[Haskell-cafe] what monad is this?

[Johannes Waldmann]

Dear Cafe,

I was surprised to see  ghc  accept this code

ghci> do let {x = False}; not x
True

because I initially thought: there's a `do`, so there must be some monad,
but which is it? some implicit Identity monad perhaps?

But the type is indeed plain `Bool`, and the explanation is (I think):
there is a `do` but there is no monad, since the translation according to
( https://www.haskell.org/onlinereport/haskell2010/haskellch3.html#x8-470003.14 )
does never produce `(>>=)`.

So, all is fine, nothing to see here.
Perhaps keep in mind as an edge case, useful to confuse students.
Actually, to motivate them to read the language standard ...

- J.W.