Erlangの andalso は第2引数が boolean() じゃなくても良い ref: http://qiita.com/KOU_CHANG/items/a5c6bc7177976a8d8640

file0.erl

1> true andalso false.
false
2> true andalso ok.
ok
3> false orelse true.
true
4> false orelse ok.
ok

file1.erl

Expr1 orelse Expr2
Expr1 andalso Expr2

file2.erl

4> true or garbage.
** exception error: bad argument
     in operator  or/2
        called as true or garbage

file3.erl

all(Pred, [Hd|Tail]) ->
    Pred(Hd) andalso all(Pred, Tail);
all(_, []) ->
    true.

sample_code.erl

get_value(Key, DefinedList) ->
    case DefinedList =:= undefined orelse proplists:get_value(Key, DefinedList) of
        {Key, Value} -> {ok, Value};
        _            -> {error, not_match} %% NOT_MATCH_PROCESS
    end.

sample_code1.erl

get_value(_Key, undefined) ->
    {error, not_match}; %% NOT_MATCH_PROCESS
get_value(Key, DefiendList) ->
    case proplists:get_value(Key, DefinedList) of
        {Key, Value} -> {ok, Value};
        _            -> {error, not_match} %% NOT_MATCH_PROCESS
    end.