1.Modules and Functions
finishing with a full stop "." and a carriage return.
end this part with a ";" which indicates that there is more of this function to come.
The files which are used to store the module must have the same name as the module but with the extension ".erl".
module_name:function_name(arguments).
===== tut1.erl =====
-module(tut1).
-export([fac/1,mult/2]).
fac(1) ->
1;
fac(N) ->
N * fac(N - 1).
mult(X, Y) ->
X * Y.
编译运行：
1> c(tut1).
{ok,tut1}
2> tut2:mult(3,4).
12
2.atoms
===== tut2.erl =====
-module(tut2).
-export([convert/2]).
convert(M, inch) ->
M / 2.54;
convert(N, centimeter) ->
N * 2.54.
编译运行：
9> c(tut2).
{ok,tut2}
10> tut2:convert(3, inch).
1.18110
11> tut2:convert(7, centimeter).
17.7800
12> tut2:convert(3, miles).
** exception error: no function clause matching tut2:convert(3,miles)
13> v(13)
{'EXIT',{function_clause,[{tut2,convert,[3,miles]},
{erl_eval,do_apply,5},
{shell,exprs,6},
{shell,eval_exprs,6},
{shell,eval_loop,3}]}}
3.atoms
===== tut3.erl =====
-module(tut3).
-export([convert_length/1]).
convert_length({centimeter, X}) ->
{inch, X / 2.54};
convert_length({inch, Y}) ->
{centimeter, Y * 2.54}.
编译运行：
14> c(tut3).
{ok,tut3}
15> tut3:convert_length({inch, 5}).
{centimeter,12.7000}
16> tut3:convert_length(tut3:convert_length({inch, 5})).
{inch,5.00000}
4.lists
17> [First |TheRest] = [1,2,3,4,5].
[1,2,3,4,5]
18> First.
1
19> TheRest.
[2,3,4,5]
20> [E1, E2 | R] = [1,2,3,4,5,6,7].
[1,2,3,4,5,6,7]
21> E1.
1
22> E2.
2
23> R.
[3,4,5,6,7]
24> [A, B | C] = [1, 2].
[1,2]
25> A.
1
26> B.
2
27> C.
[]
===== tut4.erl =====
-module(tut4).
-export([list_length/1]).
list_length([]) ->
0;
list_length([First | Rest]) ->
1 + list_length(Rest).
编译运行：
28> c(tut4).
{ok,tut4}
29> tut4:list_length([1,2,3,4,5,6,7]).
7
Erlang does not have a string date type, instead strings can be represented by lists of ASCII characters. So the list [97,98,99] is equivalent to "abc".
4> [97,98,99].
"abc"
5.writing output to a terminal
31> io:format("hello world~n", []).
hello world
ok
32> io:format("this outputs one Erlang term: ~w~n", [hello]).
this outputs one Erlang term: hello
ok
33> io:format("this outputs two Erlang terms: ~w~w~n", [hello, world]).
this outputs two Erlang terms: helloworld
ok
34> io:format("this outputs two Erlang terms: ~w ~w~n", [hello, world]).
this outputs two Erlang terms: hello world
ok
6.Example
A comment starts with a % character and goes on to the end of the line.
===== tut5.erl =====
%% This module is in file tut5.erl
-module(tut5).
-export([format_temps/1]).
%% Only this function is exported
format_temps([])-> % No output for an empty list
ok;
format_temps([City | Rest]) ->
print_temp(convert_to_celsius(City)),
format_temps(Rest).
convert_to_celsius({Name, {c, Temp}}) -> % No conversion needed
{Name, {c, Temp}};
convert_to_celsius({Name, {f, Temp}}) -> % Do the conversion
{Name, {c, (Temp - 32) * 5 / 9}}.
print_temp({Name, {c, Temp}}) ->
io:format("~-15w ~w c~n", [Name, Temp]).
编译运行：
1> c(tut5).
{ok,tut5}
2> tut5:format_temps([{moscow, {c, -10}}, {cape_town, {f, 70}}, {stockholm, {c, -4}}, {paris, {f, 28}}, {london, {f, 36}}]).
moscow -10 c
cape_town 21.1111 c
stockholm -4 c
paris -2.22222 c
london 2.22222 c
ok
收工，下次练习从2.9节开始继续
