[Haskell-beginners] let in GHCI

[Henry Lockyer]

Hello Haskellers

Why is it that in GHCI I can do, for example,

> replicate 6 5
[5,5,5,5,5,5]
> let my6 = replicate 6
> my6 5
[5,5,5,5,5,5]

but if I do 

> sort "bav"
"abv"

this is ok, but 

> let mySort = sort
> mySort "bav"

<interactive>:1:8:
    Couldn't match expected type `()' with actual type `Char'
    Expected type: [()]
      Actual type: [Char]
    In the first argument of `mySort', namely `"bav"'
    In the expression: mySort "bav"

and/or

> mySort [6,5,9]

<interactive>:1:13:
    No instance for (Num ())
      arising from the literal `9'
    Possible fix: add an instance declaration for (Num ())
    In the expression: 9
    In the first argument of `mySort', namely `[6, 5, 9]'
    In the expression: mySort [6, 5, 9]

This is eluding me at the moment..!  ;-)

/ Henry