The compiler library chose to keep it's implementation simple and clean, at the cost of not being tail-recursive, and therefore unsuitable for large lists. This is documented in the manual:
http://caml.inria.fr/pub/docs/manual-ocaml/libref/List.html>
Some functions are flagged as not tail-recursive. A tail-recursive
function uses constant stack space, while a non-tail-recursive function
uses stack space proportional to the length of its list argument, which
can be a problem with very long lists.
>
List.map f [a1; ...; an] applies function
f to
a1, ..., an,
and builds the list
[f a1; ...; f an]
with the results returned by
f. Not tail-recursive.
Other libraries have made different design choices, so you can easily use a different List module that provides tail-recursive operations. There are several larger libraries, some (such as Batteries
http://batteries.forge.ocamlcore.org/ ) which directly extend the compiler library, and are therefore usable as a drop-in replacement for it, some others (such as Core
https://ocaml.janestreet.com/ocaml-core/111.28.00/doc/core/ ) which use different conventions. They all provide tail-recursive mapping functions suitable for use on long lists.
(Of course you can also simply replace `List.map f li` with `List.rev_map f (List.rev li)` if you know `li` may be long.)