Hi, everybody!
I have a problem with opam on my Raspberry Pi 4, for some reason it cannot find appropriate re2 package, even after opam init 
$ opam install re2
Sorry, no solution found: there seems to be a problem with your request.
No solution found, exiting
Although I do have information on this package. In the output, actually, all the versions after 113.x are stroke through, but I cannot show this in the code block below. I suppose it means that those version aren’t available for the system, but I don’t understand why… Maybe it has some relation to ARM.
$ opam info re2
<><> re2: information on all versions <><><><><><><><><><><><><><><><><><><><><>
name re2
all-versions 109.24.00 109.24.01 109.28.00 109.32.00 109.40.00 109.45.00 109.45.01 109.45.02 109.53.00 109.55.00 109.55.02 109.55.03 109.55.04 111.03.00 111.03.01 111.06.00
111.08.00 112.06.00 112.35.00 113.00.00 113.24.00 113.33.00 113.33.00+4.03 113.33.03 -v0.9.0- -v0.9.1- -v0.10.0- -v0.10.1- -v0.11.0- -v0.12.0- -v0.12.1- -v0.13.0- -v0.14.0-
<><> Version-specific details <><><><><><><><><><><><><><><><><><><><><><><><><>
version 113.33.03
repository default
url.src: "https://ocaml.janestreet.com/ocaml-core/113.33/files/re2-113.33.03.tar.gz"
url.checksum: "md5=6d23b0dcb9e72f197fe22eef65204f44"
homepage: "https://github.com/janestreet/re2"
bug-reports: "https://github.com/janestreet/re2/issues"
dev-repo: "git+https://github.com/janestreet/re2.git"
authors: "Jane Street Group, LLC"
maintainer: "Jane Street developers"
license: "Apache-2.0"
depends: "ocaml" {= "4.02.3"}
"ocamlbuild" {build}
"ocamlfind" {build & >= "1.3.2"}
"bin_prot" {>= "113.33.03" & < "113.34.00"}
"core_kernel" {>= "113.33.03" & < "113.34.00"}
"fieldslib" {>= "113.33.03" & < "113.34.00"}
"js-build-tools" {build & >= "113.33.04" & < "113.34.00"}
"ppx_assert" {>= "113.33.03" & < "113.34.00"}
"ppx_bench" {>= "113.33.03" & < "113.34.00"}
"ppx_driver" {>= "113.33.03" & < "113.34.00"}
"ppx_expect" {>= "113.33.03" & < "113.34.00"}
"ppx_inline_test" {>= "113.33.03" & < "113.34.00"}
"ppx_jane" {>= "113.33.03" & < "113.34.00"}
"sexplib" {>= "113.33.03" & < "113.34.00"}
"typerep" {>= "113.33.03" & < "113.34.00"}
"variantslib" {>= "113.33.03" & < "113.34.00"}
synopsis OCaml bindings for RE2, Google's regular expression library
$ ocamlc -version
4.11.1
Please help 
What version of opam do you have?
Could you try with the latest version? (currently 2.1.2)
bash -c "sh <(curl -fsSL https://raw.githubusercontent.com/ocaml/opam/master/shell/install.sh)"
Same problem, but now at least I see why this happens – no support for ARM 
$ opam --version
2.1.2
$ opam install re2
[ERROR] Package conflict!
* No agreement on the version of ocaml:
- (invariant) → ocaml >= 4.05.0
You can temporarily relax the switch invariant with `--update-invariant'
* No agreement on the version of ocaml:
- (invariant) → ocaml >= 4.05.0
* No agreement on the version of ocaml:
- (invariant) → ocaml >= 4.05.0
- re2 → ocaml < 4.03
* No agreement on the version of ocaml:
- (invariant) → ocaml >= 4.05.0
- re2 → ocaml >= 4.00.0
* No agreement on the version of core:
- re2 → core
- re2 → core = 111.06.00
* No agreement on the version of pa%5founit:
- re2 → pa_ounit
* Missing dependency:
- re2 → ocaml < 4.03 → ocaml-base-compiler < 3.07+1 | ocaml-system < 3.07+1 | ocaml-variants < 3.8~
unmet availability conditions: 'arch != "arm64" & arch != "arm32" & arch != "ppc64"'
unmet availability conditions: 'sys-ocaml-version = "3.07"'
no matching version
* Missing dependency:
- re2 → ocaml < 4.03 → ocaml-base-compiler = 3.07+1 | ocaml-system = 3.07+1 | ocaml-variants < 3.8~
unmet availability conditions: 'arch != "arm64" & arch != "arm32" & arch != "ppc64"'
unmet availability conditions: 'sys-ocaml-version = "3.07+1"'
no matching version
* Missing dependency:
- re2 → ocaml < 4.03 → ocaml-base-compiler = 3.07+2 | ocaml-system = 3.07+2 | ocaml-variants < 3.8~
unmet availability conditions: 'arch != "arm64" & arch != "arm32" & arch != "ppc64"'
unmet availability conditions: 'sys-ocaml-version = "3.07+2"'
no matching version
* Missing dependency:
- re2 → ocaml < 4.03 → ocaml-base-compiler = 3.08.0 | ocaml-system < 3.08.1~ | ocaml-variants < 3.08.1~
unmet availability conditions: 'arch != "arm64" & arch != "arm32" & arch != "ppc64"'
unmet availability conditions, e.g. 'sys-ocaml-version = "3.08.0"'
no matching version
* Missing dependency:
- re2 → ocaml < 4.03 → ocaml-base-compiler = 3.08.1 | ocaml-system < 3.08.2~ | ocaml-variants < 3.08.2~
unmet availability conditions: 'arch != "arm64" & arch != "arm32" & arch != "ppc64"'
unmet availability conditions, e.g. 'sys-ocaml-version = "3.08.1"'
no matching version
* Missing dependency:
- re2 → ocaml < 4.03 → ocaml-base-compiler = 3.08.2 | ocaml-system < 3.08.3~ | ocaml-variants < 3.08.3~
unmet availability conditions: 'arch != "arm64" & arch != "arm32" & arch != "ppc64"'
unmet availability conditions, e.g. 'sys-ocaml-version = "3.08.2"'
no matching version
* Missing dependency:
- re2 → ocaml < 4.03 → ocaml-base-compiler = 3.08.3 | ocaml-system < 3.08.4~ | ocaml-variants < 3.08.4~
unmet availability conditions: 'arch != "arm64" & arch != "arm32" & arch != "ppc64"'
unmet availability conditions, e.g. 'sys-ocaml-version = "3.08.3"'
no matching version
* Missing dependency:
- re2 → ocaml < 4.03 → ocaml-base-compiler = 3.08.4 | ocaml-system < 3.08.5~ | ocaml-variants < 3.08.5~
unmet availability conditions: 'arch != "arm64" & arch != "arm32" & arch != "ppc64"'
unmet availability conditions, e.g. 'sys-ocaml-version = "3.08.4"'
no matching version
* Missing dependency:
- re2 → ocaml < 4.03 → ocaml-base-compiler = 3.09.0 | ocaml-system < 3.09.1~ | ocaml-variants < 3.09.1~
unmet availability conditions: 'arch != "arm64" & arch != "arm32" & arch != "ppc64"'
unmet availability conditions, e.g. 'sys-ocaml-version = "3.09.0"'
no matching version
No solution found, exiting