4.3.3. Erlang code skill¶

实例1:

function greet(Gender,Name)
  if Gender == male then
    print("Hello, Mr. %s!", Name)
  else if Gender == female then
    print("Hello, Mrs. %s!", Name)
  else
    print("Hello, %s!", Name)
end

=>

greet(male, Name) ->
  io:format("Hello, Mr. ~s!", [Name]);
greet(female, Name) ->
  io:format("Hello, Mrs. ~s!", [Name]);
greet(_, Name) ->
  io:format("Hello, ~s!", [Name]).

guard:

% if ( X>=16 and X=<104)
right_age(X) when X >= 16, X =< 104 ->
  true;
right_age(_) ->
  false.

% if (X < 16 or X > 104)
wrong_age(X) when X < 16; X > 104 ->
  true;
wrong_age(_) ->
  false.

[orelse]与[;]的区别:

% 打印:a
do1(A) when A/0==1 ; true ->
  io:format("a~n");
do1(_A) ->
  io:format("b~n").

% 打印:b
do1(A) when A/0==1 orelse true ->
  io:format("a~n");
do1(_A) ->
  io:format("b~n").

说明: orelse在前一guard抛错时,继续判断下一guard
而「;」则抛错时，忽略之后的guard

代码技巧:

if State =/= locked ->
  do_lock().
=>
State =/= locked andalso do_lock().