foreach loop with counter

问题:

I would like to add a counter in this loop in order to know the row of each element of the list. Do you have a simple solution ?

lists:foreach(fun(X) .... end,Y),

回答1:

Use lists:foldl or write your own function:

lists:foldl(fun(E,Cnt) -> ..., Cnt+1 end, 0, Y),

回答2:

If you want to roll your own, this appear to work as required:

foreach_index(F, [H|T]) ->
    foreach_index(F, [H|T], 0).

foreach_index(F, [H|T], N) ->
    F(H, N),
    foreach_index(F, T, N + 1);

foreach_index(F, [], N) when is_function(F, 2) -> ok.

The function F will be called with two parameters - the individual entry from the list and its index.