New operator unset to delete variables and functions from current context

operator-unset.go

@@ -0,0 +1,69 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-unset.go
+package expr
+
+import "strings"
+
+//-------- unset term
+
+func newUnsetTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 1),
+		position: posPrefix,
+		priority: priSign,
+		evalFunc: evalUnset,
+	}
+}
+
+func deleteContextItem(ctx ExprContext, opTerm *term, item any) (deleted bool, err error) {
+	if name, ok := item.(string); ok {
+		var size int
+		if strings.HasSuffix(name, "()") {
+			size = ctx.FuncCount()
+			ctx.DeleteVar(strings.TrimRight(name, "()"))
+			deleted = ctx.FuncCount() < size
+		} else {
+			size = ctx.VarCount()
+			ctx.DeleteVar(name)
+			deleted = ctx.VarCount() < size
+		}
+	} else {
+		err = opTerm.errIncompatibleType(item)
+	}
+	return
+}
+
+func evalUnset(ctx ExprContext, opTerm *term) (v any, err error) {
+	var childValue any
+	var deleted bool
+
+	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
+		return
+	}
+
+	count := 0
+	if IsList(childValue) {
+		list, _ := childValue.(*ListType)
+		for _, item := range *list {
+			if deleted, err = deleteContextItem(ctx, opTerm, item); err != nil {
+				break
+			} else if deleted {
+				count++
+			}
+		}
+	} else if deleted, err = deleteContextItem(ctx, opTerm, childValue); err == nil && deleted {
+		count++
+	}
+	if err == nil {
+		v = int64(count)
+	}
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymKwUnset, newUnsetTerm)
+}

symbol.go

@@ -106,6 +106,7 @@ const (
 	SymKwIn
 	SymKwInclude
 	SymKwNil
+	SymKwUnset
 )
 
 var keywords map[string]Symbol
@@ -123,5 +124,6 @@ func init() {
 		"NOT":     SymKwNot,
 		"OR":      SymKwOr,
 		"NIL":     SymKwNil,
+		"UNSET":   SymKwUnset,
 	}
 }

t_operator_test.go

@@ -0,0 +1,22 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// t_operator_test.go
+package expr
+
+import (
+	"testing"
+)
+
+func TestOperator(t *testing.T) {
+	section := "Operator"
+	inputs := []inputType{
+		/*   1 */ {`a=1; unset "a"; a`, nil, `undefined variable or function "a"`},
+		/*   2 */ {`a=1; unset ["a", "b"]`, int64(1), nil},
+	}
+
+	// t.Setenv("EXPR_PATH", ".")
+
+	runTestSuiteSpec(t, section, inputs, 2)
+	//runTestSuite(t, section, inputs)
+}