erlang 关于表达式的不同用法。

看下边的例子，对于不同的表达式，可以用不同的方法去实现，代码可以体会到里边有的不同。%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%filter2( Line )->   Num = re:run(Line, "[0-9]{6}", [{capture,first,list}]),   if      Num /= nomatch ->         {A,[B]} = Num,         F = string:substr(B,1,1),         if            F =:= "0"; F =:= "3"; F =:= "6"->               B;         true->            false         end;      true->         false   end.%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%getvalue(Key,B) when Key =:= "0"; Key =:= "6"; Key =:= "3"->   B;getvalue(_,_)->   false.filter3( Line )->   case re:run(Line, "[0-9]{6}", [{capture,first,list}]) of      nomatch->         false;      Value ->         {A,[B]} = Value,         getvalue( string:left( B, 1 ), B )   end.%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%getvalue2(Key,B) when Key =:= "0"; Key =:= "6"; Key =:= "3"->   B;getvalue2(_,_)->   false.guard( A ) when A =:= nomatch->   false;guard( {A, [B] } )->   getvalue2( string:left( B, 1 ), B ).filter4( Line )->   Ret = re:run(Line, "[0-9]{6}", [{capture,first,list}]),   guard( Ret ).%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%state(X) when X =:= false->      false;state(_) ->      true.test8()->   Array = ["fafds","ac002345ae","afsaf600123", "abcef300425"],   Ssa = [ filter2(Item) || Item <- Array, filter2(Item) /= false ],   Ssb = [ filter3(Item) || Item <- Array, filter3(Item) /= false ],   Ssc = [ filter4(Item) || Item <- Array, filter4(Item) /= false ],   Fun = fun(X)->   if      X =:= false->         false;      true->         true   end         end,   Ls2 = lists:filter( Fun, Ssa ),   Ls = lists:filter( state, Ssa ),   A = 1.