New operators 'but' and assignment ('=')

operator-but.go

@@ -0,0 +1,29 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-but.go
+package expr
+
+//-------- but term
+
+func newButTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		class:    classOperator,
+		kind:     kindUnknown,
+		children: make([]*term, 0, 2),
+		position: posInfix,
+		priority: priBut,
+		evalFunc: evalBut,
+	}
+}
+
+func evalBut(ctx exprContext, self *term) (v any, err error) {
+	_, v, err = self.evalInfix(ctx)
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymKwBut, newButTerm)
+}