$ opam install dum
The following actions will be performed:
  ∗ install easy-format 1.3.4 [required by dum]
  ∗ install dum         1.0.3
===== ∗ 2 =====
Do you want to continue? [Y/n] Y

<><> Processing actions <><><><><><><><><><><><><><><><><><><><><><><><><><>  🐫
⬇ retrieved dum.1.0.3  (https://opam.ocaml.org/cache)
⬇ retrieved easy-format.1.3.4  (https://opam.ocaml.org/cache)
∗ installed easy-format.1.3.4
[ERROR] The compilation of dum.1.0.3 failed at "dune build -p dum -j 7 @install".

#=== ERROR while compiling dum.1.0.3 ==========================================#
# context     2.1.4 | macos/x86_64 | ocaml.5.0.0 | https://opam.ocaml.org#750de479
# path        ~/.opam/default/.opam-switch/build/dum.1.0.3
# command     ~/.opam/opam-init/hooks/sandbox.sh build dune build -p dum -j 7 @install
# exit-code   1
# env-file    ~/.opam/log/dum-76865-0392b2.env
# output-file ~/.opam/log/dum-76865-0392b2.out
### output ###
# (cd _build/default && /Users/ludo/.opam/default/bin/ocamlopt.opt -w -40 -g -I .dum.objs/byte -I .dum.objs/native -I /Users/ludo/.opam/default/lib/easy-format -intf-suffix .ml -no-alias-deps -o .dum.objs/native/dum.cmx -c -impl dum.ml)
# File "dum.ml", line 236, characters 9-25:
# 236 | 	assert (Lazy.lazy_is_val (Obj.obj r));
#       	        ^^^^^^^^^^^^^^^^
# Error: Unbound value Lazy.lazy_is_val
# (cd _build/default && /Users/ludo/.opam/default/bin/ocamlc.opt -w -40 -g -bin-annot -I .dum.objs/byte -I /Users/ludo/.opam/default/lib/easy-format -intf-suffix .ml -no-alias-deps -o .dum.objs/byte/dum.cmo -c -impl dum.ml)
# File "dum.ml", line 236, characters 9-25:
# 236 | 	assert (Lazy.lazy_is_val (Obj.obj r));
#       	        ^^^^^^^^^^^^^^^^
# Error: Unbound value Lazy.lazy_is_val