Y-combinator in Erlang

Hakan Millroth <>
Tue Jan 7 21:00:19 CET 2003


Now you see why I used to argue that introducing funs etc into Erlang 
would make life tougher for the average joe :-)

-- Hakan

On Tuesday, January 7, 2003, at 06:41  PM, Vladimir Sekissov wrote:

> Good day,
>
> I've surprisingly found Y-combinator very useful to solve practical
> problem of writing recursive anonymous functions in Erlang.
>
> Code were translated to Erlang from
> http://www.ece.uc.edu/~franco/C511/html/Scheme/ycomb.html.
>
>
> -module(lambda).
>
> -export([y/1, mk_fact/0]).
>
> %% Y-combinator itself
> y(X) ->
>   F = fun (P) -> X(fun (Arg) -> (P(P))(Arg) end) end,
>   F(F).
>
> %% Factorial example
> mk_fact() ->
>   F =
>     fun (FA) ->
> 	fun (N) ->
> 	    if (N == 0) -> 1;
> 	       true -> N * FA(N-1)
> 	    end
> 	end
>     end,
>   y(F).
>
>
> From shell:
>
> 1> F = mk_fact().
> #Fun<lambda.3.115879927>
>
> 2> F(5).
> 120
>
> Best Regards,
> Vladimir Sekissov




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