feat: add support for range clause and iterators

- vm: added Pull, Next and Stop instructions, to implement iterators
- lang: add Range, Next and Stop tokens
- parser: handle range clause. Still naive and incomplete.
- comp: generate iterator instructions from range clause.

Work in progress. Only initial support for slices. Many more tests
and combinations needed, but the main pattern is there now.

1 files changed, 18 insertions, 9 deletions

diff --git a/parser/parse.go b/parser/parse.go
index 46b1724..67d8657 100644
--- a/parser/parse.go
+++ b/parser/parse.go
@@ -193,25 +193,33 @@ func (p *Parser) parseGoto(in Tokens) (out Tokens, err error) {
 
 func (p *Parser) parseFor(in Tokens) (out Tokens, err error) {
 	// TODO: detect invalid code.
+	var init, cond, post, body, final Tokens
 	fc := strconv.Itoa(p.labelCount[p.scope])
 	p.labelCount[p.scope]++
-	var init, cond, post, body Tokens
+	breakLabel, continueLabel := p.breakLabel, p.continueLabel
+	p.pushScope("for" + fc)
+	p.breakLabel, p.continueLabel = p.scope+"e", p.scope+"b"
+	defer func() {
+		p.breakLabel, p.continueLabel = breakLabel, continueLabel
+		p.popScope()
+	}()
 	pre := in[1 : len(in)-1].Split(lang.Semicolon)
 	switch len(pre) {
 	case 1:
-		cond = pre[0]
+		if in.Index(lang.Range) >= 0 {
+			init = pre[0]
+			// cond = Tokens{{Tok: lang.Next, Str: p.scope + "c"}}
+			// final = Tokens{{Tok: lang.Stop, Str: p.scope + "f"}}
+			cond = Tokens{{Tok: lang.Next}}
+			final = Tokens{{Tok: lang.Stop}}
+		} else {
+			cond = pre[0]
+		}
 	case 3:
 		init, cond, post = pre[0], pre[1], pre[2]
 	default:
 		return nil, ErrFor
 	}
-	breakLabel, continueLabel := p.breakLabel, p.continueLabel
-	p.pushScope("for" + fc)
-	p.breakLabel, p.continueLabel = p.scope+"e", p.scope+"b"
-	defer func() {
-		p.breakLabel, p.continueLabel = breakLabel, continueLabel
-		p.popScope()
-	}()
 	if len(init) > 0 {
 		if init, err = p.parseStmt(init); err != nil {
 			return nil, err
@@ -239,6 +247,7 @@ func (p *Parser) parseFor(in Tokens) (out Tokens, err error) {
 	out = append(out,
 		scanner.Token{Tok: lang.Goto, Str: p.scope + "b"},
 		scanner.Token{Tok: lang.Label, Str: p.scope + "e"})
+	out = append(out, final...)
 	return out, err
 }