opam

• Add a version constraint to an opam install

Add a version constraint to an opam install

$ opam install utop
...
<><> Processing actions <><><><><><><><><><><><><><><><><><><><><><><><><><><><>
⬇ retrieved lambda-term.3.3.3  (cached)
⬇ retrieved logs.0.9.0  (cached)
⬇ retrieved lwt.6.1.0  (cached)
⬇ retrieved lwt_react.1.2.0  (cached)
⬇ retrieved utop.2.16.0+ox  (cached)
[ERROR] The compilation of lwt.6.1.0 failed at "dune build -p lwt -j 15 @install".

#=== ERROR while compiling lwt.6.1.0 ==========================================#

On an old OxCaml, the new lwt 6 doesn't build, and naturally lwt isn't as aware of this OCaml fork. But you can just add constraints:

$ opam install utop 'lwt<6'
The following actions will be performed:
=== install 5 packages
  ∗ lambda-term 3.3.3     [required by utop]
  ∗ logs        0.9.0     [required by utop]
  ∗ lwt         5.9.2+ox
  ∗ lwt_react   1.2.0     [required by utop]
  ∗ utop        2.16.0+ox

Proceed with ∗ 5 installations? [Y/n] y

<><> Processing actions <><><><><><><><><><><><><><><><><><><><><><><><><><><><>
⬇ retrieved lambda-term.3.3.3  (cached)
⬇ retrieved logs.0.9.0  (cached)
⬇ retrieved lwt.5.9.2+ox  (cached)
⬇ retrieved lwt_react.1.2.0  (cached)
⬇ retrieved utop.2.16.0+ox  (cached)
∗ installed lwt.5.9.2+ox
∗ installed lwt_react.1.2.0
∗ installed logs.0.9.0
∗ installed lambda-term.3.3.3
∗ installed utop.2.16.0+ox
Done.