Sexplib library contains functionality for parsing and pretty-printing s-expressions.

sexplib also contains a preprocessing module for camlp4, which can be used to automatically generate code from type definitions for efficiently converting ocaml-values to s-expressions and vice versa. in combination with the parsing and pretty-printing functionality this frees users from having to write their own i/o-routines for the datastructures they define. possible errors during automatic conversions from s-expressions to ocaml-values are reported in a very human-readable way.

another module contained in sexplib you to extract and replace sub-expressions in s-expressions.