sandbox/pe/chapter4.erl

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-module(chapter4).
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-export([t2l/1, timeit/1, date_string/0]).
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% 2. The BIF tuple_to_list(T) converts the elements of the tuple T to
% a list. Write a function called my_tuple_to_list(T) that does the
% same thing only not using the BIF that does this.
t2l(T) ->
[ element(I, T) || I <- lists:seq(1, tuple_size(T)) ].
% 3. Look up the definitions of erlang:now/0, erlang:date/0, and
% erlang:time/0. Write a function called my_time_func(F), which
% evaluates the fun F and times how long it takes. Write a function
% called my_date_string() that neatly formats the current date and
% time of day.
% erlang:time -> Returns the current time as {Hour, Minute, Second}.
% erlang:date -> Returns the current date as {Year, Month, Day}.
% erlang:now -> deprecated, should use erlang:timestamp
% erlang:timestamp -> Returns current Erlang system time on the format
% {MegaSecs, Secs, MicroSecs}.
% erlang:system_time(Unit) -> Returns current Erlang system time
% converted into the Unit passed as argument.
timeit(F) ->
Started = erlang:system_time(microsecond),
F(),
{erlang:system_time(microsecond) - Started, microsecond}.
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date_string() ->
{Hour, Minute, Second} = erlang:time(),
{Year, Month, Day} = erlang:date(),
io:format("~w-~2..0w-~2..0w ~2..0w:~2..0w:~2..0w",
[Year, Month, Day, Hour, Minute, Second]).
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% 4. Advanced: Look up the manual pages for the Python datetime
% module. Find out how many of methods in the Python datetime class
% can be implemented using the time-related BIFs in the erlang
% module. Search the erlang manual pages for equivalent
% routines. Implement any glaring omissions.
% 5. Write a module called math_functions.erl, exporting the functions
% even/1 and odd/1. The function even(X) should return true if X is an
% even integer and otherwise false. odd(X) should return true if X is
% an odd integer.
% 6. 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.
% 7. Add a function split(L) to math_functions.erl, which returns
% {Even, Odd} where Even is a list of all the even numbers in L and
% Odd is a list of all the odd numbers in L. Write this function in
% two different ways using accumulators and using the function filter
% you wrote in the previous exercise.