Allow frozen_object.pry

lib/pry.rb

@@ -182,6 +182,15 @@ class Pry
     end
   end
 
+  # When we try to get a binding for an object, we try to define a method on
+  # that Object's singleton class. This doesn't work for "frozen" Object's, and
+  # the exception is just a vanilla RuntimeError.
+  module FrozenObjectException
+    def self.===(exception)
+      exception.message == (Pry::Helpers::BaseHelpers.jruby? ? "can't modify frozen class/module" : "can't modify frozen Class")
+    end
+  end
+
   # Don't catch these exceptions
   DEFAULT_EXCEPTION_WHITELIST = [SystemExit, SignalException, Pry::TooSafeException]
 

lib/pry/core_extensions.rb

@@ -89,7 +89,7 @@ class Object
       # If we can't define methods on the Object's singleton_class. Then we fall
       # back to setting the default definee to be the Object's class. That seems
       # nicer than having a REPL in which you can't define methods.
-      rescue TypeError
+      rescue TypeError, Pry::FrozenObjectException
         # class_eval sets the default definee to self.class
         self.class.class_eval(*Pry::BINDING_METHOD_IMPL)
       end

spec/pry_spec.rb

@@ -64,6 +64,11 @@ describe Pry do
         Pry.binding_for(obj).eval("local_variables").should.be.empty
       end
     end
+
+    it "should work on frozen objects" do
+      a = "hello".freeze
+      Pry.binding_for(a).eval("self").should.equal? a
+    end
   end
 
   describe "open a Pry session on an object" do