first working implementation of iterators and some fixes to the parser around lists analysis

operator-iter-value.go

@@ -0,0 +1,38 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-iter-value.go
+package expr
+
+
+//-------- iter value term
+
+func newIterValueTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 1),
+		position: posPrefix,
+		priority: priIterValue,
+		evalFunc: evalIterValue,
+	}
+}
+
+func evalIterValue(ctx ExprContext, self *term) (v any, err error) {
+	var leftValue any
+
+	if leftValue, err = self.evalPrefix(ctx); err != nil {
+		return
+	}
+
+	if dc, ok := leftValue.(*dataCursor); ok {
+		v, err = dc.Current()
+	} else {
+		err = self.errIncompatibleType(leftValue)
+	}
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymOpenClosedRound, newIterValueTerm)
+}