How to fix "parse error on input" error in haskell?

Question

Prelude Data.Set> :load hello
[1 of 1] Compiling Main             ( hello.hs, interpreted )

hello.hs:11:11: parse error on input `<-'
Failed, modules loaded: none.
Prelude Data.Set> h <- IO.openFile "testtext" IO.ReadMode
Prelude Data.Set> 

On the same line [h <- IO.openFile "testtext" IO.ReadMode] inside hello.hs throws an error. How to fix it? What am I doing wrong?

[EDIT] Source and output: http://pastebin.com/KvEvggQK

Answer 1

You can use <-inside do-block (which you implicitly in GHCI, but not in Haskell files).

In a Haskell file, you are only allowed to write bindings with =.

What you can do is put the following in a Haskell file:

myHandle = do h <- IO.openFile "testtext" IO.ReadMode
              return h

Although, if you think about it a little, it will be exactly the same as:

myHandle = IO.openFile "testtext" IO.ReadMode

myHandle - IO, <- ( >>=) ghci, .

Haskell , , testtext .

---

¹ , <- , .

Answer 2

Try

[h | h <- IO.openFile "testtext" IO.ReadMode]