lib/rumonade/monad.rb in rumonade-0.4.2 vs lib/rumonade/monad.rb in rumonade-0.4.3

@@ -55,13 +55,19 @@
     #   [Some(Some(1)), Some(Some(None))], [None]].flatten
     #   #=> [1]
     #
     def flatten_with_monad(depth=nil)
       if depth.is_a? Integer
-        depth.times.inject(self) {|e, _| e.shallow_flatten }
+        depth.times.inject(self) { |e, _| e.shallow_flatten }
       else
-        bind { |x| x.is_a?(Monad) ? x.flatten_with_monad : self.class.unit(x) }
+        bind do |x|
+          if x.is_a?(Monad) && x.can_flatten_in_monad?
+            x.flatten_with_monad
+          else
+            self.class.unit(x)
+          end
+        end
       end
     end
 
     # Returns a monad whose elements are all those elements of this monad for which the given predicate returned true
     def select(lam = nil, &blk)
@@ -82,8 +88,16 @@
     #   [1, None].shallow_flatten
     #   #=> [1]
     #
     def shallow_flatten
       bind { |x| x.is_a?(Monad) ? x : self.class.unit(x) }
+    end
+
+    # Returns +true+ if #flatten_with_monad can call recursively on contained
+    # values members (eg. elements of an array).
+    #
+    # NOTE: Is overridden in Hash.
+    def can_flatten_in_monad?
+      true
     end
   end
 end