[erlang-questions] Can I do the same with a fold easily
Mon Oct 19 04:44:10 CEST 2015
Roelof Wobben had
> filter(List, Filter) ->
> lists:filter(Filter, List).
<name list thanks to HTML mail> asked:
> What is the point of this?
Roelof Wobben replied
> These were my solutions to these exercises
> Add a higher-order function to math_functions.erl
> called filter(F, L) which returns all the elements X in L
> for which F(X) is true.
But you did not do that. And you did two things wrong.
First, you swapped the argument order to L, F instead of
the F, L order that you were asked for.
Second, you re-used someone *else's* filter/2 function
instead of writing your own, as the exercise asked.
In software engineering, such reuse is a good thing; the
whole Erlang/OTP system *exists* to be reused like that.
But for an exercise, you were supposed to write
filter(F, [X|Xs]) ->
of true -> ????
; false -> ????
filter(_, ) ->
or something like that, filling in ???? appropriately.
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