Error haskell: not in scope. What does that mean?

Question

I started with Haskell today and all the functions I perform on ghci display this message. I just want to know why this is happening. I know there are a lot of questions about this, but this is a simple case and I need to understand this error in the beginning

function3 :: Int -> [Int]
function3 x = [a | a <- [1..x] mod a x == 0]

"Not in scope" means you are trying to use a name which is not defined in the place in which you are trying to use it. In this case, it happens because you left out a comma after [1..x], and so your definition of a within the list comprehension doesn't work as it should. Change it to [a | a <- [1..x], mod a x == 0] — duplode
– duplode, Commented Feb 8, 2017 at 2:40
It help if you include whole GHCi error message in the question. — wizzup
– wizzup, Commented Feb 8, 2017 at 5:23

wizzup · Accepted Answer · 2017-02-08 05:45:02Z

48

Did error happen when you type the function type in GHCi?

$ ghci
GHCi, version 8.0.1: http://www.haskell.org/ghc/  :? for help
Prelude> function3 :: Int -> [Int]

<interactive>:1:1: error:
    Variable not in scope: function3 :: Int -> [Int]
Prelude>

If it is the case, you have to use multiple line input

Prelude> :{
Prelude| function3 :: Int -> [Int]
Prelude| function3 x = [a | a <- [1..x], mod a x == 0]
Prelude| :}

And noted , before mod

Alternatively, for better workflow, you can save your code to a file and load in GHCi using :load

$ cat tmp/functions.hs 
function3 :: Int -> [Int]
function3 x = [a | a <- [1..x], mod a x == 0]

$ ghci
GHCi, version 8.0.1: http://www.haskell.org/ghc/  :? for help
Prelude> :l tmp/functions.hs 
[1 of 1] Compiling Main             ( tmp/functions.hs, interpreted )
Ok, modules loaded: Main.
*Main> :t function3 
function3 :: Int -> [Int]
*Main>

edited Feb 8, 2017 at 5:45

answered Feb 8, 2017 at 5:33

wizzup

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1 Comment

Malik Koné Over a year ago

In what case would function3 :: Int -> [Int] not throw an error in ghci ?

mLstudent33 · Accepted Answer · 2021-07-15 19:35:26Z

1

For me it was trying to :reload my .hs file in ghci after opening a new session but doing :load full_file_name.hs solved the issue.

answered Jul 15, 2021 at 19:35

mLstudent33

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