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# 更多关于列表的内容

| 操作符可以用于取列表中的首元素:

47> [M1|T1] = [paris, london, rome].
[paris,london,rome]
48> M1.
paris
49> T1.
[london,rome]

50> L1 = [madrid | T1].
51> L1.
[madrid,london,rome]

-module(tut8).

-export([reverse/1]).

reverse(List) ->
reverse(List, []).

reverse([], Reversed_List) ->
Reversed_List.
52> c(tut8).
{ok,tut8}
53> tut8:reverse([1,2,3]).
[3,2,1]

reverse([1|2,3], []) =>
reverse([2,3], [1|[]])

reverse([2|3], [1]) =>
reverse([3], [2|[1])

reverse([3|[]], [2,1]) =>
reverse([], [3|[2,1]])

reverse([], [3,2,1]) =>
[3,2,1]

lists 模块中包括许多操作列表的函数，例如，列表翻转。所以，在自己动手写操作列表的函数之前是可以先检查是否在模块中已经有了（参考 STDLIB 中 lists(3) 手册）。

-module(tut7).
-export([format_temps/1]).

format_temps(List_of_cities) ->
convert_list_to_c(List_of_cities).

convert_list_to_c([{Name, {f, F}} | Rest]) ->
Converted_City = {Name, {c, (F -32)* 5 / 9}},
[Converted_City | convert_list_to_c(Rest)];

convert_list_to_c([City | Rest]) ->
[City | convert_list_to_c(Rest)];

convert_list_to_c([]) ->

54> c(tut7).
{ok, tut7}.
55> tut7:format_temps([{moscow, {c, -10}}, {cape_town, {f, 70}},
{stockholm, {c, -4}}, {paris, {f, 28}}, {london, {f, 36}}]).
[{moscow,{c,-10}},
{cape_town,{c,21.11111111111111}},
{stockholm,{c,-4}},
{paris,{c,-2.2222222222222223}},
{london,{c,2.2222222222222223}}]

format_temps(List_of_cities) ->
convert_list_to_c(List_of_cities).

format_temps/1 调用 convert_list_to_c/1 函数。covert_list_to_c/1 函数移除 List_of_cities 的首元素，并将其转换为摄氏单位表示 （如果需要）。| 操作符用来将被转换后的元素添加到转换后的剩余列表中：

[Converted_City | convert_list_to_c(Rest)];

[City | convert_list_to_c(Rest)];

convert_list_to_c([]) ->
[].

-module(tut7).
-export([format_temps/1]).

format_temps(List_of_cities) ->
Converted_List = convert_list_to_c(List_of_cities),
print_temp(Converted_List).

convert_list_to_c([{Name, {f, F}} | Rest]) ->
Converted_City = {Name, {c, (F -32)* 5 / 9}},
[Converted_City | convert_list_to_c(Rest)];

convert_list_to_c([City | Rest]) ->
[City | convert_list_to_c(Rest)];

convert_list_to_c([]) ->
[].

print_temp([{Name, {c, Temp}} | Rest]) ->
io:format("~-15w ~w c~n", [Name, Temp]),
print_temp(Rest);
print_temp([]) ->
ok.
56> c(tut7).
{ok,tut7}
57> tut7:format_temps([{moscow, {c, -10}}, {cape_town, {f, 70}},
{stockholm, {c, -4}}, {paris, {f, 28}}, {london, {f, 36}}]).
moscow          -10 c
cape_town       21.11111111111111 c
stockholm       -4 c
paris           -2.2222222222222223 c
london          2.2222222222222223 c
ok


-module(tut7).
-export([format_temps/1]).

format_temps(List_of_cities) ->
Converted_List = convert_list_to_c(List_of_cities),
print_temp(Converted_List),
{Max_city, Min_city} = find_max_and_min(Converted_List),
print_max_and_min(Max_city, Min_city).

convert_list_to_c([{Name, {f, Temp}} | Rest]) ->
Converted_City = {Name, {c, (Temp -32)* 5 / 9}},
[Converted_City | convert_list_to_c(Rest)];

convert_list_to_c([City | Rest]) ->
[City | convert_list_to_c(Rest)];

convert_list_to_c([]) ->
[].

print_temp([{Name, {c, Temp}} | Rest]) ->
io:format("~-15w ~w c~n", [Name, Temp]),
print_temp(Rest);
print_temp([]) ->
ok.

find_max_and_min([City | Rest]) ->
find_max_and_min(Rest, City, City).

find_max_and_min([{Name, {c, Temp}} | Rest],
{Max_Name, {c, Max_Temp}},
{Min_Name, {c, Min_Temp}}) ->
if
Temp > Max_Temp ->
Max_City = {Name, {c, Temp}};           % Change
true ->
Max_City = {Max_Name, {c, Max_Temp}} % Unchanged
end,
if
Temp < Min_Temp ->
Min_City = {Name, {c, Temp}};           % Change
true ->
Min_City = {Min_Name, {c, Min_Temp}} % Unchanged
end,
find_max_and_min(Rest, Max_City, Min_City);

find_max_and_min([], Max_City, Min_City) ->
{Max_City, Min_City}.

print_max_and_min({Max_name, {c, Max_temp}}, {Min_name, {c, Min_temp}}) ->
io:format("Max temperature was ~w c in ~w~n", [Max_temp, Max_name]),
io:format("Min temperature was ~w c in ~w~n", [Min_temp, Min_name]).
58> c(tut7).
{ok, tut7}
59> tut7:format_temps([{moscow, {c, -10}}, {cape_town, {f, 70}},
{stockholm, {c, -4}}, {paris, {f, 28}}, {london, {f, 36}}]).
moscow          -10 c
cape_town       21.11111111111111 c
stockholm       -4 c
paris           -2.2222222222222223 c
london          2.2222222222222223 c
Max temperature was 21.11111111111111 c in cape_town
Min temperature was -10 c in moscow
ok