lang: Improve graph shape with speculative execution

Most of the time, we don't need to have a dynamic call sub graph, since
the actual function call could be represented statically as it
originally was before lambda functions were implemented. Simplifying the
graph shape has important performance benefits in terms of both keep the
graph smaller (memory, etc) and in avoiding the need to run transactions
at runtime (speed) to reshape the graph.

Co-authored-by: Samuel Gélineau <gelisam@gmail.com>

lang/core/world/kvlookup.go

@@ -93,6 +93,8 @@ func (obj *KVLookupFunc) Info() *interfaces.Info {
 	return &interfaces.Info{
 		Pure: false, // definitely false
 		Memo: false,
+		Fast: false,
+		Spec: false,
 		// output is map of: hostname => value
 		Sig: types.NewType(fmt.Sprintf("func(%s str) map{str: str}", kvLookupArgNameNamespace)),
 		Err: obj.Validate(),
@@ -211,7 +213,13 @@ func (obj *KVLookupFunc) Stream(ctx context.Context) error {
 // to do so at this time. This was previously buildMap, which builds the result
 // map which we'll need. It uses struct variables.
 func (obj *KVLookupFunc) Call(ctx context.Context, args []types.Value) (types.Value, error) {
+	if len(args) < 1 {
+		return nil, fmt.Errorf("not enough args")
+	}
 	namespace := args[0].Str()
+	if obj.init == nil {
+		return nil, funcs.ErrCantSpeculate
+	}
 	keyMap, err := obj.init.World.StrMapGet(ctx, namespace)
 	if err != nil {
 		return nil, errwrap.Wrapf(err, "channel read failed on `%s`", namespace)