Allow passing of concatFn

src/parser/builder_api.nim

@@ -15,6 +15,7 @@ proc tryParseBuild*[T](
   ]],
   defaultBuilderFn: seq[ParserToken] -> seq[T],
   stopAtParserFn = newline,
+  concatFn = concat[T],
 ): BuilderResult[T] =
   ## Parse remaining text in `builder` by going checking in the `builderFns` list for a sucessful `parserFn`.
   ## The `ok` `parserFn` result will be merged into the `Builder[T].tree` by using the `concatFn`.
@@ -50,7 +51,7 @@ proc tryParseBuild*[T](
         parserAcc = parseResult.map(emptyTokens)
         builderAcc = builder.initBuilder(
           okParser,
-          concat(
+          concatFn(
             builderAcc.tree,
             defaultBuilderTokens,
             builderFn(okParser.tokens),
@@ -69,7 +70,7 @@ proc tryParseBuild*[T](
 
   BuilderResult[T].ok(builder.initBuilder(
     builderAcc.parser,
-    concat(
+    concatFn(
       builderAcc.tree,
       defaultBuilderTokens,
     ),