reason 3.9.0

Error log

The package failed to build. The error log from opam follows.

[NOTE] Package dune is already installed (current version is 3.17.2).
[NOTE] Package ocamlfind is already installed (current version is 1.9.8).
[ERROR] Package conflict!
  * Incompatible packages:
    - (invariant) -> ocaml-base-compiler = 5.1.1
    - melange = 1.0.0 -> ocaml < 5.1.1 -> dkml-base-compiler
    You can temporarily relax the switch invariant with `--update-invariant'
  * Incompatible packages:
    - (invariant) -> ocaml-base-compiler = 5.1.1
    - melange = 1.0.0 -> ocaml < 5.1.1 -> ocaml-variants (< 4.00.1~ | >= 4.00.1)
  * Missing dependency:
    - melange = 1.0.0 -> ocaml < 5.1.1 -> ocaml-base-compiler (<= 3.07+1 | = 3.07+2 | = 3.08.0 | = 3.08.1 | = 3.08.2 | = 3.08.3 | = 3.08.4 | = 3.09.0) | ocaml-system (<= 3.07+1 | = 3.07+2 | >= 3.08.0) | ocaml-variants < 3.09.1~
    not available because the package is pinned to version 5.1.1
    unmet availability conditions, e.g. 'sys-ocaml-version = "5.3.0" & (os != "win32" | sys-ocaml-libc = "msvc")'
    no matching version
  * Missing dependency:
    - melange = 1.0.0 -> ocaml < 5.1.1 -> ocaml-variants >= 4.00.1 -> ocaml-beta
    unmet availability conditions: 'enable-ocaml-beta-repository'
  * Missing dependency:
    - melange = 1.0.0 -> ocaml < 5.1.1 -> ocaml-variants >= 4.00.1 -> system-msvc
    unmet availability conditions: 'os = "win32"'

No solution found, exiting