Hi,
I'm trying to construct a module that have a function taking polymorphic
arguments. I want to use this module as a local module in different
places, where the function implementation is different. The module has
the signature:
module type Foo_sig =
sig
val foo : 'a -> 'a
end
If I have a function definition:
let foo_impl a =
a
I'm allowed to write:
let _ = let module Foo : Foo_sig =
struct
let foo = foo_impl
end
in
()
However I want to have a function that creates the module and take the
"foo_impl" as argument:
let test f =
let module Foo : Foo_sig =
struct
let foo = f
end
in
()
and then later I would like to use it like:
let _ = test foo_impl
However, compiling it fails with:
Error: Signature mismatch:
Modules do not match: sig val foo : '_a end is not included in
Foo_sig
Values do not match:
val foo : '_a
is not included in
val foo : 'a -> 'a
Is there some trick to force f to have ('a -> ')? I have tried with "let
test (f : 'a -> 'a)" but then it complains that f has type ('_a -> '_a).
Any other suggestions/design patterns for solving these situations,
without rewriting the whole structure of the application, would also be
highly appreciated.
Thanks,
Hans
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