      range.instance_eval(&block)
    end
  end 
end

class ExerciseSet
  attr_accessor :set_reps
  alias_method :reps, :set_reps=
end

class IncrementRange
  attr_accessor :increment
  attr_reader :range, :unit

  def initialize(range, unit)
    @range = range
    @unit = unit
  end

  alias_method :increase, :increment=
end

dsl_example.rb

Program.define do
  name 'StrongLifts 5x5'
  acronym 'SL5x5'
  suggested_length 3.months

  routine do
    name 'Routine A'

    exercise :squat do
      name 'Squat'
      acronym 'SQ'

      sets 5 do
        reps 5
      end

      increment :range => (0..9999), :unit => :lbs do
        increase 5
      end
      increment :range => (0..9999), :unit => :kg do
        increase 2.5
      end
    end

    exercise :bench_press do
      name 'Bench Press'
      acronym 'BP'

      sets 5 do
        reps 5
      end
      
      increment :range => (0..9999), :unit => :lbs do
        increase 5
      end

      increment :range => (0..9999), :unit => :kgs do
        increase 2.5
      end
    end

    exercise :barbell_row do
      name 'Barbell Row'
      acronym 'BR'

      sets 5 do
        reps 5
      end
      
      increment :range => (0..9999), :unit => :lbs do
        increase 5
      end

      increment :range => (0..9999), :unit => :kgs do
        increase 2.5
      end
    end
  end

  routine do
    name 'Routine B'

    exercise :squat

    exercise :overhead_press do
      name 'Overhead Press'
      acronym 'OHP'

      sets 5 do
        reps 5
      end
      
      increment :range => (0..9999), :unit => :lbs do
        increase 5
      end

      increment :range => (0..9999), :unit => :kgs do
        increase 2.5
      end
    end

    exercise :deadlift do
      name 'Deadlift'
      acronym 'DL'

      sets 1 do
        reps 5
      end
      
      increment :range => (0..225), :unit => :lbs do
        increase 5
      end
      increment :range => (255..9999), :unit => :lbs do
        increase 2.5
      end

      increment :range => (0..100), :unit => :kgs do
        increase 2.5
      end
      increment :range => (100..9999), :unit => :kgs do
        increase 1.25
      end
    end
  end
end

Gemfile

source 'https://rubygems.org'

gem 'activesupport'
gem 'pry'