[Haskell-cafe] Parsec without data declarations/AST

I have been trying to create a parser for a functional programming language, but there is no need to create an AST but merely check that the code is valid according to the grammar. In the following tutorial I have been trying to take some pointers from, data declarations are used to create an AST for the language, There is, as I understand a way to parse the language without an AST. http://www.haskell.org/haskellwiki/Parsing_a_simple_imperative_language My question is what should the type signatures for example parseFile function instead of "Stmt" accept as input if the parser is to accept Strings and numerical expressions alike ? Thanks for any help, Seán