Hi,
I have a set of functions:
f1 :: DBRecord -> Maybe Int
f2 :: Int -> IO Maybe DBRecord
f3 :: DBRecord -> Maybe Int
The odd numbered functions are field accessors, accessing a field that
might hold an identifier for another record. The even numbered functions
are record fetch functions that get records from the database. I want to
compose these so that I can navigate structures of joined records in the
database.
How can I concisely compose these functions without having to write a
cascade of case statements such as:
case f1 rec1 of
Nothing -> return Nothing
Just id1 -> do
rec2 <- f2 id2
return $ case rec2 of
Nothing -> return Nothing
Just rec2' -> case f3 rec2' of
....
I understand that if I was just dealing with Maybe I could use the fact
that Maybe is a monad. I am also not sure if composing the IO and the
Maybe will get me what I want (some of the functions only return Maybe Int).
Cheers
Mark
PS Heard this on the 'West Wing' and thought it was appropriate in a way:
A coach goes up to a player and asks "Are you ignorant or apathetic?".
The player replies "I don't know and I don't care".
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