不使用fun直接写入的方法是使用以布尔测试结尾的begin ... end块：

[ CertainDisease || {CertainDisease,KnownSymptoms} <- Expertise,
                    begin
                        C = length(PatientSymptoms) - length(PatientSymptoms -- KnownSymptoms),
                        C >= 2 andalso C <= 5
                    end ]

定义筛选函数;这样，每个元素只调用一次，消除了重复计算C：

Filter = fun({CertainDisease, KnownSymptoms}) ->
    C = length(PatientSymptoms) - length(PatientSymptoms--KnownSymptoms),
    C >= 2 andalso C <= 5       
end

在你的列表理解中使用它，就像这样：

[CertainDisease ||
    {CertainDisease,KnownSymptoms} <- Expertise,
    Filter({CertainDisease, KnownSymptoms})      
]

您也可以将指派转换成单一产生器：

{[CertainDisease||
     {CertainDisease,KnownSymptoms} <- Expertise,
     C <- [length(PatientSymptoms)-length(PatientSymptoms--KnownSymptoms)],
     C >= 2,
     C <= 5      
]}.