compile: 
File "toposort.ml", line 20, characters 6-7:
20 |     | _ -> 
           ^
Warning 11 [redundant-case]: this match case is unused.

File "_none_", line 1:
Alert ocaml_deprecated_auto_include: 
OCaml's lib directory layout changed in 5.0. The str subdirectory has been
automatically added to the search path, but you should add -I +str to the
command-line to silence this alert (e.g. by adding str to the list of
libraries in your dune file, or adding use_str to your _tags file for
ocamlbuild, or using -package str for ocamlfind).
finished

all tasks finished, build successfully