[Haskell-cafe] beginners question about fromMaybe

[Raynor Vliegendhart]

I just noticed that my suggestion doesn't work. You're testing whether
val is Nothing and in my code snipped val has a different type.

On 6/3/09, Raynor Vliegendhart <shinnonoir at gmail.com> wrote:
> 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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>