Callback(3) OCaml library Callback(3)

# [NAME](#NAME)

Callback - Registering OCaml values with the C runtime.

# [Module](#Module)

Module Callback

# [Documentation](#Documentation)

Module **Callback**  
: **sig end**

Registering OCaml values with the C runtime.

This module allows OCaml values to be registered with the C runtime under a symbolic name, so that C code can later call back registered OCaml functions, or raise registered OCaml exceptions.

*val register* : **string -> 'a -> unit**

**Callback.register n v** registers the value **v** under the name **n** . C code can later retrieve a handle to **v** by calling [**caml\_named\_value(n)**](/man/os/ocaml/caml_named_value.n) .

*val register\_exception* : **string -> exn -> unit**

**Callback.register\_exception n exn** registers the exception contained in the exception value **exn** under the name **n** . C code can later retrieve a handle to the exception by calling [**caml\_named\_value(n)**](/man/os/ocaml/caml_named_value.n) . The exception value thus obtained is suitable for passing as first argument to **raise\_constant** or **raise\_with\_arg** .

2026-10-23 OCamldoc

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Document: Callback(3o) from ocaml 5.5.2-r0 (Chainguard OS)
Source: https://github.com/ocaml/ocaml