Haskell Yesod 和 writeFile

Question

I am trying to learn Yesod and trying to implement a simple REST app where everytime a I get a GET request I write something to a file. Right now I have the following handler function:

getTestR =
  do
    return $ writeFile "test.txt" "Just something"
    return $ object ["result" .= "Ok"]

What I was expecting is that the file test.txt would be created and I would obtain a JSON with {result=Ok} . However, I am obtaining the JSON, but the file is not being created.

I guess the writeFile is not being evaluated because of the lazy evaluation, but I have no idea how to overcome this problem. Thanks in advance.

Answer 1

just use liftIO :

getTestR =
  do
    liftIO $ writeFile "test.txt" "Just something"
    return $ object ["result" .= "Ok"]