diff --git a/prototype/doubt-difftool/main.swift b/prototype/doubt-difftool/main.swift
index d473c045a..acb2e01e0 100644
--- a/prototype/doubt-difftool/main.swift
+++ b/prototype/doubt-difftool/main.swift
@@ -9,6 +9,29 @@ func readFile(path: String) -> String? {
 
 typealias Term = Cofree<String, Range<Int>>
 
+enum Category: String {
+	case Arguments = "arguments"
+	case Assignment = "assignment"
+	case Comment = "comment"
+	case ExpressionStatement = "expression_statement"
+	case FormalParameters = "formal_parameters"
+	case Function = "function"
+	case FunctionCall = "function_call"
+	case Identifier = "identifier"
+	case IfStatement = "if_statement"
+	case MemberAccess = "member_access"
+	case NewExpression = "new_expression"
+	case NullLiteral = "null"
+	case Object = "object"
+	case Pair = "pair"
+	case Program = "program"
+	case RelationalOperator = "rel_op"
+	case ReturnStatement = "return_statement"
+	case StatementBlock = "statement_block"
+	case StringLiteral = "string"
+	case SubscriptAccess = "subscript_access"
+}
+
 func termWithInput(string: String) -> Term? {
 	let document = ts_document_make()
 	defer { ts_document_free(document) }