[Haskell-beginners] [Haskell-Beginners] Just

Michael Xavier nemesisdesign at gmail.com
Tue Jun 14 17:16:12 CEST 2011

I'm someone will offer a much more eloquent answer after me but here's my
shot as a fellow beginner:

The type Maybe is defined:

data Maybe a = Just a | Nothing

It means that a value of type Maybe String can manifest in 1 of 2 values:
either Nothing, which typically signifies an error has occurred or a "null"
value that you'd see in other programming languages.

Just "foo" is a value that represent a value that is *not* nothing, such as
a successful result from a computation. You can pattern match to get the
value out of it:

case somethingThatProducesAMaybe of
  Just success -> doStuff success
  Nothing -> error "Oh the humanity!"

I hope that helps.
Michael Xavier
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