Bad error message caused by let expression with too little indentation

[ii8]

test =
  let n =
    identity (2 + 3)
  in n

will give the error:

-- UNFINISHED DEFINITION --------------------------------------------- Main.gren

I got stuck while parsing the `n` definition:

2|   let n = 
            ^
I was expecting to see an expression next. What is it equal to?

Here is a valid definition (with a type annotation) for reference:

    greet : String -> String
    greet name =
      "Hello " ++ name ++ "!"

which is not helpful because it suggests the same idiom of newline + 2 spaces indent after the equal sign, which happens to be valid in a function definition but not in a let expression where you need 5 or more spaces.