[Haskell-cafe] Haskell Data Structure design

[Guru Devanla]

Hello All,

I am just getting myself to code in Haskell and would like to design
advice.  Below, I have a made up example:




data ClassRoom = ClassRoom { classRoomNo:: Integer, extra_fees::Float,
students: Map StudentId Student}
data Student = Student {name::String, feesOwed::Float}
data StudentId =
Integer



get_fees_owed classroom student_id = extra_fees + feesOwed $ (students
classroom) M.! studentid



Here the `get_fees_owed`  needs information from the container
'classroom'.

Here is my question/problem:


I believe I should model most of my code as expressions, rather than
storing pre-computed values such as `fees_owed`.  But,
defining expressions involve passing the container objects all over. For
example, deep down in a function that deals with just
one `student`, I might need the fees owed information. Without, having a
reference to the container, I cannot call get_fees_owed.

Also, I think it hinders composing of functions that just deal with one
student at a time, but end up with some dependency on
the container.

I have several questions related to this design hurdle, but I will start
with the one above.

Thanks!
Guru
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