parser: hande const declarations

Only symbols are produced, no bytecode is emitted. The constant
expressions are evaluated at compile time using the stdlib package
go/constant. The parser handles implicit repetition of the last
non-empty expression list. The iota symbol is reset to 0 and
incremented for each line of a const block.

To be done in a next commit: type conversions.

1 files changed, 6 insertions, 4 deletions

diff --git a/vm/vm.go b/vm/vm.go
index ba1f97e..f7f4d78 100644
--- a/vm/vm.go
+++ b/vm/vm.go
@@ -71,12 +71,14 @@ var strop = [...]string{ // for VM tracing.
 	Subi:         "Subi",
 }
 
+type Code [][]int64
+
 // Machine represents a virtual machine.
 type Machine struct {
-	code   [][]int64 // code to execute
-	mem    []any     // memory, as a stack
-	ip, fp int       // instruction and frame pointer
-	ic     uint64    // instruction counter, incremented at each instruction executed
+	code   Code   // code to execute
+	mem    []any  // memory, as a stack
+	ip, fp int    // instruction and frame pointer
+	ic     uint64 // instruction counter, incremented at each instruction executed
 	// flags  uint      // to set options such as restrict CallX, etc...
 }