haskell-doc messages obscured by "async" messages

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With current haskell-mode the output of haskell-doc minor mode (as well as other output in the emacs echo area) is obscured by useless (at least to me) "async" messages when interactive-haskell-mode is started. That is: the string "async" is printed to the echo area, thereby overwriting the actualy useful information ie. the output from doc mode...

To reproduce:

1. enable haskell-doc-mode
2. in any haskell file (with active haskell-mode) move the cursor on a known funtion (e.g. tail)
   → you should see the type of the function in the echo area (e.g. tail :: [a] -> [a])
3. now start interactive-haskell by C-c C-z
4. repeat step from 2.
   → this time the echo area shows "async" instead of the functions type

By bisecting I was able to track down the problem to commit 31426d7
reverting the changes made to haskell-doc.el there (that is: re-inserting the lexical-let) in the current master fixes the problem. I currently don't see why, but maybe someone who understands the special magic taking place there can fix it without reintroducing the use of cl...

[swilde]

#1328 should do the trick, at least it fixes the issue for me.

[fice-t]

Crap, that was my bad. The issue isn't the lexical binding, but the return value of the function. It's just that I put the ending parenthesis in the wrong line which lead to the function returning the symbol async even when it's not async.

The let bindings in your PR don't do anything (as the whole file is already lexically scoped), but you wrapped the 'async in it which fixed the issue.