Refactor and simplify recipe DSL evaluation usages:

Remove most of recipe evaluation code in Recipe class, and rely on
Recipe::DSL to get evaluated recipes.

* Remove Recipe#evaluate call from CLI, rely on
  Recipe.evaluate_from_file to get the evaluated recipe;
* Implement Recipe.evaluate_from_file(filepath, env);
* Implement Recipe::DSL.evaluate(code, env);
* Remove code and filepath accessor on Recipe;
* Remove Recipe.from_file and Recipe#evaluate methods;
* Move task evaluations in Recipe::DSL#evaluate;
* Modify Recipe constructor so that it accepts tasks as argument.

lib/producer/core/cli.rb

@@ -12,7 +12,6 @@ module Producer
 
       def run!
         check_arguments!
-        recipe.evaluate(env)
         worker.process recipe.tasks
       end
 
@@ -25,7 +24,7 @@ module Producer
       end
 
       def recipe
-        @recipe ||= Recipe.from_file(@arguments.first)
+        @recipe ||= Recipe.evaluate_from_file(@arguments.first, env)
       end
 
       def worker

lib/producer/core/recipe.rb

@@ -1,22 +1,14 @@
 module Producer
   module Core
     class Recipe
-      attr_reader :code, :filepath, :tasks
+      attr_accessor :tasks
 
-      def self.from_file(filepath)
-        new(File.read(filepath), filepath)
+      def self.evaluate_from_file(filepath, env)
+        DSL.evaluate(File.read(filepath), env)
       end
 
-      def initialize(code, filepath = nil)
-        @code     = code
-        @filepath = filepath
-        @tasks    = []
-      end
-
-      def evaluate(env)
-        dsl = DSL.new(@code).evaluate(env)
-        dsl.tasks.map { |e| e.evaluate env }
-        @tasks = dsl.tasks
+      def initialize(tasks = [])
+        @tasks = tasks
       end
     end
   end

lib/producer/core/recipe/dsl.rb

@@ -4,6 +4,11 @@ module Producer
       class DSL
         attr_reader :tasks
 
+        def self.evaluate(code, env)
+          dsl = new(code).evaluate(env)
+          Recipe.new(dsl.tasks)
+        end
+
         def initialize(code = nil, &block)
           @code   = code
           @block  = block
@@ -17,6 +22,7 @@ module Producer
           else
             instance_eval &@block
           end
+          @tasks.each { |e| e.evaluate env }
           self
         end