[mafribe]

Parser combinators tend to work by recursive descent, so cannot handle left recursive grammars [1], and tend to be really slow. The latter is not a problem for many applications, but removing left recursion can be irritating even for small grammars. It is possible to build combinator parsers that can handle all context-free grammars [2], but I'm not sure any of Ocaml's are built that way.

In any case, Ocaml has parser generators that are fast, do bottom-up parsing (hence handle left-recursion without issue) and not based on parser combinators, e.g. ocamlyacc [3].

I'd use parser combinators for quick prototypes, and, if measurement shows a performance problem, replace them with a generated (e.g. by ocamlyacc) parser. As far as I remember the parser in Ocaml's (superfast) compiler is generated by ocamlyacc.

[1] https://en.wikipedia.org/wiki/Left_recursion

[2] T. Ridge, Simple, functional, sound and complete parsing for all context-free grammars. http://www.tom-ridge.com/resources/ridge11parsing-cpp.pdf

[3] https://caml.inria.fr/pub/docs/manual-ocaml/lexyacc.html