Let's try MonadThrow/MonadCatch. It looks nice at a first glance. The
monad transformer stack contains only the ReaderT, less lifts are
required. Exception subtyping is easier, the user can (and should)
define custom error types and throw them. And it is still possible to
use pure error handling, if someone doesn't like runtime exceptions or
need to run a query in a pure environment.
Fixes#42.
After the last commit there were a few places needed to be adjusted to
support subscriptions. This is done and a test case is added.
It is important to implement subscriptions now, because they require
changes to the library API, and they are a big missing part to finish
the executor. When the executor is finished, we can start to provide
more stable API without breaking everything every release. Validation
and introspection shouldn't require much changes to the API; AST would
require some changes to report good errors after the validation - this
is one thing I can think of.
Fixes#5.
This is experimental support.
The implementation is based on conduit and is boring. There is a new
resolver data constructor that should create a source event stream. The
executor receives the events, pipes them through the normal execution
and puts them into the response stream which is returned to the user.
- Tests are missing.
- The executor should check field value resolver on subscription types.
- The graphql function should probably return (Either
ResponseEventStream Response), but I'm not sure about this. It will
make the usage more complicated if no subscriptions are involved, but
with the current API implementing subscriptions is more
difficult than it should be.
Returning resolvers from other resolvers isn't supported anymore. Since
we have a type system now, we define the resolvers in the object type
fields and pass an object with the previous result to them.
It makes using variables with queries more approachable, but some work
still has to be done.
- The type `Subs` should be renamed and moved out of `Schema`, together with
`AST.Core.Value` probably.
- Some kind of conversion should be possible from a user-defined input
type T to the Value. So the final HashMap should have a type like
`HashMap name a`, where a is an instance of a potential typeclass
InputType.
Language.GraphQL.AST.Transform is an internal module. Even though it
works with the AST, it is a part of the execution process, it translates
the original parser tree into a simpler one, so the executor has less
work to do. Language.GraphQL.AST should contain only the parser and be
independent from other packages, so it can be used on its own.
