The config-ini Haskell library exports some simple monadic functions to ease the parsing of .ini-style configuration files, and to write and update them in an efficient diff-minimal way. This means that if you parse a file, update a single field, and reserialize, that file should differ only in the field we changed and that's it: field order, comments, and incidental whitespace will remain unchanged. The library aims to produce human-readable error messages when things go wrong.