Haskell: Prelude module

Haskell imports Prelude module by default. Prelude module defines most basic functions. You can use the functions defined in Prelude module, without importing them.

$ ghci
GHCi, version 7.10.3: http://www.haskell.org/ghc/  :? for help
Prelude> 
Prelude> head "abcd"
'a'
Prelude> length "abcd"
4
Prelude> reverse "abcd"
"dcba"

functions like head, length, reverse are available in Prelude module.

How to disable this automatic import?
Use the command ‘ghci –XnoImplicitPrelude’ to disable automatic Prelude import.

$ ghci -XNoImplicitPrelude
GHCi, version 7.10.3: http://www.haskell.org/ghc/  :? for help
> 
> head "abcd"

<interactive>:3:1: Not in scope: ‘head’
> 
> length "abcd"

<interactive>:5:1: Not in scope: ‘length’
> 

Since you disabled automatic Prelude import, you are getting above errors while calling head, length functions.

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