[erlang-questions] reference a fun from its atom name

[Roberto Ostinelli]

Dear list,

is it possible to reference a fun from its atom name? For instance:

1> eunit:test({generator, fun hello_test_/0}).

-> everything is ok.

2> FunName = 'hello_test_/0'.

'hello_test_/0'

3> eunit:test({generator, fun FunName}).

* 1: syntax error before: '}'

Any ideas?

Thank you,

r.

[Michael Uvarov]

Use fun M:F/A, where M is a module name, F is a function name and A is arity.
M and F are atoms, A is non_neg_integer,


17> A = 1.
1
18> X = fun lists:reverse/A.
#Fun<lists.reverse.1>
19> X([1,2,3]).
[3,2,1]
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[Michael Uvarov]

F = hello_test_, Fun = fun ?MODULE:F/0.

[Tilman Holschuh]

Did you try?

fun() -> apply(?MODULE, hello_test_, []) end.

Cheers
- Tilman

[Zabrane Mickael]

fun M:F/A

Sent from my iPhone

_______________________________________________

[Roberto Ostinelli]

Thank you all, I ended up using this one.

r.

[Samuel]

> Thank you all, I ended up using this one.
>

>> F = hello_test_, Fun = fun ?MODULE:F/0.

Note that this is not exactly what you were trying to do. I guess you
were trying to create a fun to call a local (possibly unexported
function). The construction above creates a fun that does a fully
qualified call (thus, the function must be exported).

Your problem was that instead of a fun you defined an atom:

2> FunName = 'hello_test_/0'.
'hello_test_/0'

Anything enclosed in '' is an atom. What you were trying to do is probably

2> FunName = fun hello_test_/0.

That's the valid syntax to define a fun, and is roughly (not exactly)
equivalent to
2> FunName = fun() -> hello_test() end.

However the first construct will fail in the shell, because you are in
the erl_eval module context there:

2> FunName = fun hello_test_/0.
** exception error: undefined function erl_eval:hello_test_/0

But it will work if you use it in a module that defines hello_test_()

Regards
--
Samuel

[Roberto Ostinelli]

On Monday, June 18, 2012, Samuel wrote:

> Thank you all, I ended up using this one.
>
>> F = hello_test_, Fun = fun ?MODULE:F/0.

Note that this is not exactly what you were trying to do. I guess you
were trying to create a fun to call a local (possibly unexported
function).

no, this is exactly what I wanted to do. I have a function name as an atom in a variable, and I needed a Fun reference out of it.

Your problem was that instead of a fun you defined an atom:

2> FunName = 'hello_test_/0'.
'hello_test_/0'

Anything enclosed in '' is an atom. What you were trying to do is probably

2> FunName = fun hello_test_/0.

no, believe it or not but I actually may know the difference between an atom and a function. no matter how incredible this may sound.

:)

...r.