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/getval.go

@@ -97,6 +97,8 @@ func (obj *GetValFunc) Info() *interfaces.Info {
 	return &interfaces.Info{
 		Pure: false, // definitely false
 		Memo: false,
+		Fast: false,
+		Spec: false,
 		// output is a struct with two fields:
 		// value is the zero value if not exists. A bool for that in other field.
 		Sig: types.NewType(fmt.Sprintf("func(%s str) struct{%s str; %s bool}", getValArgNameKey, getValFieldNameValue, getValFieldNameExists)),
@@ -206,8 +208,14 @@ func (obj *GetValFunc) Stream(ctx context.Context) error {
 // to do so at this time. This was previously getValue which gets the value
 // we're looking for.
 func (obj *GetValFunc) Call(ctx context.Context, args []types.Value) (types.Value, error) {
+	if len(args) < 1 {
+		return nil, fmt.Errorf("not enough args")
+	}
 	key := args[0].Str()
 	exists := true // assume true
+	if obj.init == nil {
+		return nil, funcs.ErrCantSpeculate
+	}
 	val, err := obj.init.World.StrGet(ctx, key)
 	if err != nil && obj.init.World.StrIsNotExist(err) {
 		exists = false // val doesn't exist