hi wren Where I've used it, random access does seem conceptual more satisfactory than trying to avoid it. Well designed binary formats are deterministic - so wherever you are inside the file you should know what you are parsing. One example of this determinism is that parsing "local" alternatives are generally encoded on a single tag, whereas in a parser for a programming language parsing alternatives might require lookahead and possibly other disambiguation. Another example is that formats will often have a "index table" table at the start of the file giving start position and length for all the sub tables - this saves you from having to start each table with a tag and length. For complex formats e.g. PECOFF or TrueType, you might only want to parse certain tables [*]. After parsing the index table you could build a list of parsers to run sequentially on the body of the file (including parsers that just drop unwanted tables), but this seems too much work (and too much to go wrong), when I can use a function almost as simple as parseAt for the tables I'm interested in. parseAt :: Start -> End -> Parser a -> Parser a In practice, I made parseAt slightly more complicated so it could encode where the cursor is moved to at the end of the parse. Best wishes Stephen [*] Certain tables in TrueType / OpenType are propriety - it might be unwise for an open source parser to even include parsing operations for those tables.