[Haskell-cafe] beginners question about fromMaybe

[Raynor Vliegendhart]

If you're absolutely certain that the lookup always succeeds, then you
can use pattern matching as follows:


       where
           jr  = joinTuples sc x val
           key = getPartialTuple is x
           Just val = Map.lookup key m



On 6/3/09, 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
>
>
> 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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