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, 15 insertions, 0 deletions

diff --git a/parser/interpreter_test.go b/parser/interpreter_test.go
index 3a5598e..7ac1212 100644
--- a/parser/interpreter_test.go
+++ b/parser/interpreter_test.go
@@ -164,6 +164,21 @@ func TestSwitch(t *testing.T) {
 	})
 }
 
+func TestConst(t *testing.T) {
+	src0 := `const (
+	a = iota
+	b
+	c
+)
+`
+	run(t, []etest{
+		{src: "const a = 1+2; a", res: "3"},
+		{src: "const a, b = 1, 2; a+b", res: "3"},
+
+		{src: src0 + "c", res: "2"},
+	})
+}
+
 func TestType(t *testing.T) {
 	run(t, []etest{
 		{src: "type t int; var a t = 1; a", res: "1"},