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Rev(erse) a list. erse ends up appending all elements once it gets to the end, while erse_tail will reverse as it goes.
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-module(rev). | |
-export([start/0,erse/1,erse_tail/1]). | |
%% recursion with appending | |
erse([First|Rest]) -> erse(Rest)++[First]; | |
erse([]) -> []. | |
%% tail recursion | |
erse_tail(L) -> erse_tail(L,[]). | |
erse_tail([],New) -> New; | |
erse_tail([H|T],New) -> erse_tail(T,[H|New]). | |
%% test | |
start() -> | |
N = 10000, | |
List = lists:seq(1,N), | |
{Time,_} = timer:tc(rev,erse,[List]), | |
{Time2,_} = timer:tc(rev,erse_tail,[List]), | |
%% using the built-in function | |
{Time3,_} = timer:tc(lists,reverse,[List]), | |
io:format("Appending ~p ms~n",[Time/1000]), | |
io:format("Tail recursion ~p ms~n",[Time2/1000]), | |
io:format("BIF ~p ms~n",[Time3/1000]). |
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