gistfile1.txt

import Stencil

let text = "{% exact %} {{aaa}} {% endexact %}"

let ext = Extension()

class ExactNode: NodeType {
    
    let string: String
    init(_ string: String) {
        self.string = string
    }
    func render(_ context:Context) throws -> String {
        return self.string
    }
    
    class func parse(_ parser: TokenParser) -> ExactNode {
        var string = ""
        loop: while let token = parser.nextToken() {
            switch token {
            case .block(value: "endexact"):
                break loop
            case .block(value: let value):
                string += "{%" + value + "%}"
            case .text(value: let value):
                string += value
            case .variable(value: let value):
                string += "{{" + value + "}}"
            default:
                break
            }
        }
            
        return ExactNode(string)
    }
}
ext.registerTag("exact") { parser, token in
    print(token)
    return ExactNode.parse(parser)
}

let e = Environment(extensions: [ext])
print(try e.renderTemplate(string: text, context: ["aaa" : 10]))