no switch is set currently

[lost22git]

• opam install utop

[ERROR] No switch is currently set. Please use 'opam switch'
        to set or install a switch

• opam switch list-available

# Listing available compilers from repositories: default
# Name                 # Version # Synopsis
msys2-mingw64          1         MSYS2 MINGW64 Environment
ocaml-option-spacetime 1
          Set OCaml to be compiled with spacetime activated

Opam don't provide Ocaml compiler for android termux users, but I have one built from source.

• ocaml --version

The OCaml toplevel, version 5.5.0+dev0-2025-04-28

I would like to create a custom switch to specify
my Ocaml compiler, how to do this?

[kit-ty-kate]

ocaml-system is the package that is meant for that case, however the package doesn't currently support dev versions, only stable versions. #28455 should fix that whenever it is merged.

You can use this branch by calling opam repo add tmp git+https://github.com/kit-ty-kate/opam-repository.git#ocaml-system-dev or follow the OCaml compiler's guide: https://github.com/ocaml/ocaml/blob/trunk/HACKING.adoc#testing-with-opam

[lost22git]

Hi @kit-ty-kate, could you provide more details about this.

TBH, i am new to Ocaml and have no idea how OPAM works.

i have an ocaml compiler built from ocaml github souce, and i want to attach it to opam switch in order to make opam install working normally.

Thanks.

[kit-ty-kate]

opam repo add tmp git+https://github.com/kit-ty-kate/opam-repository.git#ocaml-system-dev

should allow you to do the usual switch creation, e.g.: opam switch create default ocaml-system

[lost22git]

@kit-ty-kate

it reports some errors like:

; opam repo add tmp git+https://github.com/kit-ty-kate/opam-repository.git#ocaml-system-dev
[WARNING] No switch is currently set, perhaps you meant
          '--set-default'?
Processing  1/1: [tmp: git]
[tmp] no changes from git+https://github.com/kit-ty-kate/opam-repository.git#ocaml-system-dev
[ERROR] No switch is currently set. Please use 'opam switch'
        to set or install a switch

; opam switch create default ocaml-system
[ERROR] No compiler matching `ocaml-system' found, use `opam
        switch list-available' to see what is available, or
        use `--packages' to select packages explicitly.

[kit-ty-kate]

ah my bad, i forgot the --set-default option:

opam repo add tmp --set-default git+https://github.com/kit-ty-kate/opam-repository.git#ocaml-system-dev
opam switch create default ocaml-system

worked for me locally

[lost22git]

@kit-ty-kate thanks, it seems to work fine.

But it still reports these errors when opam install utop.

Not sure if it's because of an issue with the Android platform.

#=== ERROR while compiling lwt.5.9.1 ========================#
# context     2.6.0~alpha1~dev | linux/arm64 | ocaml-system.5.5.0 | git+https://github.com/kit-ty-kate/opam-repository.git#ocaml-system-dev
# path        ~/.opam/default/.opam-switch/build/lwt.5.9.1
# command     ~/.opam/default/bin/dune build -p lwt -j 3 @install
# exit-code   1
# env-file    ~/.opam/log/lwt-23410-6c4f4d.env
# output-file ~/.opam/log/lwt-23410-6c4f4d.out
### output ###
# ./unix_recv_send_utils.h:48:13: error: conflicting types for 'caml_unix_get_sockaddr'
# [...]
#       |             ^
# /data/data/com.termux/files/usr/lib/ocaml/caml/socketaddr.h:69:22: note: expanded from macro 'get_sockaddr'
#    69 | #define get_sockaddr caml_unix_get_sockaddr
#       |                      ^
# /data/data/com.termux/files/usr/lib/ocaml/caml/socketaddr.h:116:3: note: expanded from macro 'caml_unix_get_sockaddr'
#   116 |   caml_unix_get_sockaddr(                                     \
#       |   ^
# /data/data/com.termux/files/usr/lib/ocaml/caml/socketaddr.h:74:13: note: previous declaration is here
#    74 | extern void caml_unix_get_sockaddr (value vaddr,
#       |             ^
# 4 errors generated.

opam install ocamlformat

[ERROR] Package conflict!
  * No agreement on the version of ocaml:
    - (invariant) → ocaml-system → ocaml >= 5.5.0
    - ocamlformat → ocaml < 4.11
    You can temporarily relax the switch invariant with
      `--update-invariant'
  * Incompatible packages:
    - (invariant) → ocaml-system
    - ocamlformat → ocaml < 4.13 → ocaml-base-compiler (=
      4.02.0 | = 4.02.1 | = 4.02.2 | = 4.02.3 | = 4.03.0 |
      = 4.04.0 | = 4.04.1 | = 4.04.2 | = 4.05.0 | = 4.06.0
      | = 4.06.1 | = 4.07.0 | = 4.07.1 | = 4.08.0 | =
      4.08.1 | = 4.10.0 | = 4.10.1 | = 4.10.2 | = 4.11.0 |
      = 4.11.1 | = 4.11.2 | >= 4.12.0~)
  * Incompatible packages:
    - (invariant) → ocaml-system
    - ocamlformat → ocaml < 4.11 → ocaml-variants
  * Missing dependency:
    - ocamlformat → ocaml < 4.11 → 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 <
      3.09.1~ | ocaml-variants < 3.09.1~
    unmet availability conditions, e.g. 'arch != "arm64" &
      arch != "arm32" & arch != "ppc64"'
    unmet availability conditions, e.g. 'sys-ocaml-version
      = "3.09.0"'
    no matching version
  * Missing dependency:
    - ocamlformat → ocaml < 4.11 → ocaml-variants →
      ocaml-beta
    unmet availability conditions:
      'enable-ocaml-beta-repository'
  * Missing dependency:
    - ocamlformat → ocaml < 4.11 → ocaml-variants →
      system-msvc
    unmet availability conditions: 'os = "win32"'

[kit-ty-kate]

The issue for lwt is to report in https://github.com/ocsigen/lwt/issues and most likely due to a lack of testing/support for the Android platform in either OCaml itself or lwt.
And ocamlformat doesn't currently support OCaml trunk. Feel free to open a request in https://github.com/ocaml-ppx/ocamlformat/issues though