[Haskell-cafe] beginners question about fromMaybe

[Luke Palmer]

On Tue, Jun 2, 2009 at 4:59 PM, Nico Rolle <nrolle at web.de> wrote:

> hi there
>
> heres a code snipped, don't care about the parameters.
> the thing is i make a lookup on my map "m" and then branch on that return
> value
>
> probePhase is sc [] m = []
> probePhase is sc (x:xs) m
>    | val == Nothing  = probePhase is sc xs m
>    | otherwise       = jr ++ probePhase is sc xs m
>        where
>            jr  = joinTuples sc x (fromMaybe [] val)
>            key = getPartialTuple is x
>            val = Map.lookup key m


Here's my take.   This ought to be equivalent, but I haven't tested.

probePhase is sc m = concatMap prefix
    where
    prefix x = let key = getPartialTuple is x in
               maybe [] (joinTuples sc x) $ Map.lookup key m


>
>
> the line "jr  = joinTuples sc x (fromMaybe [] val)" is kind of ugly
> because i know that it is not Nothing.
> is there a better way to solve this?
> regards
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