merlin 3.3.4~4.10preview1

Error log

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

Opam plugin "depext" may require upgrading/reinstalling. Reinstall the plugin on the current switch? [Y/n] y
The following actions will be performed:
  - recompile opam-depext 1.2.1-1

<><> Processing actions <><><><><><><><><><><><><><><><><><><><><><><><><><><><>
-> retrieved opam-depext.1.2.1-1  (cached)
-> removed   opam-depext.1.2.1-1
-> installed opam-depext.1.2.1-1
Done.

<><> opam-depext.1.2.1-1 installed successfully <><><><><><><><><><><><><><><><>
=> opam-depext is unnecessary when used with opam >= 2.1. Please use opam install directly instead
# Run eval $(opam env) to update the current shell environment

<><> Carrying on to "opam depext -viy merlin.3.3.4~4.10preview1 yojson.1.7.0 ocamlfind.1.9.6 easy-format.1.3.2 dune.2.7.1 cppo.1.6.9 biniou.1.2.1" 

You are using opam 2.1+, where external dependency handling has been integrated: consider calling opam directly, the 'depext' plugin interface is provided for backwards compatibility only
# Detecting depexts using vars: arch=x86_64, os=linux, os-distribution=debian, os-family=debian
[ERROR] No solution for merlin.3.3.4~4.10preview1 & yojson.1.7.0 & ocamlfind.1.9.6 & easy-format.1.3.2 & dune.2.7.1 & cppo.1.6.9 & biniou.1.2.1:   * Incompatible packages:
            - (invariant) -> ocaml-base-compiler = 4.10.2
            - merlin = 3.3.4~4.10preview1 -> ocaml = 4.10.0 -> ocaml-system >= 4.10.0
            You can temporarily relax the switch invariant with `--update-invariant'
          * Missing dependency:
            - merlin = 3.3.4~4.10preview1 -> ocaml = 4.10.0 -> ocaml-variants >= 4.10.0 -> ocaml-beta
            unmet availability conditions: 'enable-ocaml-beta-repository'


Command failed: opam --cli=2.1 list --readonly --external '--resolve=merlin.3.3.4~4.10preview1,yojson.1.7.0,ocamlfind.1.9.6,easy-format.1.3.2,dune.2.7.1,cppo.1.6.9,biniou.1.2.1' returned 20