+ Improve RSpec matcher.

RSpec matcher :as chain now accepts a block. This allows for partial
assertions on the output, rather than just equality.

Also: try :trace => true in parse for error traces output.

lib/parslet/rig/rspec.rb

@@ -1,29 +1,43 @@
 RSpec::Matchers.define(:parse) do |input, opts|
-  chain(:as) { |as| @as = as }
-
   match do |parser|
     begin
       @result = parser.parse(input)
-      @as == @result or @as.nil?
+      @block ? @block.call(@result)
+             : (@as == @result || @as.nil?)
     rescue Parslet::ParseFailed
       @trace = parser.error_tree.ascii_tree if opts && opts[:trace]
       false
     end
   end
 
   failure_message_for_should do |is|
-    "expected " << 
-      (@as ?
-        "output of parsing #{input.inspect} with #{is.inspect} to equal #{@as.inspect}, but was #{@result.inspect}" :
-        "#{is.inspect} to be able to parse #{input.inspect}") << 
-      (@trace ? 
-        "\n"+@trace : '')
+    if @block
+      "expected output of parsing #{input.inspect}" <<
+      " with #{is.inspect} to meet block conditions, but it didn't"
+    else
+      "expected " << 
+        (@as  ? "output of parsing #{input.inspect}"<<
+                " with #{is.inspect} to equal #{@as.inspect}, but was #{@result.inspect}" 
+              : "#{is.inspect} to be able to parse #{input.inspect}") << 
+        (@trace ? "\n"+@trace 
+                : '')
+    end
   end
 
   failure_message_for_should_not do |is|
-    "expected " << 
-      (@as ?
-        "output of parsing #{input.inspect} with #{is.inspect} not to equal #{@as.inspect}" :
-        "#{is.inspect} to not parse #{input.inspect}, but it did")
+    if @block
+      "expected output of parsing #{input.inspect} with #{is.inspect} not to meet block conditions, but it did"
+    else
+      "expected " << 
+        (@as  ? "output of parsing #{input.inspect}"<<
+                " with #{is.inspect} not to equal #{@as.inspect}" 
+              : "#{is.inspect} to not parse #{input.inspect}, but it did")
+    end
+  end
+
+  def as(expected_output = nil, &block)
+    @as = expected_output
+    @block = block
+    self
   end
 end

spec/parslet/rig/rspec_spec.rb

@@ -14,13 +14,22 @@
   it { str('foo').as(:bar).should parse('foo').as({:bar => 'foo'}) }
   it { str('foo').as(:bar).should_not parse('foo').as({:b => 'f'}) }
 
+  it 'accepts a block to assert more specific details about the parsing output' do
+    str('foo').as(:bar).should(parse('foo').as { |output|
+      output.should have_key(:bar)
+      output.values.first.should == 'foo'
+    })
+  end
+
   # Uncomment to test error messages manually: 
   # it { str('foo').should parse('foo', :trace => true).as('bar') }
   # it { str('foo').should parse('food', :trace => true) }
   # it { str('foo').should_not parse('foo', :trace => true).as('foo') }
   # it { str('foo').should_not parse('foo', :trace => true) }
-  # it { str('foo').should parse('foo').as('bar') }
-  # it { str('foo').should parse('food') }
-  # it { str('foo').should_not parse('foo').as('foo') }
-  # it { str('foo').should_not parse('foo') }
+  # it 'accepts a block to assert more specific details about the parsing output' do
+  #   str('foo').as(:bar).should(parse('foo', :trace => true).as { |output|
+  #     output.should_not have_key(:bar)
+  #   })
+  # end
+
 end