From 353d495c50ccb326c37f80ad8c5da77d7f0c0a80 Mon Sep 17 00:00:00 2001
From: Celestino Amoroso <celestino.amoroso@gmail.com>
Date: Tue, 16 Apr 2024 03:54:50 +0200
Subject: [PATCH] two new operators added: '<<' and '>>

---
 operator-insert.go | 66 ++++++++++++++++++++++++++++++++++++++++++++++
 operator-sum.go    |  4 +--
 scanner.go         |  4 +++
 symbol.go          |  2 ++
 4 files changed, 73 insertions(+), 3 deletions(-)
 create mode 100644 operator-insert.go

diff --git a/operator-insert.go b/operator-insert.go
new file mode 100644
index 0000000..3a71c64
--- /dev/null
+++ b/operator-insert.go
@@ -0,0 +1,66 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-insert.go
+package expr
+
+
+//-------- insert term
+
+func newInsertTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 2),
+		position: posInfix,
+		priority: priSign,
+		evalFunc: evalInsert,
+	}
+}
+
+func newAppendTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 2),
+		position: posInfix,
+		priority: priSign,
+		evalFunc: evalAppend,
+	}
+}
+
+func evalInsert(ctx ExprContext, self *term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+		return
+	}
+
+	if isList(rightValue) {
+		list, _ := rightValue.([]any)
+		v = append([]any{leftValue}, list...)
+	} else {
+		err = self.errIncompatibleType(rightValue)
+	}
+	return
+}
+
+func evalAppend(ctx ExprContext, self *term) (v any, err error) {
+	var leftValue, rightValue any
+
+	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
+		return
+	}
+
+	if isList(leftValue) {
+		list, _ := leftValue.([]any)
+		v = append(list, rightValue)
+	} else {
+		err = self.errIncompatibleType(leftValue)
+	}
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymInsert, newInsertTerm)
+	registerTermConstructor(SymAppend, newAppendTerm)
+}
diff --git a/operator-sum.go b/operator-sum.go
index ac0f21b..53cd520 100644
--- a/operator-sum.go
+++ b/operator-sum.go
@@ -65,9 +65,7 @@ func evalPlus(ctx ExprContext, self *term) (v any, err error) {
 
 func newMinusTerm(tk *Token) (inst *term) {
 	return &term{
-		tk: *tk,
-		// class:    classOperator,
-		// kind:     kindUnknown,
+		tk:       *tk,
 		children: make([]*term, 0, 2),
 		position: posInfix,
 		priority: priSum,
diff --git a/scanner.go b/scanner.go
index f244f29..e4eb848 100644
--- a/scanner.go
+++ b/scanner.go
@@ -219,6 +219,8 @@ func (self *scanner) fetchNextToken() (tk *Token) {
 		case '<':
 			if next, _ := self.peek(); next == '=' {
 				tk = self.moveOn(SymLessOrEqual, ch, next)
+			} else if next == '<' {
+				tk = self.moveOn(SymAppend, ch, next)
 			} else if next == '>' {
 				tk = self.moveOn(SymLessGreater, ch, next)
 			} else {
@@ -227,6 +229,8 @@ func (self *scanner) fetchNextToken() (tk *Token) {
 		case '>':
 			if next, _ := self.peek(); next == '=' {
 				tk = self.moveOn(SymGreaterOrEqual, ch, next)
+			} else if next == '>' {
+				tk = self.moveOn(SymInsert, ch, next)
 			} else {
 				tk = self.makeToken(SymGreater, ch)
 			}
diff --git a/symbol.go b/symbol.go
index 5ebe214..341fc78 100644
--- a/symbol.go
+++ b/symbol.go
@@ -59,6 +59,8 @@ const (
 	SymQuestionEqual                     //  48: '?='
 	SymDoubleAt                          //  49: '@@'
 	SymDoubleColon                       //  50: '::'
+	SymInsert                            //  51: '>>'
+	SymAppend                            //  52: '<<'
 	SymChangeSign
 	SymUnchangeSign
 	SymIdentifier