Cannot Execute Org-Babel Haskell Block

Question

In an org-mode file:

#+BEGIN_SRC haskell
let x = "test"
putStrLn x
#+END_SRC

yields:

executing Haskell code block...
if: ‘org-babel-script-escape’ expects a string

Answer 1

I've solved it writing the header argument :results output after the declaration of the language in the head of the block source.

#+BEGIN_SRC haskell :results output

Answer 2

I didn't manage to comprehend the source code inducing the error, but...

I have same error with #+BEGIN_SRC haskell.

However, #+BEGIN_SRC haskell :results value :eval (inferior-haskell-start-process) works for some reason.

I have

haskell-mode       20180601.143  installed
org                9.1.13        installed