From b6887af77ad7267eb884ed72f2c1b5c053f6f85e Mon Sep 17 00:00:00 2001
From: Celestino Amoroso <celestino.amoroso@gmail.com>
Date: Wed, 17 Apr 2024 07:12:32 +0200
Subject: [PATCH] added the prefix operator '#' (length of string and array)

---
 operator-length.go | 44 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)
 create mode 100644 operator-length.go

diff --git a/operator-length.go b/operator-length.go
new file mode 100644
index 0000000..5d895e7
--- /dev/null
+++ b/operator-length.go
@@ -0,0 +1,44 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-length.go
+package expr
+
+//-------- length term
+
+func newLengthTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 1),
+		position: posPrefix,
+		priority: priSign,
+		evalFunc: evalLength,
+	}
+}
+
+func evalLength(ctx ExprContext, self *term) (v any, err error) {
+	var rightValue any
+
+	if rightValue, err = self.evalPrefix(ctx); err != nil {
+		return
+	}
+
+	if isList(rightValue) {
+		list, _ := rightValue.([]any)
+		v = len(list)
+	} else if isString(rightValue) {
+		s, _ := rightValue.(string)
+		v = len(s)
+		// } else {
+		// 	v = 1
+		// }
+	} else {
+		err = self.errIncompatibleType(rightValue)
+	}
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymHash, newLengthTerm)
+}