<div dir="ltr">The MaybeT transformer is defined as: <br clear="all"><pre class="haskell"><span style="color: rgb(0, 0, 153);">newtype</span> MaybeT m a = MaybeT <span style="color: black;">{</span>runMaybeT <span style="color: rgb(0, 0, 153);">::</span> m <span style="color: black;">(</span><a href="http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#t:Maybe"><span style="color: rgb(102, 0, 0);">Maybe</span></a> a<span style="color: black;">)</span><span style="color: black;">}</span><br>
&nbsp;<br><span style="color: rgb(0, 0, 153);">instance</span> <a href="http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#t:Functor"><span style="color: rgb(51, 0, 51);">Functor</span></a> m =<span style="color: rgb(0, 102, 0);">&gt;</span> <a href="http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#t:Functor"><span style="color: rgb(51, 0, 51);">Functor</span></a> <span style="color: black;">(</span>MaybeT m<span style="color: black;">)</span> <span style="color: rgb(0, 0, 153);">where</span><br>
  <a href="http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:fmap"><span style="color: rgb(0, 102, 0);">fmap</span></a> f x = MaybeT <a href="http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:."><span style="color: rgb(0, 102, 0);">$</span></a> <a href="http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:fmap"><span style="color: rgb(0, 102, 0);">fmap</span></a> <span style="color: black;">(</span><a href="http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:fmap"><span style="color: rgb(0, 102, 0);">fmap</span></a> f<span style="color: black;">)</span> <a href="http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:."><span style="color: rgb(0, 102, 0);">$</span></a> runMaybeT x<br>
<br>....<br></pre><br>Question:&nbsp; What does &quot;runMaybeT x&quot; mean?<br><br><br>Thanks,<br><br>Daryoush<br>
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