Erlang studies abroad

Long term renewal （ Probably ）, Fit has been written several times Erlang Novices who don't understand the meaning of the first pile of code .

attribute

At every writing Erlang There will be something similar at the beginning of the code -module(). The sentence of , They are module attributes . Write a few commonly used predefined module attributes .

-module(modname).  % This is the module declaration , among modname It must be an atom , This attribute must be the first attribute in the file ,modname It must also be the file name ,modname.erl.

-vsn(version)   % Specified version number ,Version It can be any literal data type , It's no use , Generally used for analysis and description .

-import(Mod,[Name1/Arity1]).   %import The declaration lists which functions need to be imported into the module . Once a function is imported from another module , There is no need to specify the module name when calling it .

-export([Name1/Arity1, Name2/Arity2, ...]). % Export the current function , Functions can only be called outside the module after being exported .

-compile(Options).  % add to Options To the compiler options list

Be careful ：-compile(export_all). This compiler option is often used when debugging programs . It will export all functions in the module , No more explicit use -export Marked .

for instance , It means that entering the number of years and months can automatically determine the number of days in this month ,calendar:is_leap_year() It's a built-in function , For details, please refer to Erlang Chinese Manual .

-module(tut1).
%% The following two lines are equivalent 
-compile(export_all).
-export([month_length/2]).
 
month_length(Years,Month) ->
	Leep = calendar:is_leap_year(Years),
	
	case Month of
	    sep -> 30;
        apr -> 30;
        jun -> 30;
        nov -> 30;
        feb when Leep -> 29;
        feb -> 28;
        jan -> 31;
        mar -> 31;
        may -> 31;
        jul -> 31;
        aug -> 31;
        oct -> 31;
        dec -> 31
    end.