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, 15 insertions, 9 deletions

diff --git a/codegen/interpreter.go b/codegen/interpreter.go
index b26b403..a3268d9 100644
--- a/codegen/interpreter.go
+++ b/codegen/interpreter.go
@@ -19,24 +19,30 @@ func NewInterpreter(p *parser.Parser) *Interpreter {
 	return &Interpreter{p, NewCompiler(), &vm1.Machine{}}
 }
 
-func (i *Interpreter) Eval(src string) (err error) {
+func (i *Interpreter) Eval(src string) (res any, err error) {
 	n := &parser.Node{}
 	if n.Child, err = i.Parse(src); err != nil {
-		return err
+		return res, err
 	}
 	if debug {
 		n.Dot(os.Getenv("DOT"), "")
 	}
-	offset := len(i.Code)
-	i.PopExit() // Remove last exit from previous run.
+	codeOffset := len(i.Code)
+	dataOffset := 0
+	if codeOffset > 0 {
+		// All data must be copied to the VM the first time only (re-entrance).
+		dataOffset = len(i.Data)
+	}
+	i.PopExit() // Remove last exit from previous run (re-entrance).
 	if err = i.CodeGen(n); err != nil {
-		return err
+		return res, err
 	}
-	i.Push(i.Data...)
-	i.PushCode(i.Code[offset:]...)
+	i.Push(i.Data[dataOffset:]...)
+	i.PushCode(i.Code[codeOffset:]...)
 	i.PushCode([]int64{0, vm1.Exit})
-	i.SetIP(max(offset, i.Entry))
-	return i.Run()
+	i.SetIP(max(codeOffset, i.Entry))
+	err = i.Run()
+	return i.Top(), err
 }
 
 func max(a, b int) int {