codegen: fix interpreter re-entrance

So multiple successive incremental Evals function correctly.

Also improve the following:
- Apply the same Eval API to vm0 and vm1
- parser: dot diagram display is now synchronous
- codegen: outsource complex code generation for readability
- vm1: Pop take the number of values to pop as operand

1 files changed, 5 insertions, 2 deletions

diff --git a/parser/dot.go b/parser/dot.go
index aae5c5f..f486cd5 100644
--- a/parser/dot.go
+++ b/parser/dot.go
@@ -20,8 +20,11 @@ func (*Parser) Adot(nodes []*Node, c string) {
 func (n *Node) Dot(c, s string) {
 	dw, cmd := dotWriter(c)
 	n.astDot(dw, s)
-	if cmd != nil {
-		cmd.Wait()
+	if cmd == nil {
+		return
+	}
+	if err := cmd.Wait(); err != nil {
+		log.Fatal(err)
 	}
 }