interfaces

type Edge struct {
	Kind1 string // kind of resource
	Name1 string // name of resource
	Send  string // name of field used for send/recv (optional)

	Kind2 string // kind of resource
	Name2 string // name of resource
	Recv  string // name of field used for send/recv (optional)

	Notify bool // is there a notification being sent?
}

type Error string

type Expr interface {
	pgraph.Vertex               // must implement this since we store these in our graphs
	Interpolate() (Expr, error) // return expanded form of AST as a new AST
	SetScope(*Scope) error      // set the scope here and propagate it downwards
	SetType(*types.Type) error  // sets the type definitively, errors if incompatible
	Type() (*types.Type, error)
	Unify() ([]Invariant, error) // TODO: is this named correctly?
	Graph() (*pgraph.Graph, error)
	Func() (Func, error) // a function that represents this reactively
	SetValue(types.Value) error
	Value() (types.Value, error)
}

type Func interface {
	Validate() error // FIXME: this is only needed for PolyFunc. Get it moved and used!
	Info() *Info
	Init(*Init) error
	Stream() error
	Close() error
}

type Info struct {
	Pure bool        // is the function pure? (can it be memoized?)
	Memo bool        // should the function be memoized? (false if too much output)
	Sig  *types.Type // the signature of the function, must be KindFunc
	Err  error       // is this a valid function, or was it created improperly?
}

type Init struct {
	Hostname string // uuid for the host
	//Noop bool
	Input  chan types.Value // Engine will close `input` chan
	Output chan types.Value // Stream must close `output` chan
	World  resources.World
	Debug  bool
	Logf   func(format string, v ...interface{})
}

type Invariant interface {
	// TODO: should we add any other methods to this type?
	fmt.Stringer
}

type Output struct {
	Resources []resources.Res
	Edges     []*Edge
}

type PolyFunc interface {
	Func // implement everything in Func but add the additional requirements

	// Polymorphisms returns a list of possible function type signatures. It
	// takes as input a list of partial "hints" as to limit the number of
	// possible results it returns. These partial hints take the form of a
	// function type signature (with as many types in it specified and the
	// rest set to nil) and any known static values for the input args. If
	// the partial type is not nil, then the Ord parameter must be of the
	// correct arg length. If any types are specified, then the array must
	// be of that length as well, with the known ones filled in. Some
	// static polymorphic functions require a minimal amount of hinting or
	// they will be unable to return any possible result that is not
	// infinite in length. If you expect to need to return an infinite (or
	// very large) amount of results, then you should return an error
	// instead. The arg names in your returned func type signatures should
	// be in the standardized "a..b..c" format. Use util.NumToAlpha if you
	// want to convert easily.
	Polymorphisms(*types.Type, []types.Value) ([]*types.Type, error)

	// Build takes the known type signature for this function and finalizes
	// this structure so that it is now determined, and ready to function as
	// a normal function would. (The normal methods in the Func interface
	// are all that should be needed or used after this point.)
	Build(*types.Type) error // then, you can get argNames from Info()
}

type Scope struct {
	Variables map[string]Expr
}

type Stmt interface {
	Interpolate() (Stmt, error)  // return expanded form of AST as a new AST
	SetScope(*Scope) error       // set the scope here and propagate it downwards
	Unify() ([]Invariant, error) // TODO: is this named correctly?
	Graph() (*pgraph.Graph, error)
	Output() (*Output, error)
}