[erlang-questions] chained functions

Gianfranco Alongi <>
Tue Jan 24 22:24:31 CET 2012


What an error!
Should be:

If all your functions F_1 ... F_K have the type

 F(Input) ->  {ok,Result} | {error,Reason}

then I would probably write a small sequencer as

seq(X,[]) ->
   X;
seq({ok,Result},[ F | T ]) ->
  seq(F(Res),T);
seq({error,Reason},_) ->
  {error,Reason}.

And call it like

seq({ok,Initial},[ fun F_1, ..., fun F_K ])

/G

(And that's why you don't write your emails in a haste before bed!!!)

On Tue, Jan 24, 2012 at 10:17 PM, Gianfranco Alongi
<> wrote:
> If all your functions F_1 ... F_K have the type
>
> F({ok,Result} | {error,Reason} ) ->  {ok,Result} | {error,Reason}
>
> then I would probably write a small sequencer as
>
> seq({ok,Result},[ F | T ]) ->
>  seq(F(Res),T);
> seq(Error,T) ->
>  Error.
>
> And call it like
>
> seq({ok,Initial},[ fun F_1, ..., fun F_K ])
>
> I always try to tag values, so you can use it to determine flow control.
>
> Cheers
> G
>
> On Tue, Jan 24, 2012 at 8:31 PM, Reynaldo Baquerizo
> <> wrote:
>>
>> A friend of mine asked:
>>
>> ##
>> If you have functions that return {ok, Result} | {error, Reason}
>> how do you chained them? So that you have:
>>
>> w(x(y(z(...))))
>>
>> without building a staircasing. Something that would be done in Haskell
>> with monads.
>> ##
>>
>> I would probably go for:
>>
>> x({ok, Value}) ->
>>  NewValue = <do something with Value>,
>>  {ok, NewValue};
>> x({error, Reason}) ->
>>  {error, Reason}.
>>
>> in each function
>>
>> which brings me other question, when do you tag return values?
>>
>> I tend to only use tagged return values with impure functions, were an
>> error is more likely due to side effects.
>>
>> --
>> Reynaldo
>> _______________________________________________
>> erlang-questions mailing list
>> 
>> http://erlang.org/mailman/listinfo/erlang-questions



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