[Haskell-beginners] Bool -> a -> Maybe a, or something similar

[Tacit Sawk]

|Hello!

I tried Hoogle, but it didn't seem to have what I was after. I'm looking 
for something like this:

 > maybeWhen :: Bool -> a -> Maybe a
 > maybeWhen cond =
 >   if cond
 >      then Just
 >      else const Nothing

Is there a builtin that has the above sort of behaviour? I suppose it 
can even be generalised:

 > maybeWhen :: (MonadPlus m) => Bool -> a -> m a
 > maybeWhen cond =
 >   if cond
 >      then return
 >      else const mzero

Tacit
|
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