Add pretty_print methods to Result and Maybe

lib/dry/monads/maybe.rb

@@ -169,6 +169,17 @@ def to_s
           end
         end
         alias_method :inspect, :to_s
+
+        def pretty_print(pp)
+          pp.text "Some("
+          unless Unit.equal?(@value)
+            pp.group(1) do
+              pp.breakable("")
+              pp.pp(@value)
+            end
+          end
+          pp.text ")"
+        end
       end
 
       # Represents an absence of a value, i.e. the value nil.
@@ -238,6 +249,10 @@ def or_fmap(...) = Maybe.coerce(self.or(...))
         def to_s = "None"
         alias_method :inspect, :to_s
 
+        def pretty_print(pp)
+          pp.text "None"
+        end
+
         # @api private
         def eql?(other) = other.is_a?(None)
 

lib/dry/monads/result.rb

@@ -116,6 +116,17 @@ def to_s
         end
         alias_method :inspect, :to_s
 
+        def pretty_print(pp)
+          pp.text "Success("
+          unless Unit.equal?(@value)
+            pp.group(1) do
+              pp.breakable("")
+              pp.pp(@value)
+            end
+          end
+          pp.text ")"
+        end
+
         # Transforms to a Failure instance
         #
         # @return [Result::Failure]
@@ -227,6 +238,17 @@ def to_s
         end
         alias_method :inspect, :to_s
 
+        def pretty_print(pp)
+          pp.text "Failure("
+          unless Unit.equal?(@value)
+            pp.group(1) do
+              pp.breakable("")
+              pp.pp(@value)
+            end
+          end
+          pp.text ")"
+        end
+
         # Transform to a Success instance
         #
         # @return [Result::Success]

spec/unit/maybe_spec.rb

@@ -52,6 +52,16 @@
       expect(subject.inspect).to eql('Some("foo")')
     end
 
+    it "pretty prints" do
+      out = +""
+      PP.pp(subject, out)
+      expect(out).to eql(%{Some("foo")\n})
+
+      out = +""
+      PP.pp(some[unit], out)
+      expect(out).to eql("Some()\n")
+    end
+
     describe ".to_proc" do
       it "returns a constructor block" do
         expect(maybe::Some.to_proc.("foo")).to eql(subject)
@@ -305,6 +315,12 @@
       expect(subject.inspect).to eql("None")
     end
 
+    it "pretty prints" do
+      out = +""
+      PP.pp(subject, out)
+      expect(out).to eql(%(None\n))
+    end
+
     describe ".missing_method" do
       it "shows a friendly error messsage if an instance method is called" do
         expect { described_class.fmap }.to raise_error(

spec/unit/result_spec.rb

@@ -40,6 +40,16 @@
       expect(subject.inspect).to eql('Success("foo")')
     end
 
+    it "pretty prints" do
+      out = +""
+      PP.pp(subject, out)
+      expect(out).to eql(%{Success("foo")\n})
+
+      out = +""
+      PP.pp(success[unit], out)
+      expect(out).to eql("Success()\n")
+    end
+
     describe ".[]" do
       it "builds a Success with an array" do
         expect(described_class[:found, 1]).to eql(success[[:found, 1]])
@@ -351,6 +361,16 @@
       expect(subject.inspect).to eql('Failure("bar")')
     end
 
+    it "pretty prints" do
+      out = +""
+      PP.pp(subject, out)
+      expect(out).to eql(%{Failure("bar")\n})
+
+      out = +""
+      PP.pp(failure[unit], out)
+      expect(out).to eql("Failure()\n")
+    end
+
     describe ".[]" do
       it "builds a Failure with an array" do
         expect(described_class[:not_found, :but_tried]).to eql(failure[[:not_found, :but_tried]])