array and linked-list: at operator

operator-at.go

@@ -0,0 +1,56 @@
+// Copyright (c) 2024-2026 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-at.go
+package expr
+
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+	"git.portale-stac.it/go-pkg/expr/scan"
+	"git.portale-stac.it/go-pkg/expr/types/array"
+	"git.portale-stac.it/go-pkg/expr/types/list"
+)
+
+//-------- at term
+
+func newAtTerm(tk *scan.Token) (inst *scan.Term) {
+	return &scan.Term{
+		Tk:       *tk,
+		Children: make([]*scan.Term, 0, 2),
+		Position: scan.PosInfix,
+		Priority: scan.PriRelational,
+		EvalFunc: evalAt,
+	}
+}
+
+// func hasKey(d map[any]any, target any) (ok bool) {
+// 	_, ok = d[target]
+// 	return
+// }
+
+func evalAt(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = opTerm.EvalInfix(ctx); err != nil {
+		return
+	}
+
+	if array.IsArray(rightValue) {
+		a, _ := rightValue.(*array.ArrayType)
+		v = a.IndexDeepSameCmp(leftValue)
+		// } else if dict.IsDict(rightValue) {
+		// 	dict, _ := rightValue.(*dict.DictType)
+		// 	v = dict.HasKey(leftValue)
+	} else if list.IsLinkedList(rightValue) {
+		ls, _ := rightValue.(*list.LinkedList)
+		v = ls.Index(leftValue)
+	} else {
+		err = opTerm.ErrIncompatibleTypes(leftValue, rightValue)
+	}
+	return
+}
+
+// init
+func init() {
+	scan.RegisterTermConstructor(scan.SymKwAt, newAtTerm)
+}