Attaching Debugger Views

The new functionality in parsley-debug involves attaching a debugger to a parser that will be ran. There are two combinators to do this found in parsley.debug.combinator: attach, and attachReusable. Before we see these, it will be useful to understand how DebugViews work.

DebugView

The DebugView.SingleUse and DebugView.Reusable traits represent renderers for debug information. By default, parsley-debug includes PrintView, which can be used to "render" debug information out onto the console, or perhaps to a file (or any PrintStream/OutputStream). The reusability aspect refers to whether or not multiple such views can work simultaneously: see attachReusable below.

The views themselves do not necessarily have to directly render the debugging content themselves, they could be remote connections, for instance; but the point is that they are what is attached to a specific parser. When the parser is ran, the debug combinator collects the information, and the view processes that information in some way. This process is done via attachment.

attach and attachReusable

The attach combinator takes a DebugView (reusable or otherwise) and optionally a "string rules" function, which determines whether or not a value is eagerly turned into a string or preserved in its original form within the internal "DebugTree". In return, you get a new parser, which will feed debugging information to the provided DebugView.

In contrast, attachReusable is similar, but takes a by-name DebugView, which may be recreated each use, and returns a function that produces new Parsley values. The idea is that if you need to use the parser in more than one place, you call the function more than once to produce independently bound parsers.